ALBERT

Description: The swelling property of smectite is dominated by the hydration of exchangeable cations in the interlayer spacing ( interlayer hydration'). By investigating systematically the swelling behavior of various exchangeable cations with different valences and ionic radii, the interlayer hydration of smectite was explored. The swelling behavior of Li+-, K+-, Rb+-, Cs+-, Mg2+-, Sr2+-, Ba2+-, and La3+-montmorillonites in undersaturated conditions was measured precisely over the range 50-150{degrees}C by in situ X-ray diffraction (XRD) analyses. The systematic swelling behavior of ten homocationic montmorillonites, the aforementioned eight homoionic montmorillonites, plus Na+ and Ca2+ from a previous study, and the cation hydration energies were analysed by studying the changes occurring in the basal spacing and the 001 peak width. With decreasing cation hydration energy, swelling curves (i.e. plots of basal spacing vs. relative humidity (RH)) change from continuous (Mg2+, La3+, and Ca2+) to stepwise (Sr2+, Li+, Ba2+, and Na+) to one-layer only (K+, Rb+, and Cs+). For the first two groups, the RH at the midpoint between the one- and two-layer hydration states increased as the cation hydration energy decreased. Under low RH, with increasing temperature, the basal spacings of Mg-, La-, Ca-, Sr-, Li-, and Ba-montmorillonites decreased continuously to the zero-layer hydration state, whereas Na-, K-, Rb-, and Cs-montmorillonites swelled from the zero-layer hydration state even at the lowest temperature (50{degrees}C). A decrease in the basal spacing at the same RH but at different temperatures suggests the existence of metastable states or that the layer-stacking structure changes with temperature. The systematics of the swelling behavior of various homocationic montmorillonites as functions of RH and temperature (

Description: Electron energy-loss spectroscopy (EELS), energy-filtered transmission electron microscopy (EFTEM), and high-resolution transmission electron microscopy (HRTEM) have been applied in mineralogy and materials research to determine the oxidation states of various metals at high spatial resolution. Such information is critical in understanding the kinetics and mechanisms of mineral-microbe interactions. To date, the aforementioned techniques have not been applied widely in the study of such interactions. In the present study, the three techniques above were employed to investigate mineral transformations associated with microbial Fe(III) reduction in magnetite. Shewanella putrefaciens strain CN32, a dissimilatory metal-reducing bacterium, was incubated with magnetite as the sole electron acceptor and lactate as the electron donor for 14 days under anoxic conditions in bicarbonate buffer. The extent of bioreduction was determined by wet chemistry and mineral solids were investigated by HRTEM, EFTEM, and EELS. Magnetite was partially reduced and biogenic siderite formed. The elemental maps of Fe, O, and C and red-green-blue (RGB) composite map for residual magnetite and newly formed siderite were contrasted by the EFTEM technique. The HRTEM revealed nm-sized magnetite crystals coating bacterial cells. The Fe oxidation state in residual magnetite and biogenic siderite was determined using the EELS technique (the integral ratio of L3 to L2). The integral ratio of L3 to L2 for magnetite (6.29) and siderite (2.71) corresponded to 71% of Fe(III) in magnetite, and 24% of Fe(III) in siderite, respectively. A chemical shift (~1.9 eV) in the Fe-L3 edge of magnetite and siderite indicated a difference in the oxidation state of Fe between these two minerals. Furthermore, the EELS images of magnetite (709 eV) and siderite (707 eV) were extracted from the electron energy-loss spectra collected, ranging from 675 to 755 eV, displaying different oxidation states of Fe in the magnetite and siderite phases. The results demonstrate that EELS is a powerful technique for studying the Fe oxidation-state change as a result of microbial interaction with Fe-containing minerals.

Description: Magnetite (Fe3O4) is a key economically valuable component in iron ore and is extracted by dissolution processes, but among the Fe (oxyhydr)oxides its solubility behavior is one of the least understood. The objective of this study was to improve understanding of magnetite dissolution mechanisms leading to thermodynamic equilibrium by comparing the dissolution of two solid samples, one synthetic and one industrial, using oxalic, sulfuric, and nitric acids at varying concentrations and temperatures. Of the three solid-liquid systems investigated, only the system consisting of magnetite and oxalic acid reached an equilibrium state within the duration of an individual experiment (6 h). In this system, increasing the acid concentration resulted in a significant increase in the equilibrium concentration of dissolved Fe. When dissolving synthetic and industrial magnetite, increasing the temperature not only increased the rate of reaction but also affected the concentration of dissolved Fe. Significant effects were observed when increasing the temperature from 15 to 35{degrees}C, but only slight differences were seen on further increases in temperature. Observations regarding the equilibrium state of the sulfuric and nitric acid systems could not be made because equilibrium was not reached. The most important individual observation regarding the equilibrium state of the nitric- and sulfuric-acid systems seems to be that in future studies a much longer reaction time is necessary, due to slow kinetics of the dissolution mechanism. A proton-based mechanism has been hypothesized as the one governing the dissolution of magnetite by these two acids, but only the dissolution of the industrial sample yielded results that were similar for these two acids and consistent with that hypothesis.

Description: Mesoporous materials with pore diameters in the range 2-50 nm forming tubular or fibrous structures are of great interest due to their unique properties. Because they are commonly used as sorbents and catalyst carriers, knowledge of their surface area and porosity is critical. A modified intercalation/ deintercalation method was used to increase the efficiency of nanotube formation from kaolin-group minerals which differ in terms of their degree of structural order. Unlike previous experiments, in the procedure adopted in the present study, methanol was used instead of 1,3-butanediol for grafting reactions and octadecylamine intercalation was also performed. The samples were examined using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and transmission electron microscopy (TEM). The specific surface area and porosity of previously described and newly formed materials were investigated by N2 adsorption/desorption. Compared to results described earlier, the percent yield of nanotubes obtained in the present study was significantly greater only in the case of Maria III' kaolinite, which has high structural order. This increase was obtained mainly by the grafting reaction with methanol. Highly ordered stacking of kaolinite-methanol intercalates was noticed and, thus, the amine intercalation was more efficient. In particular, the use of long-chain octadecylamine significantly increased the nanotube yield. The grafting reaction with methanol procedure yielded fewer nanotubes, however, when applied to poorly ordered samples ( Jaroszow' kaolinite and Dunino' halloysite). In the case of the Maria III' kaolinite, the diameter of the rolled layers observed by TEM was ~30 nm and corresponded to average diameters of newly formed pores (DmN) determined using N2 adsorption/desorption, confirming that nanotubes contributed to an increase in surface area and total pore volume. In the case of Jaroszow' kaolinite and Dunino' halloysite mainly macropores (DmN 〉 100 nm) and mesopores (20 nm 〉 DmN 〉 40 nm) were formed. The pores were attributed to interparticle and interaggregate spaces in the stacks of platy particles and to the small relative number of nanotubes.

Description: Clay processes, mineral reactions, and element budgets in oceans continue to be important topics for scientific investigation, particularly with respect to understanding better the roles of chemistry, formation mechanism, and input from hydrothermal fluids, seawater, and non-hydrothermal mineral phases. To that end, the present study was undertaken. Three samples of submarine metalliferous sediments of hydrothermal origin were studied to investigate the formation of smectite, usually Fe-rich, which takes place in such environments. The samples are from the historical collection returned by the British HMS Challenger expedition (1872-1876) and kept at the Natural History Museum in London. The samples were collected from the vicinity of the Pacific-Antarctic Ridge and the Chile Ridge. The samples were analyzed by means of X-ray diffraction (XRD), chemical analysis, scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX), infrared (IR), and transmission electron microscopy-analytical electron microscopy (TEM-AEM). After removal of biogenic calcite the samples appeared to consist mainly of two low-crystallinity phases mixed intimately: Fe/Mn (oxyhydr)oxides and a Si-Al-Mg-Fe phase of similar chemical characteristics to smectite and with variable proportions of the above elements, as indicated by XRD, IR, and SEM-EDX. In particular, analysis by XRD revealed the presence of highly disordered {delta}-MnO2. The TEM-AEM analysis showed that Fe/MnOOH particles have Fe/Mn ratios in the range 25-0.2 and textures changing from granular to veil-like as the proportion of Mn increased. The smectite-like material has the morphology and chemistry of smectite, as well as 10-15 A lattice fringes. Selected area electron diffraction (SAED) patterns indicated a very poorly crystalline material: in some cases distances between diffraction rings corresponded to d values of smectite. The smectite composition indicated a main Fe-rich dioctahedral component with a substantial Mg-rich trioctahedral component (total octahedral occupancy between 2.02 and 2.51 atoms per O10[OH]2). The (proto-) smectite is interpreted to have formed within the metalliferous sediment, as a slow reaction between Fe/MnOOH, seawater (providing Mg), detrital silicates from the continent (providing Si and Al), and X-ray amorphous silica of hydrothermal origin that adsorbed on Fe/MnOOH phases and deposited with them. This material is possibly in the process of maturation into well crystallized smectite.

Description: Contaminant-transport modeling requires information about the charge of subsurface particle surfaces. Because values are commonly reused many times in a single simulation, small errors can be magnified greatly. Goethite ({alpha}-FeOOH) and pyrolusite ({beta}-MnO2) are ubiquitous mineral phases that are especially contaminant reactive. The objective of the present study was to measure and compare the point of zero charge (PZC) using different methods. The pyrolusite PZC was measured with three methods: mass titration (MT) (PZC = 5.9{+/-}0.1), powder addition (PA) (PZC = 5.98{+/-}0.08), and isoelectric point, IEP (PZC = 4.4{+/-}0.1). The IEP measurement was in agreement with literature values. However, MT and PA resulted in a statistically larger PZC than the IEP measurement. The surface area of pyrolusite, 2.2 m2g-1, was too small to permit PZC determination by the potentiometric titration (PT) method. Goethite PZC values were measured using MT (7.5{+/-}0.1), PT (7.46{+/-}0.09), and PA (7.20{+/-}0.08). The present work presents the first reported instance where MT and PA have been applied to measure the point of zero charge of either pyrolusite or goethite. The results illustrate the importance of using multiple, complementary techniques to measure PZC values accurately.

Description: The use of waste materials from mineral ore processing has much potential for immobilizing pollutants such as arsenic (As) in natural soils and waters. The purpose of the present study was to investigate red mud (RM, a finely textured bauxite-ore residue) as a sequestering agent for arsenate and phosphate, including characterization of the types of surface complexes formed. The mineralogical and structural changes occurring in RM were investigated after exchange with arsenate [As(V)-RM] and phosphate [P(V)-RM] anions at pH 4.0, 7.0, and 10.0. Eight different phases were present in the untreated red mud (RMnt), though 80 wt.% of the crystalline phase consisted of sodalite, hematite, gibbsite, and boehmite. The X-ray diffraction (XRD) data for As(V)-RM revealed an anion-promoted dissolution of the gibbsite, suggesting that this phase was the most active for As(V) sequestration. In addition, the lattice parameters of cancrinite were different in As(V)-RM at pH 7.0 and 10.0 from those in RMnt. The changes may be related to the incorporation of arsenate in the cancrinite cages. X-ray diffraction patterns of P(V)-RM at pH 4.0 and 7.0 revealed the dissolution of sodalite, hematite, and gibbsite, and the formation of a novel phase, berlinite [({alpha},{beta})AlPO4]. The new phases detected through XRD and thermal (TG/DTG) analysis in P(V)-RM probably originated through an initial phosphate-promoted dissolution of some RM phases, followed by a precipitation reaction between the phosphate and Al/Fe ions. The results obtained suggest that phosphate and arsenate, though with different reactivities, were strongly bound to some RM phases, such as gibbsite, cancrinite, sodalite, and hematite through mechanisms such as chemical sorption and coprecipitation reactions. The knowledge acquired will be helpful in selecting alternative materials such as red muds, which currently pose critical economic and environmental challenges related to their disposal, for the decontamination of soils and waters polluted with As.

Description: Toxic dyes must be removed from waste water coming from the textile and paint industries. Adsorption is one possible method of removing dyes under soft' conditions, without the generation of secondary hazardous materials. The present study used the carbonate-containing layered double hydroxides (LDH), Mg-Al and Mg-Zn-Al (with a M2+/M3+ ratio of 3), as adsorbents to remove two industrial colorants, Astrazon Remazol Brilliant Blue and Direct Red, present in low concentrations in aqueous solutions. The physicochemical properties of adsorbents at the surfaces of LDH, as well as the properties of the solutions containing the dyes control how the colorants are removed. Both fresh and calcined LDH were effective in the removal experiments, with effectiveness ranging from 50 to 100%. Analysis of kinetic data demonstrated that the adsorption process fitted the pseudo-second-order model better than the pseudo-first order model, information which is useful for system design in the treatment of wastes from the textile industry. Parameters such as pH of solutions and concentration of dye in solution influenced mainly the initial adsorption rate.

Description: The naturally occurring layered double hydroxides (LDH, or anionic clays) are of particular interest in environmental geochemistry because of their ability to retain hazardous cations and especially anions. However, incorporation of these minerals into predictive models of water-rock interaction in contaminant environments, including radioactive-waste repositories, is hampered by a lack of thermodynamic and stability data. To fill part of this gap the present authors have derived properties of one of the complex multicomponent solid solutions within the LDH family: the hydrotalcite-pyroaurite series, Mg3(Al1-xFex)(OH)8(CO3)0.5{middle dot}2.5H2O. Members of the hydrotalcite-pyroaurite series with fixed MgII/(AlIII+FeIII) = 3 and various FeIII/(FeIII+AlIII) ratios were synthesized by co-precipitation and dissolved in long-term experiments at 23{+/-}2{degrees}C and pH = 11.40{+/-}0.03. The chemical compositions of co-existing solid and aqueous phases were determined by inductively coupled plasma-optical emission spectroscopy, thermogravimetric analysis, and liquid scintillation counting of 55Fe tracers; X-ray diffraction and Raman were used to characterize the solids. Based on good evidence for reversible equilibrium in the experiments, the thermodynamic properties of the solid solution were examined using total-scale Lippmann solubility products, {sum}{Pi}T. No significant difference was observed between values of {sum}{Pi}T from co-precipitation and from dissolution experiments throughout the whole range of Fe/Al ratios. A simple ideal solid-solution model with similar end-member {sum}{Pi}T values (a regular model with 0 〈 WG 〈 2 kJ mol-1) was sufficient to describe the full range of intermediate mineral compositions. In turn, this yielded the first estimate of the standard Gibbs free energy of the pyroaurite end member, Go298,Pyr = -3882.60{+/-}2.00 kJ/mol, consistent with Go298,Htlc = -4339.85 kJ/mol of the hydrotalcite end member, and with the whole range of solubilities of the mixed phases. The molar volumes of the solid-solution at standard conditions were derived from X-ray data. Finally, Helgeson's method was used to extend the estimates of standard molar entropy and heat capacity of the end members over the pressure-temperature range 0-70{degrees}C and 1-100 bar.

Description: Even the most casual observer will recognize that rocks transform to clay minerals over time on Earth, and clay minerals have played a particularly important role in the geologic evolution of our planet as well as the evolution of human civilization. Clay minerals, however, have also played an important role elsewhere in our Solar System, and they provide some of the best evidence of aqueous processes during time periods not accessible in Earth’s rock record. The wealth of new data acquired using a variety of remote sensing techniques on planetary missions, coupled with detailed laboratory studies of meteorites, have increased awareness of this fact over the past several decades. The recent renewed interest in clay minerals formed beyond Earth led to a session on new developments in the study of extraterrestrial clay minerals during the 14th International Clay Conference in Castellaneta Marina, Italy, in 2009, and this issue of Clays and Clay Minerals presents several papers that resulted from that session. The number and variety of minerals have increased during the history of our Solar System, yet clay minerals clearly have existed since at least the time of planetary accretion...

Description: The Al-clay-rich rock units at Mawrth Vallis, Mars, have been identified as mixtures of multiple components based on their spectral reflectance properties and the known spectral character of pure clay minerals. In particular, the spectral characteristics associated with the ~2.2 m feature in Martian reflectance spectra indicate that mixtures of AlOH- and SiOH-bearing minerals are present. The present study investigated the spectral reflectance properties of the following binary mixtures to aid in the interpretation of remotely acquired reflectance spectra of rocks at Mawrth Vallis: kaolinite-opal-A, kaolinite-montmorillonite, montmorillonite-obsidian, montmorillonite-hydrated silica (opal), and glass-illite-smectite (where glass was hydrothermally altered to mixed-layer illite-smectite). The best spectral matches with Martian data from the present study's laboratory experiments are mixtures of montmorillonite and obsidian having ~50% montmorillonite or mixtures of kaolinite and montmorillonite with ~30% kaolinite. For both of these mixtures the maximum inflection point on the long wavelength side of the 2.21 m absorption feature is shifted to longer wavelengths, and in the case of the kaolinite-montmorillonite mixtures the 2.17 m absorption found in kaolinite is of similar relative magnitude to that feature as observed in CRISM (Compact Reconnaissance Imaging Spectrometer for Mars) data. The reflectance spectra of clay mixed with opal and of hydrothermally altered glass-illite-smectite did not represent the Martian spectra observed in this region as well. A spectral comparison of linear vs. intimate mixtures of kaolinite and montmorillonite indicated that for these sieved samples, the intimate mixtures are very similar to the linear mixtures with the exception of the altered glass-illite-smectite samples. However, the 2.17 m kaolinite absorption is stronger in the intimate mixtures than in the equivalent linear mixture. Modified Gaussian Modeling of absorption features observed in reflectance spectra of the kaolinite-montmorillonite mixtures indicated a strong correlation between percent kaolinite in the mixture and the ratio of the area of the 2.16 m band found in kaolinite to the area of the 2.20 m band found in montmorillonite.

Description: The discovery of phyllosilicates in terrains of Noachian age (〉3.5 Ga) on Mars implies a period in the planet's history that was characterized by wetter, warmer conditions that may have been more hospitable for life than the cold and dry conditions prevalent today. More specific information about the original locations and mechanisms of clay mineral formation on Mars is not as well constrained, however, in part because the origin of particular clay minerals is often non-unique. For example, Fe and Mg smectite-bearing deposits on Mars may have formed in various environments, including the weathering profiles of basic volcanic rocks, impact-induced hydrothermal sites, or in bodies of standing water. The identification of lacustrine deposits on Mars is of great interest due to their potential for the preservation of organic material, but identifying any given suite of sedimentary rocks as such is difficult when limited to mineralogy and morphology derived from orbital data. Here, the processes and conditions leading to clay mineral formation in lakes and evaporative marine basins on Earth are reviewed, with a focus on the spatial and stratigraphic distribution of clays in these settings. The goal is to provide criteria to determine if certain Martian clay deposits are consistent with such an origin, which in turn will aid in the identification of possible ancient habitable environments on Mars.

Description: Outer main-belt asteroids are predominantly of the C-type (carbonaceous), suggesting that they are likely parent bodies of carbonaceous chondrites. Abundant phyllosilicates in some classes of carbonaceous chondrites have chemical compositions, mineral associations, and textures that preserve direct evidence of the processes by which carbonaceous chondrites and their parent asteroids originated and evolved to their present state. Serpentine is the dominant hydroxyl-bearing mineral in the most abundant (CM) group of carbonaceous chondrites. Serpentine may have formed as a direct nebular condensate during cooling of the solar nebula, or by aqueous alteration of anhydrous Mg,Fe-silicate precursors. Such alteration of anhydrous precursors may have occurred in the solar nebula prior to assembly of the meteorites' parent bodies or on the parent bodies. The relative proportions of Fe and Mg in fine-grained CM2 serpentines have been used to compare the degree of aqueous alteration of different CM2 chondrites with one another. The Mg content of serpentine increases with increasing overall degree of aqueous alteration, so CM2 chondrites with Mg-rich serpentines experienced a more advanced degree of aqueous alteration than CM2 chondrites with Fe-rich serpentines. Attempts to quantify aqueous alteration of CM chondrites by interpreting electron microprobe analyses in terms of charge-balance and site-occupancy constraints from serpentine stoichiometry have met with mixed success. Despite its imperfections, one widely used alteration index based on serpentine stoichiometry is strongly correlated with the elapsed time since the fall and recovery of witnessed CM chondrite falls. Additionally, volatile organic contaminants introduced during sample processing in the laboratory are associated with serpentine and other matrix phyllosilicates. Together, these post-recovery changes in scientifically important sample attributes imply that oxidation-reduction and other types of weathering and contamination affect these meteorites even during curatorial storage and laboratory processing. The same phyllosilicates that make their carbonaceous-chondritic host rocks scientifically important research targets also render those same rocks extraordinarily vulnerable to terrestrial contamination of some of their most scientifically important attributes. This has possible implications for reconstructing pre-terrestrial (parent body) aqueous alteration phenomena from carbonaceous chondritic meteorites and eventually from samples returned by future missions to asteroids with spectral reflectance properties similar to carbonaceous chondrites.

Description: Using first-principles molecular-dynamics simulations, probable inner-sphere complexes of Fe2+ adsorbed on the edge surfaces of clay minerals were investigated. Ferrous ions are important reductants in natural processes and their properties can be altered significantly by complexation on edge surfaces of clay minerals. However, the microscopic picture of adsorption sites and structures of Fe2+ is difficult to reveal with modern experimental techniques and, therefore, remains unclear. From the results of first-principles molecular-dynamics simulations, evidence has been provided that complexes on ≡Si–O sites were the most stable forms, which should be responsible for the experimentally observed pH-dependent uptake. Such complexation was found to be strong enough to distort the local coordination structures of Si-O tetrahedra in the substrate. Analyses showed that Fe2+–Owater coordination structures were dominated by the solvent with surface groups participating in the complexes via H bonding. The present study provided a microscopic basis for understanding the chemical processes involving surface-complexed Fe2+ ions.

Description: The increasing exploration and exploitation of hydrocarbon resources hosted by oil and gas shales demands the correct measurement of certain properties of sedimentary rocks rich in organic matter (OM). Two essential properties of OM-rich shales, the total specific surface area (TSSA) and cation exchange capacity (CEC), are primarily controlled by the rock’s clay mineral content (i.e. the type and quantity). This paper presents the limitations of two commonly used methods of measuring bulk-rock TSSA and CEC, ethylene glycol monoethyl ether (EGME) retention and visible light spectrometry of Co(III)-hexamine, in OM-rich rocks. The limitations were investigated using a suite of OM-rich shales and mudstones that vary in origin, age, clay mineral content, and thermal maturity.Ethylene glycol monoethyl ether reacted strongly with and was retained by natural OM, producing excess TSSA if calculated using commonly applied adsorption coefficients. Although the intensity of the reaction seems to depend on thermal maturity, OM in all the samples analyzed reacted with EGME to an extent that made TSSA values unreliable; therefore, EGME is not recommended for TSSA measurements on samples containing 〉3% OM.Some evidence indicated that drying at ≥200ºC may influence bulk-rock CEC values by altering OM in early mature rocks. In light of this evidence, drying at 110ºC is recommended as a more suitable pre-treatment for CEC measurements in OM-rich shales. When using visible light spectrometry for CEC determination, leachable sample components contributed to the absorbance of the measured wavelength (470 nm), decreasing the calculated bulk rock CEC value. A test of sample-derived excess absorbance with zero-absorbance solutions (i.e. NaCl) and the introduction of corrections to the CEC calculation are recommended.

Description: Using bentonites to adsorb aflatoxin is an effective method of minimizing the toxicity of aflatoxin to animals and humans. Early studies indicated a more than 10-fold difference in aflatoxin adsorption capacity among different bentonites. The determining mineralogical and chemical properties of the clays in aflatoxin adsorption are still poorly understood. The objective of this study was to test the hypothesis that a bentonite’s selectivity and adsorption capacity for aflatoxin is mainly determined by the ‘size matching’ requirement, on a nm scale, between the non-polar interlayer surface domains and the aflatoxin molecules. The non-polar surface domain size of smectites was varied by (1) selecting smectites with different charge densities; and (2) changing the valence and the size of exchange cations to control the amount of water in the hydration shells of the cations. Infrared spectroscopy and X-ray diffraction were also used to characterize the aflatoxin-smectite complexes to investigate if layer-charge density would affect the bonding strength between aflatoxin and the minerals. A large aflatoxin adsorption capacity and high selectivity for aflatoxin were achieved by selecting smectites that had low charge density as represented by their

Description: The conformational behavior of polymers in clay-polymer nanocomposites (CPN) is not fully understood because of the many factors involved. The purpose of the present study was to investigate the conformational behavior of a polymer at the micro- and meso-scales in order to predict the behavior of tunable CPN. The study used a pH-responsive polymer, polyacrylamide, which has time-dependent hydrolysis response properties, to examine micro-scale conformational behavior of the polymer adsorbed on representative clay-mineral surfaces, SiO2 and Al2O3. A nanocomposite and a microcomposite were used to link meso-scale CPN behavior to micro-scale polymer conformation. The conformational behavior was characterized using in situ, real-time spectroscopic ellipsometry. The contracted coil conformation of polyacrylamide was observed at pH = 3, while extended conformation was observed at pH = 11.5 on both SiO2 and Al2O3 surfaces. At pH = 11.5, the polymer conformation changed from expanded coil to extended conformation over time. The polymer conformation changed more rapidly with the Al2O3 surface due to mineral dissolution at pH = 3 and 11.5. Swelling tests were conducted as functions of pH and time to link the micro-scale phenomena to meso-scale CPN behavior. The results indicated that the swelling potential of CPN corresponded to the conformation of adsorbed polyacrylamide, which varied with pH and time. The swelling potential of CPN was maximized at pH = 11.5 and decreased with decreasing pH, corresponding to the observed micro-scale conformational behavior.

Description: The flavonoid naringin is the main source of the undesirable bitter taste in some citrus juices. In commercial debittering processes, the naringin is adsorbed on non-ionic polymeric resins. Organo-clays (OCs), which have been used as sorbents for organic pollutants, could also have affinity for the naringin molecule, and thus potentially could serve as a debittering agent. The objective of the present study was to characterize the sorption capacity of a prepared OC to evaluate its ability to remove naringin from aqueous solutions, investigating the effect of adsorbent dose, initial concentration of naringin, temperature, contact time, and pH. The OC was prepared by the intercalation of cationic surfactant hexadecyltrimethylammonium bromide in a Mexican bentonite. The host clay and the OC were characterized by X-ray diffraction, Fourier-transform infrared, and nitrogen gas adsorption. The OC showed a surface area of 9.3 m2 g−1, 11.35 nm average pore diameter, and a basal spacing, d001, of 2.01 nm. The adsorbent removed naringin at the rate of 60–72% at 25ºC and pH 3. The sorption capacity increased with pH and temperature. Experimental data were well fitted by both Langmuir and Freundlich adsorption models. Most of the sorption took place during the first 10 min and the equilibrium time was reached within 720 min. The rate of sorption was adjusted to pseudo second-order kinetics.

Description: Garnierites represent significant Ni ore minerals in the many Ni-laterite deposits worldwide. The occurrence of a variety of garnierite minerals with variable Ni content poses questions about the conditions of their formation. From an aqueous-solution equilibrium thermodynamic point of view, the present study examines the conditions that favor the precipitation of a particular garnierite phase and the mechanism of Ni-enrichment, and gives an explanation to the temporal and spatial succession of different garnierite minerals in Ni-laterite deposits. The chemical and structural characterization of garnierite minerals from many nickel laterite deposits around the world show that this group of minerals is formed essentially by an intimate intermixing of three Mg-Ni phyllosilicate solid solutions: serpentine-népouite, kerolite-pimelite, and sepiolite-falcondoite, without or with very small amounts of Al in their composition. The present study deals with garnierites which are essentially Al-free. The published experimental dissolution constants for Mg end-members of the above solid solutions and the calculated constants for pure Ni end-members were used to calculate Lippmann diagrams for the three solid solutions, on the assumption that they are ideal. With the help of these diagrams, congruent dissolution of Ni-poor primary minerals, followed by equilibrium precipitation of Ni-rich secondary phyllosilicates, is proposed as an efficient mechanism for Ni supergene enrichment in the laterite profile. The stability fields of the solid solutions were constructed using [log aSiO2(aq), log ((aMg2+ + aNi2+)/(aH+)2)] (predominance) diagrams. These, combined with Lippmann diagrams, give an almost complete chemical characterization of the solution and the precipitating phase(s) in equilibrium. The temporal and spatial succession of hydrous Mg-Ni phyllosilicates encountered in Ni-laterite deposits is explained by the small mobility of silica and the increase in its activity.

Description: Bentonites are candidate materials for encapsulation of radioactive waste. The cation exchange capacity (CEC) has proved to be one of the most sensitive parameters for detecting changes of mineral properties such as swelling capacity and illitization in alteration experiments. Whether measured differences in CEC values of bentonite buffer samples before and after an experiment are (1) actual differences caused by clay structural changes such as illitization or (2) simply data scatter due to the different methods used by international research teams is an open question. The aim of this study was to measure the CEC of clay samples in five different laboratories using the same method and to evaluate the precision of the values measured. The Cu-trien method and four reference materials of the Alternative Buffer Material (ABM) test project in Äspö, Sweden, were chosen for this interlaboratory study. The precision of the Cu-trien method, which uses visible spectroscopy, was very good with a standard deviation of ±0.7–2.1 meq/100 g for CECs that ranged from 11 to 87 meq/100 g. For the same CEC range, analysis of Cu-trien index cations using inductively coupled plasma (mass spectrometry) and atomic absorption spectroscopy were less precise with a standard deviation of ±2.8–3.9 meq/100 g. Based on the measured precision, greater measured differences in Cu-trien CEC and exchangeable cation values of bentonite buffer samples, before and after an experiment, might be actual differences. Great care must be taken when interpreting measured CEC differences, and analytical characterization of any structural changes may be needed. Compared with results from the ‘International Soil-Analytical Exchange’ (iSE) program for soils, most absolute concentrations were much larger for the clays studied; however, for the two parameters exchangeable Ca2+ and CEC the range was similar to the iSE ring test and, most importantly, the precision was comparable. Future studies should discuss the accuracy of CEC and exchangeable cation values and compare them to alternative CEC methods in which care is taken to prevent dissolution of soluble minerals, such as calcite and gypsum.

Description: To acquire a better understanding of the influence exerted by the presence of Cd2+ during the process of transforming ferrihydrite to goethite, the morphological and structural changes of several samples obtained by the addition of Cd2+ to a suspension of nascent goethite were explored, and their chemical reactivity in acid media assessed. The samples (series Gi) were obtained by adding, at different times during the synthesis process, Cd2+ ions to ferrihydrite (Fe5HO8.4H2O) formed in alkaline media. The suspensions were aged for 5 days at 70ºC, and the amorphous materials were extracted using a HCl solution (series GHCl-i). The X-ray diffraction (XRD) patterns showed that a goethite-like phase was formed, and chemical analyses indicated that the Cd content, xCd, increased with the earlier addition of the Cd2+ ions to the Fe oxyhydroxide suspension. Lattice parameters and cell volume, obtained by the Rietveld simulation of XRD data, indicated an enlargement of the cell parameters of goethite in line with the Cd-for-Fe substitution. In order to determine the influence of oxalate ions on the non-extracted solids, a second set of samples was also prepared that was kept in contact with an ammonium oxalate solution for 4 h (series Gox-i). The dissolution behavior of two series of Cd goethites and of a third series, obtained from coprecipitation of Fe3+ and Cd2+ ions in alkaline media, was observed. Kinetics measurements in 4 M HCl showed that the initial dissolution rate of samples Gox-i decreased with aging time, while the opposite effect was observed for series GHCl-i. Dissolution–time curves were well described by the Kabai equation, and activation energies were calculated using the Arrhenius equation. The results indicate that the presence of Cd during the crystallization process of goethite leads to the formation of a Cd goethite with modified morphology, structural parameters, and chemical reactivity.

Description: The combination of zero-valent iron (ZVI) and a clay-type amendment is often observed to have a synergistic effect on the rate of reduction reactions. In the present study, electrochemical techniques were used to determine the mechanism of interaction between the iron (Fe) and smectite clay minerals. Iron electrodes coated with an evaporated smectite suspension (clay-modified iron electrodes, CMIEs) were prepared using five different smectites: SAz-1, SWa-1, STx-1, SWy-1, and SHCa-1. All the smectites were exchanged with Na+ and one sample of SWy-1 was also exchanged with Mg2+. Potentiodynamic polarization scans and cyclic voltammograms were taken using the CMIEs and uncoated but passivated Fe electrodes. These electrochemical experiments, along with measurements of the amount of Fe2+ and Fe3+ sorbed in the smectite coating, suggested that the smectite removed the passive layer of the underlying Fe electrode during the evaporation process. Cyclic voltammograms taken after the CMIEs were biased at the active-passive transition potential for varying amounts of time suggested that the smectite limited growth of a passive layer, preventing passivation. These results are attributed to the Brønsted acidity of the smectite as well as to its ability to sorb Fe cations. Oxides that did form on the surface of the Fe in the presence of the smectite when it was biased anodically were reduced at a different electrochemical potential from those that form on the surface of an uncoated Fe electrode under otherwise similar conditions; this difference suggested that the smectite reacted with the Fe2+ formed from the oxidation of the underlying Fe. No significant correlation could be found between the ability of the smectite to remove the Fe passive film and the smectite type. The results have implications for the mixing of sediments and Fe particles in permeable reactive barriers, underground storage of radioactive waste in steel canisters, and the use of smectite supports in preventing aggregation of nano-sized zero-valent iron.

Description: Bentonites are candidate materials for encapsulation of radioactive waste. The cation exchange capacity (CEC) has proven to be one of the most sensitive parameters for detecting changes in mineral properties in bentonite-alteration experiments. An interlaboratory study of CECs and exchangeable cations for three reference bentonite buffer materials that were used in the Alternative Buffer Material test (ABM) project in Äspö, Sweden, was conducted to create a suitable database. The present study focused on CEC accuracy and compared CEC methods where care was taken to prevent dissolution of soluble minerals such as calcite and gypsum. The overall quality of the CEC and exchangeable cation values measured using non-Cu-trien CEC methods were good, with CECs of 74–91±0.5–3.3 meq/100 g and exchangeable cation values of 22–61±1.2–3.9 meq/100 g Na + , 7–23±0.8–1.5 meq/100 g Mg 2+ , and 19–39±0.8–1.6 meq/100 g Ca 2+ . The precision was comparable to the standard Cu-trien method even for exchangeable Ca 2+ , although the laboratories used different solution/solid ratios and reaction-time parameters for Cu-trien which affect carbonate dissolution. The MX80 and Dep.CAN bentonite exchangeable Ca 2+ values were more accurate than standard-Cu-trien values. Using the optimized methods of this study, MX80 and Dep.CAN exchangeable Ca 2+ values averaged 20.2±1.6 and 38.8±1.4 meq/100 g which amounts to ~70% of the inflated Cu-trien values. A more complex analysis of the CEC data using different methods, anion analyses, and mineralogical analysis is necessary to obtain plausible and accurate CEC values. Even with a more complicated analytical procedure, the CEC and exchangeable cation values were still not accurate enough because of excess anions. Chloride, sulfate, and dolomite might have increased the exchangeable Na + , Mg 2+ , and Ca 2+ values.

Description: The presence, percentage, origins, and rate of formation of clay minerals have been important components in studies involving the geochemical and structural composition of waste-rock piles. The objective of the present study was to investigate the use of tritium as an indicator of the origin of clay minerals within such piles. Tritium values in pore water, interlayer water, and structural hydroxyl sites of clay minerals were examined to evaluate the origins of clay minerals within waste-rock piles located near Questa, New Mexico. Five clay minerals were identified: kaolinite, chlorite, illite, smectite, and mixed-layer illite-smectite, along with the hydrous sulfate minerals gypsum and jarosite. Analysis of waters derived from clay minerals was achieved by thermal reaction of dry-sieved bulk material obtained from the Questa site. In all Questa samples, the low-temperature water derived from pore-water and interlayer sites, as well as the intermediate-temperature water derived from interlayer cation sites occupied by hydronium and structural hydroxyl ions, show tritium values at or near modern levels for precipitation. Pore water and interlayer water ranged from 5.31 to 12.19 tritium units (TU) and interlayer hydronium and structurally derived water ranged from 3.92 to 7.93 TU. Tritium levels for local precipitation ranged from ~4 to 8 TU. One tritium unit (TU) represents one molecule of 3H1HO in 1018 molecules of 1H1HO. The elevated levels of tritium in structural sites can be accounted for by thermal incorporation of significant amounts of hydronium ions in interlayer cation sites for illite and mixed-layer clays, both common at the Questa site. In low-pH environments, such as those found within Questa waste-rock piles (typically pH ~3), the hydronium ion is an abundant species in the rock-pile pore-water system.

Description: Particle–particle interactions in natural clays can be evaluated by their rheological behavior, but the results are often affected by the physicochemical properties of the clays. The behaviors of two fundamentally different types of clays (low-activity and high-activity) differ with respect to salinity and a time factor (duration of shearing at a given shear rate): illite-rich Jonquiere clay (low-activity clay, Canada) and montmorillonite-rich Wyoming bentonite (high-activity clay, USA). The purpose of the present study was to investigate these different behaviors. Most natural clays exhibit shear-thinning and thixotropic behavior with respect to salinity and the volumetric concentration of the solids. Natural clays also exhibit time-dependent non-Newtonian behavior. In terms of index value and shear strength, low-activity and high-activity clays are known to exhibit contrasting responses to salinity. The geotechnical and rheological characteristics as a function of salinity and the shearing time for the given materials are compared here. The clay minerals were compared to estimate the inherent shear strengths, such as remolded shear strength (which is similar to the yield strength). Low-activity clay exhibits thixotropic behavior in a time-dependent manner. High-activity clay is also thixotropic for a short period of shearing, although rare cases of rheopectic behavior have been measured for long periods of shearing at high shear rates. The change from thixotropic to rheopectic behavior by bentonite clay has little effect at low shearing speeds, but appears to have a significant effect at higher speeds.

Description: The island-arc volcanics situated in the eastern part of the Capîlnas-Techereu nappe (South Apuseni Mountains, Romania) were studied to evaluate the temperature, fluid properties, and mineral chemistry during low-temperature metamorphism. Detailed observations of metamorphic mineral assemblages were conducted using powder X-ray diffraction and electron microprobe. The metamorphism involved albitization of plagioclase feldspar and the formation of mafic phyllosilicates, zeolites, and other hydrous Ca-Al-silicate minerals. Mafic phyllosilicates consisted of transitional dioctahedral-trioctahedral smectites, mixed-layer chlorite-smectite (C/S, 6–96% chlorite), and discrete chlorite. The zeolites were analcime, stilbite ± stellerite, heulandite, laumontite, epistilbite, and mordenite. Also present, as secondary minerals filling amygdales and veins, are prehnite, pumpellyite, and secondary amphibole. Two mineral assemblages were identified which provide important information about metamorphic conditions (temperature, reaction progress, and fluid properties): (1) heulandite + analcime + quartz; and (2) laumontite + albite + quartz + prehnite + pumpellyite ± amphibole. The types of and relations between minerals in the first assemblage suggest the occurrence of low-temperature hydrothermal metamorphism in the zeolite facies at ~125ºC, whereas the second assemblage was metamorphosed at 200ºC. The composition and variability of the mineral assemblages in the study area suggest that, due to slow reaction rates, the low-temperature transformations and mineral assemblages were influenced not only by temperature but also by local rock composition, fluid-rock ratio, and fluid chemistry.

Description: Microwave irradiation as a means for heating bentonites during acid activation has been investigated in the past but it has never been optimized for industrial applications. The purpose of this study was to apply a factorial 23 experimental design to a Serbian bentonite in order to determine the influence of microwave heating on the acid-activation process. The effect of acid activation under microwave irradiation on the textural and structural properties of bentonite was studied as a model reaction. A mathematical, second-order response surface model (RSM) was developed with a central composite design that incorporated the relationships among various process parameters (time, acid concentration, and microwave heating power) and the selected process response of specific surface area of the bentonite. The ranges of values for the process parameters chosen were: time, 5–21 min; acid concentration, 2–7 M; and microwave heating power, 63–172 W. The effect of individual variables and their interaction effects on the textural and structural properties of the bentonite were determined. Statistical analysis showed that the duration of microwave irradiation was less significant than the other two factors. The model showed that increasing the time and acid concentration improved the textural properties of bentonites, resulting in increased specific surface area. This model is useful for setting an optimum value of the activation parameters for achieving the maximum specific surface area. An optimum specific surface area of 142 m2g-1 was achieved with an acid concentration of 5.2 M, activation time of 7.4 min, and microwave power of 117 W.

Description: A diapiric intrusion of clays in the Carlentini Formation (Tortonian) was discovered in a quarry at S. Demetrio High (Hyblean Plateau, Sicily, Italy). Seven clay samples were analyzed by different analytical methods, including X-ray powder diffraction (XRD) and Fourier-transform infrared (FTIR) spectroscopy, to determine the composition and mechanism of formation (sedimentary vs. hydrothermal) of these clays. Ferric saponite, carbonates (calcite and traces of ankerite), quartz, pyrite, and zeolites (phillipsite and harmotome) were detected using XRD and FTIR. This mineral assemblage, dominated by Fe-rich saponite, and the abundance of light rare-earth elements (LREE), Eu, fluid-mobile elements (FME 〉 10× primordial mantle: Li, Be, B, As, Sb, Pb, U, Ba, Sr, Cs), and other incompatible elements (Zr = 169 ppm, Nb = 46 ppm, Th = 11 ppm, on average) imply that S. Demetrio clays precipitated from a mixture of hot Si-rich hydrothermal fluids (350–400ºC) and cold seawater. The evidence is in accord with the affinity of clays for hydrothermally modified mafic and ultramafic rocks, forming the Hyblean lower crust, based on multi-element comparisons, and on the occurrence of trace amounts of chrysotile 2Mc1 and sepiolite. The association of long-chain aliphatic-aromatic hydrocarbons (intensity ratios I2927/I2957 〉 0.5) with hydrothermal clays, the lack of fossils, and the similarity of the IR absorption bands with those of organic compounds detected previously in some metasomatized Hyblean gabbroic xenoliths suggest a possible abiogenic origin of hydrocarbons via a Fischer-Tropsch-type reaction. The S. Demetrio clay diapir was emplaced at shallow crustal levels in the Late Miocene as a consequence of the interaction, at a greater depth, of an uprising basalt magma and the products of an early, serpentinite-hosted hydrothermal system.

Description: Bentonite cake is usually formed on the excavated trench surface that is supported by the bentonite slurry during construction of slurry cutoff walls. The lower hydraulic conductivity of bentonite cakes formed during construction of slurry cutoff walls in comparison to backfill materials provides an additional benefit. In the present study, the hydraulic conductivities of bentonite cakes made using three different bentonites were estimated using the modified fluid-loss test under various pressures. Both the hydraulic conductivities of bentonite cakes and cutoff-wall backfill are important in evaluating the in situ hydraulic performance of slurry cutoff-wall construction. Three bentonite slurry concentrations of 4, 6, and 8% were used to fabricate bentonite cakes that represent common field conditions. X-ray diffraction, cation exchange capacity, and swell-index data were collected to characterize the bentonites. Two modified methods for analyzing fluid-loss test results were used to estimate bentonite cake hydraulic conductivities. In addition, the viscosity as a function of time was measured to explain the sealing capacities of the bentonite slurries. The bentonite-cake hydraulic conductivities ranged from 2.15×10-11 m/s to 2.88×10-10 m/s, which were 10 to 500 times lower than the cutoff wall backfill design. Experimental results for 4 and 6% bentonite slurries were relatively similar, but the 8% slurries were noticeably different. Calculated bentonite-cake thickness and stress distribution indicated that the local void ratio and hydraulic conductivity may vary across the cake thickness. The considerably lower bentonite-cake hydraulic conductivities compared to the cutoff wall backfill design show its significance in slurry cutoff-wall construction practices.

Description: Kaolinite is a common gangue mineral in iron ore and sodium silicate has been used widely as a dispersant of silicate gangue minerals including kaolinite in various iron-ore flotation methods over a wide range of pH. Its actual dispersive effect on kaolinite under iron-ore flotation conditions has received very limited attention, however. The presence of hydrolyzable metal cations in process water further complicates sodium silicate-kaolinite interactions. In the present study, the dispersive effect of sodium silicate on kaolinite particles in distilled water as well as in CaCl2 and MgCl2 solutions was investigated systematically through electrophoretic mobility and colloid-stability studies. The studies were based on controlled pH, which eliminated the dispersive effect of sodium silicate induced by increasing pulp pH, in order to simulate the conditions of iron-ore processing. With pH controlled at constant levels, sodium silicate dispersed kaolinite only when positively charged sites were present on kaolinite surfaces and the zeta potential of kaolinite was more negative than ~-30 mV. Over the pH range from 5 to 10.5, a significant dispersive effect of sodium silicate was only observed at pH 7. In process water, when Ca and Mg were present, the strong coagulation of kaolinite particles caused by the hydrolyzable metal cations could not be dispersed effectively with sodium silicate.

Description: The naturally occurring layered double hydroxides (LDH, or anionic clays) are of particular interest in environmental geochemistry because of their ability to retain hazardous cations and especially anions. However, incorporation of these minerals into predictive models of water-rock interaction in contaminant environments, including radioactive-waste repositories, is hampered by a lack of thermodynamic and stability data. To fill part of this gap the present authors have derived properties of one of the complex multicomponent solid solutions within the LDH family: the hydrotalcite-pyroaurite series, Mg3(Al1-xFex)(OH)8(CO3)0.5{middle dot}2.5H2O. Members of the hydrotalcite-pyroaurite series with fixed MgII/(AlIII+FeIII) = 3 and various FeIII/(FeIII+AlIII) ratios were synthesized by co-precipitation and dissolved in long-term experiments at 23{+/-}2{degrees}C and pH = 11.40{+/-}0.03. The chemical compositions of co-existing solid and aqueous phases were determined by inductively coupled plasma-optical emission spectroscopy, thermogravimetric analysis, and liquid scintillation counting of 55Fe tracers; X-ray diffraction and Raman were used to characterize the solids. Based on good evidence for reversible equilibrium in the experiments, the thermodynamic properties of the solid solution were examined using total-scale Lippmann solubility products, {sum}{Pi}T. No significant difference was observed between values of {sum}{Pi}T from co-precipitation and from dissolution experiments throughout the whole range of Fe/Al ratios. A simple ideal solid-solution model with similar end-member {sum}{Pi}T values (a regular model with 0 〈 WG 〈 2 kJ mol-1) was sufficient to describe the full range of intermediate mineral compositions. In turn, this yielded the first estimate of the standard Gibbs free energy of the pyroaurite end member, Go298,Pyr = -3882.60{+/-}2.00 kJ/mol, consistent with Go298,Htlc = -4339.85 kJ/mol of the hydrotalcite end member, and with the whole range of solubilities of the mixed phases. The molar volumes of the solid-solution at standard conditions were derived from X-ray data. Finally, Helgeson's method was used to extend the estimates of standard molar entropy and heat capacity of the end members over the pressure-temperature range 0-70{degrees}C and 1-100 bar.

Description: The Middle-Upper Miocene-Pliocene sediments near Polatli contain commercial sepiolitic clay deposits. The sepiolite-rich Polatli basin sediments were studied to describe the sepiolitic clay deposits of the area and to assess the environments of formation using X-ray diffraction, optical and scanning electron microscopy, and chemical analysis. The Polatli basin is an elongated, rift-related graben trending NE-SW in central Turkey, filled with continental Late Miocene to Early Pliocene sediments. The sediments which comprise claystone, marl and limestone, dolostone, and evaporites are characteristic deposits of low-salinity, playa-lake depositional environments. These sepiolite-rich deposits include sepiolite, dolomite, and calcite, with minor amounts of palygorskite, quartz, moganite, amorphous silica (opal-CT), and feldspar. The sepiolite shows all the characteristic X-ray diffraction reflections of that mineral, whereas amorphous silica containing sepiolite shows some of the characteristic reflections of sepiolite, but with somewhat broader and less intense basal reflections. In the siliceous deposits, the long, fibrous, and filamentous aggregates of the sepiolite were converted to thick, short fibers, low in Mg, and showing transition to amorphous silica. Major and trace elements (e.g. Si, Al, Fe, Mg, Sr, Ba, etc.) were found almost exclusively in Mg-rich smectitic claystone and detrital silicate-rich rocks, whereas Mg, Ca, and some Si were concentrated in the neoformed minerals in the basin. The rare-earth elements (REE) and some of the high-field strength elements (HFSE), large ion lithophile elements (LILE), and transition elements (TRE) patterns were similar for detrital silicate-rich rocks and formed from neoformed mineral lithologies. The REE, TRE, LILE, and some of the HFSE contents of limestone, dolostone, and sepiolitic claystone were similar while those of detrital silicate-rich rocks and Mg-rich smectitic claystones were similar to each other. PAAS-normalized REE and other trace-element patterns were typically subparallel and depleted in neoformed minerals. All sample groups had positive Eu* anomalies, except Mg-rich smectite (0.80). Limestone, dolostone, and amorphous silica compounds showed slightly negative Ce* anomalies, whereas sepiolitic claystones, Mg-rich smectitic claystones, and detrital silicate-rich rocks had a slightly positive Ce* anomaly.

Description: The objectives of this study were to investigate the effects of chemical parameters on the characterization of W-type zeolite crystals and their intergrowths with other types of zeolites. The crystal size and purity of W-type zeolites are affected significantly by the gel composition with respect to the molar ratios of SiO2/Al2O3 (aluminosilicate module, {alpha}), H2O/K2O (alkainity, {beta}), and water content (H2O/SiO2, {gamma}). The effects of these gel parameters on the synthesis and characterization of W-type zeolite were investigated. Crystalline W-type zeolite of high purity was synthesized using a gel with a molar ratio of Al2O3:6.4SiO2:5.6K2O:164.6H2O at T = 165{degrees}C for a period of 72 h. The effect of excess K2O/SiO2 ratio in a mono-cation (K)-SiO2-Al2O3 gel-composition system on the nanoparticle size and purity of the product was also investigated. Experiments were carried out using the following levels of alkalinity: 21.4, 29.4, and 51.9; aluminosilicate module: 5.0, 6.4, and 10.0; water content: 16.5, 25.7, and 32.9; and excess K2O/SiO2 ratio : from 0.65 to 3.33. The results showed that by increasing the aluminosilicate module at high K2O/SiO2 ratio, the crystallinity and crystal size of the zeolite synthesized increased, while at low alkalinity, the crystallinity and crystal size decreased. Decreasing alkalinity at low aluminosilicate module increased the crystallinity and decreased the crystal size, while at high aluminosilicate module, both decreased. Finally, by increasing the water content at all aluminosilicate module and alkalinity values, the crystallinity and crystal size of the W-type zeolite increased. Excess K2O/SiO2 ratio was the key factor that should be adjusted in the range 0.7-1.0 for synthesis of pure crystals of W-type zeolite.

Description: Toxic dyes must be removed from waste water coming from the textile and paint industries. Adsorption is one possible method of removing dyes under soft' conditions, without the generation of secondary hazardous materials. The present study used the carbonate-containing layered double hydroxides (LDH), Mg-Al and Mg-Zn-Al (with a M2+/M3+ ratio of 3), as adsorbents to remove two industrial colorants, Astrazon Remazol Brilliant Blue and Direct Red, present in low concentrations in aqueous solutions. The physicochemical properties of adsorbents at the surfaces of LDH, as well as the properties of the solutions containing the dyes control how the colorants are removed. Both fresh and calcined LDH were effective in the removal experiments, with effectiveness ranging from 50 to 100%. Analysis of kinetic data demonstrated that the adsorption process fitted the pseudo-second-order model better than the pseudo-first order model, information which is useful for system design in the treatment of wastes from the textile industry. Parameters such as pH of solutions and concentration of dye in solution influenced mainly the initial adsorption rate.

Description: The Kutahya kaolinite deposits are the most important source of raw materials for the ceramics industry in Turkey. To date, no detailed mineralogical or geochemical characterizations of these materials have been carried out; the present study aims to fill that gap. The Kutahya kaolinite deposits formed by alteration of dacite and andesite tuffs related to Neogene volcanism which was associated with extensional tectonics. The kaolinite deposits contain silica and Fe- and Ti-bearing phases (pyrite, goethite, and rutile) in vertical and subvertical veins that diminish and then disappear upward. Mineralogical zonation outward from the main kaolinite deposit is as follows: kaolinite {+/-} smectite + illite + opal-CT + feldspar; feldspar + kaolinite + quartz + smectite + illite; quartz + feldspar + volcanic glass. The veins and mineral distributions demonstrate that hydrothermal alteration was the main process in the development of the kaolinite deposits of the area. The very sharp, intense, diagnostic basal reflections at 7.2 and 3.57 A, as well as non-basal reflections, well defined pseudohexagonal to hexagonal crystallinity with regular outlines, ideal differential thermal analysis-thermal gravimetric curves, and ideal, sharp, infrared spectral bands indicate well crystallized kaolinite. Micromorphologically, the development of kaolinite plates at the edges of altered feldspar and devitrified volcanic glass indicates an authigenic origin. Lateral increase in (SiO2+Fe2O3+MgO+Na2O+CaO+K2O)/(Al2O3+TiO2) from the center of the kaolinite deposit outward also indicates hydrothermal zonation. Enrichment of Sr in altered and partially altered rocks relative to fresh volcanic-rock samples demonstrates retention of Sr and depletion of Rb, Ba, Ca, and K during hydrothermal alteration of sanidine and plagioclase within the volcanic units. In addition, depletion of heavy rare earth elements (HREE) relative to light rare earth elements (LREE) in the kaolinized materials may be attributed to the alteration of hornblende. The negative Eu anomaly suggests the alteration of feldspar by hydrothermal fluids. The isotopic data from kaolinite and smectite indicate that hydrothermal-alteration processes developed at 119.1-186.9{degrees}C and 61.8-84.5{degrees}C, respectively. Thus, the kaolinite deposits formed by hydrothermal alteration of volcanic glass, feldspar, and hornblende by a dissolution-precipitation mechanism which operated under acidic conditions within Neogene dacite, andesite, and tuffs.

Description: Toxic metal contamination of waste waters can be mitigated by metal adsorption to clay and zeolitic minerals, but in developing countries such environmental remediation can be cost prohibitive if these minerals are not readily available. Because of its abundance, low cost, and excellent selectivity for several toxic metal ions, clinoptilolite from the Zlatokop deposit in Serbia was investigated for its ability to remove copper ions from aqueous solutions and serve as an effective local resource for this purpose. The sorption capacity of the clinoptilolite at 298 K varied from 8.3 mg Cu g-1 (for C0 = 100 mg Cu dm-3) to 16.8 mg Cu g-1 (for C0 = 400 mg Cu dm-3). The sorption data were best described by the Freundlich isotherm and the sorption kinetics followed the pseudo-second-order model. Intra-particle diffusion of Cu2+ was present but it is not the rate-limiting step. The sorption of Cu2+ on the clinoptilolite occurred spontaneously, the free energy change decreasing with temperature. The sorption was endothermic and was accompanied by an increase in entropy. Dehydration of the Cu-loaded clinoptilolite at 540{degrees}C led to the formation of nanocrystalline Cu(I) oxide particles with an average size of ~2 nm, suggesting possible novel applications for the Cu-loaded clinoptilolite.

Description: Clay-rich deposits of Upper Cretaceous levels in the Taveiro (Reveles and S. Pedro) and Aveiro (Bustos) regions of west-central Portugal are economically and environmentally important, but detailed chemical and mineralogical characterization is lacking. The purpose of this study was to partially fill that gap by correlating the trace-element geochemistry (particularly the rare earth elements, REE) with the mineralogy of both the whole rock and of the

Description: Blum and Eberl (2004) presented a new technique for determining the surface area of clay minerals in sediment samples by measuring the amount of poly-vinylpyrrolidone (PVP) [CAS#9003-39-8] adsorbed by a sample, and explained how the surface-area determination can be used to determine quantitatively the smectite content of the samples. In the previous method for determining surface area by PVP uptake (Blum and Eberl, 2004; also see the erratum relating to that paper published on p. 214 of the present issue), ~50 mg of Na-saturated smectite was dispersed in 5 mL of water, and 1 mL of 10 wt.% PVP-55 (mean MW 55,000) was added. The sample was centrifuged, a portion of the solution decanted, and the PVP concentration in solution determined by mass after drying. The mass of PVP adsorbed on the sample was then computed by difference. This method, while accurate, had several limitations for its practical application which have now been overcome. One of the limitations of the procedure outlined by Blum and Eberl (2004) was...

Description: Contaminant-transport modeling requires information about the charge of subsurface particle surfaces. Because values are commonly reused many times in a single simulation, small errors can be magnified greatly. Goethite ({alpha}-FeOOH) and pyrolusite ({beta}-MnO2) are ubiquitous mineral phases that are especially contaminant reactive. The objective of the present study was to measure and compare the point of zero charge (PZC) using different methods. The pyrolusite PZC was measured with three methods: mass titration (MT) (PZC = 5.9{+/-}0.1), powder addition (PA) (PZC = 5.98{+/-}0.08), and isoelectric point, IEP (PZC = 4.4{+/-}0.1). The IEP measurement was in agreement with literature values. However, MT and PA resulted in a statistically larger PZC than the IEP measurement. The surface area of pyrolusite, 2.2 m2g-1, was too small to permit PZC determination by the potentiometric titration (PT) method. Goethite PZC values were measured using MT (7.5{+/-}0.1), PT (7.46{+/-}0.09), and PA (7.20{+/-}0.08). The present work presents the first reported instance where MT and PA have been applied to measure the point of zero charge of either pyrolusite or goethite. The results illustrate the importance of using multiple, complementary techniques to measure PZC values accurately.

Description: Mesoporous materials with pore diameters in the range 2-50 nm forming tubular or fibrous structures are of great interest due to their unique properties. Because they are commonly used as sorbents and catalyst carriers, knowledge of their surface area and porosity is critical. A modified intercalation/ deintercalation method was used to increase the efficiency of nanotube formation from kaolin-group minerals which differ in terms of their degree of structural order. Unlike previous experiments, in the procedure adopted in the present study, methanol was used instead of 1,3-butanediol for grafting reactions and octadecylamine intercalation was also performed. The samples were examined using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and transmission electron microscopy (TEM). The specific surface area and porosity of previously described and newly formed materials were investigated by N2 adsorption/desorption. Compared to results described earlier, the percent yield of nanotubes obtained in the present study was significantly greater only in the case of Maria III' kaolinite, which has high structural order. This increase was obtained mainly by the grafting reaction with methanol. Highly ordered stacking of kaolinite-methanol intercalates was noticed and, thus, the amine intercalation was more efficient. In particular, the use of long-chain octadecylamine significantly increased the nanotube yield. The grafting reaction with methanol procedure yielded fewer nanotubes, however, when applied to poorly ordered samples ( Jaroszow' kaolinite and Dunino' halloysite). In the case of the Maria III' kaolinite, the diameter of the rolled layers observed by TEM was ~30 nm and corresponded to average diameters of newly formed pores (DmN) determined using N2 adsorption/desorption, confirming that nanotubes contributed to an increase in surface area and total pore volume. In the case of Jaroszow' kaolinite and Dunino' halloysite mainly macropores (DmN 〉 100 nm) and mesopores (20 nm 〉 DmN 〉 40 nm) were formed. The pores were attributed to interparticle and interaggregate spaces in the stacks of platy particles and to the small relative number of nanotubes.

Description: Clay processes, mineral reactions, and element budgets in oceans continue to be important topics for scientific investigation, particularly with respect to understanding better the roles of chemistry, formation mechanism, and input from hydrothermal fluids, seawater, and non-hydrothermal mineral phases. To that end, the present study was undertaken. Three samples of submarine metalliferous sediments of hydrothermal origin were studied to investigate the formation of smectite, usually Fe-rich, which takes place in such environments. The samples are from the historical collection returned by the British HMS Challenger expedition (1872-1876) and kept at the Natural History Museum in London. The samples were collected from the vicinity of the Pacific-Antarctic Ridge and the Chile Ridge. The samples were analyzed by means of X-ray diffraction (XRD), chemical analysis, scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX), infrared (IR), and transmission electron microscopy-analytical electron microscopy (TEM-AEM). After removal of biogenic calcite the samples appeared to consist mainly of two low-crystallinity phases mixed intimately: Fe/Mn (oxyhydr)oxides and a Si-Al-Mg-Fe phase of similar chemical characteristics to smectite and with variable proportions of the above elements, as indicated by XRD, IR, and SEM-EDX. In particular, analysis by XRD revealed the presence of highly disordered {delta}-MnO2. The TEM-AEM analysis showed that Fe/MnOOH particles have Fe/Mn ratios in the range 25-0.2 and textures changing from granular to veil-like as the proportion of Mn increased. The smectite-like material has the morphology and chemistry of smectite, as well as 10-15 A lattice fringes. Selected area electron diffraction (SAED) patterns indicated a very poorly crystalline material: in some cases distances between diffraction rings corresponded to d values of smectite. The smectite composition indicated a main Fe-rich dioctahedral component with a substantial Mg-rich trioctahedral component (total octahedral occupancy between 2.02 and 2.51 atoms per O10[OH]2). The (proto-) smectite is interpreted to have formed within the metalliferous sediment, as a slow reaction between Fe/MnOOH, seawater (providing Mg), detrital silicates from the continent (providing Si and Al), and X-ray amorphous silica of hydrothermal origin that adsorbed on Fe/MnOOH phases and deposited with them. This material is possibly in the process of maturation into well crystallized smectite.

Description: The swelling property of smectite is dominated by the hydration of exchangeable cations in the interlayer spacing ( interlayer hydration'). By investigating systematically the swelling behavior of various exchangeable cations with different valences and ionic radii, the interlayer hydration of smectite was explored. The swelling behavior of Li+-, K+-, Rb+-, Cs+-, Mg2+-, Sr2+-, Ba2+-, and La3+-montmorillonites in undersaturated conditions was measured precisely over the range 50-150{degrees}C by in situ X-ray diffraction (XRD) analyses. The systematic swelling behavior of ten homocationic montmorillonites, the aforementioned eight homoionic montmorillonites, plus Na+ and Ca2+ from a previous study, and the cation hydration energies were analysed by studying the changes occurring in the basal spacing and the 001 peak width. With decreasing cation hydration energy, swelling curves (i.e. plots of basal spacing vs. relative humidity (RH)) change from continuous (Mg2+, La3+, and Ca2+) to stepwise (Sr2+, Li+, Ba2+, and Na+) to one-layer only (K+, Rb+, and Cs+). For the first two groups, the RH at the midpoint between the one- and two-layer hydration states increased as the cation hydration energy decreased. Under low RH, with increasing temperature, the basal spacings of Mg-, La-, Ca-, Sr-, Li-, and Ba-montmorillonites decreased continuously to the zero-layer hydration state, whereas Na-, K-, Rb-, and Cs-montmorillonites swelled from the zero-layer hydration state even at the lowest temperature (50{degrees}C). A decrease in the basal spacing at the same RH but at different temperatures suggests the existence of metastable states or that the layer-stacking structure changes with temperature. The systematics of the swelling behavior of various homocationic montmorillonites as functions of RH and temperature (

Description: The layer charge density (LCD) of montmorillonite represents the permanent negative charge, its most important property. The LCD can be determined by two different methods, the structural formula method (SFM) and the alkylammonium method (AAM). Other methods of determining the LCD are calibrated against one or the other of these. The results of the two methods differ systematically: SFM values are larger than AAM values and the difference increases with increasing layer charge density. In the present study, the critical parameters of both methods were considered quantitatively in order to identify the most likely reason for the systematic difference. One particularly important argument against the validity of the SFM is that typical SFM values correspond to unrealistically large CEC values that have never been reported. In addition, SFM does not consider the variable charge which causes cations to be adsorbed to the outer surface (at pH 〉4). In contrast to minor constituents, which can of course also affect SFM values, the variable charge can explain only part of the systematic difference. The exchange of pure smectite samples with both Cu-trien and alkylammonium revealed the presence of non-exchangeable, non-structural cations (Na, K, Ca). These cations, together with 10% (or more) variable charge, may explain the differences in LCD values. The non-exchangeable, non-structural cations could stem from undetected traces of feldspar or volcanic glass. The present samples indicated that the systematic difference in LCD values between the two methods is related to the amount of non-exchangeable, non-structural cations only, indicating that the two LCD methods probe different features of smectites. Using the SFM on pure smectite provides a value for the total number of charges (permanent with and without fixed (= non-exchangeable, non-structural) cations plus variable charge). The AAM, on the other hand, provides the charge density of the exchangeable cations (without variable charge).

Description: The use of waste materials from mineral ore processing has much potential for immobilizing pollutants such as arsenic (As) in natural soils and waters. The purpose of the present study was to investigate red mud (RM, a finely textured bauxite-ore residue) as a sequestering agent for arsenate and phosphate, including characterization of the types of surface complexes formed. The mineralogical and structural changes occurring in RM were investigated after exchange with arsenate [As(V)-RM] and phosphate [P(V)-RM] anions at pH 4.0, 7.0, and 10.0. Eight different phases were present in the untreated red mud (RMnt), though 80 wt.% of the crystalline phase consisted of sodalite, hematite, gibbsite, and boehmite. The X-ray diffraction (XRD) data for As(V)-RM revealed an anion-promoted dissolution of the gibbsite, suggesting that this phase was the most active for As(V) sequestration. In addition, the lattice parameters of cancrinite were different in As(V)-RM at pH 7.0 and 10.0 from those in RMnt. The changes may be related to the incorporation of arsenate in the cancrinite cages. X-ray diffraction patterns of P(V)-RM at pH 4.0 and 7.0 revealed the dissolution of sodalite, hematite, and gibbsite, and the formation of a novel phase, berlinite [({alpha},{beta})AlPO4]. The new phases detected through XRD and thermal (TG/DTG) analysis in P(V)-RM probably originated through an initial phosphate-promoted dissolution of some RM phases, followed by a precipitation reaction between the phosphate and Al/Fe ions. The results obtained suggest that phosphate and arsenate, though with different reactivities, were strongly bound to some RM phases, such as gibbsite, cancrinite, sodalite, and hematite through mechanisms such as chemical sorption and coprecipitation reactions. The knowledge acquired will be helpful in selecting alternative materials such as red muds, which currently pose critical economic and environmental challenges related to their disposal, for the decontamination of soils and waters polluted with As.

Description: Magnetite (Fe3O4) is a key economically valuable component in iron ore and is extracted by dissolution processes, but among the Fe (oxyhydr)oxides its solubility behavior is one of the least understood. The objective of this study was to improve understanding of magnetite dissolution mechanisms leading to thermodynamic equilibrium by comparing the dissolution of two solid samples, one synthetic and one industrial, using oxalic, sulfuric, and nitric acids at varying concentrations and temperatures. Of the three solid-liquid systems investigated, only the system consisting of magnetite and oxalic acid reached an equilibrium state within the duration of an individual experiment (6 h). In this system, increasing the acid concentration resulted in a significant increase in the equilibrium concentration of dissolved Fe. When dissolving synthetic and industrial magnetite, increasing the temperature not only increased the rate of reaction but also affected the concentration of dissolved Fe. Significant effects were observed when increasing the temperature from 15 to 35{degrees}C, but only slight differences were seen on further increases in temperature. Observations regarding the equilibrium state of the sulfuric and nitric acid systems could not be made because equilibrium was not reached. The most important individual observation regarding the equilibrium state of the nitric- and sulfuric-acid systems seems to be that in future studies a much longer reaction time is necessary, due to slow kinetics of the dissolution mechanism. A proton-based mechanism has been hypothesized as the one governing the dissolution of magnetite by these two acids, but only the dissolution of the industrial sample yielded results that were similar for these two acids and consistent with that hypothesis.

Description: A number of different types of bentonite deposits formed by hydrothermal alteration and diagenetic processes are to be found in the Ordu area of the Eastern Black Sea region. The Ca- and Na-bentonite deposits are related to Upper Cretaceous tholeitic to calc-alkaline volcanites, predominantly dacite and andesite, and also include rhyodacite with lesser basalt and their pyroclastic equivalents. In the present study, dacite (PR1), perlite (PR2), moderately altered rocks (MPR), and Na- and Ca-bentonites were studied to describe and compare their mineralogical and geochemical properties and their conditions of formation by means of X-ray diffraction, optical microscopy, scanning electron microscopy, and chemical analytical techniques. Ca-bentonites, except for smectite, contain opal-CT, feldspar, biotite, and rarely pyrite, while Na-bentonites contain smectite and less feldspar, opal-CT, kaolinite, and illite. Progressive alteration of the PR2 caused depletion in K2O and Na2O and enrichment in MgO and CaO in all of the Ca-bentonite samples. Na2O was depleted in all of the Na-bentonites and in most of the MPR. The medium and heavy rare earth elements (MREE and HREE) show mass gain or mass loss in the Na-bentonites. The HREE show nearly immobile behavior in the Ca-bentonites. The rare earth elements (REE) and transition elements (TRE) mostly gained mass in the Ca-bentonites in contrast to Na-bentonites. Large-ion lithophile elements (LILE) are strongly depleted in all of the bentonites. The LREE, MREE, and HREE were strongly depleted in most of the MPR samples. TiO2, Lu, Tm, and Tb show immobile behavior in all samples. PR1 exhibits a slightly positive Eu anomaly. Two MPR samples show slightly positive Eu anomalies (1.03, 1.13), and one Na-bentonite sample displays a slightly positive Eu anomaly (1.04). Most of the Na-bentonites have weakly negative Eu anomalies, whereas perlite and the Ca-bentonite have a strongly negative Eu anomaly. The PR1, PR2, MPR, and Na-bentonite present a positive Ce anomaly, and the Ca-bentonite shows a moderately negative Ce anomaly. The Ca-montmorillonites are mainly hydrothermal in origin and derived from alteration of volcanoclastic material in situ and/or in the subaerial environment. The Na-montmorillonites formed by alteration and diagenesis of volcanoclastic material in the sedimentary basin.

Description: Guanidine and imidazole are important functional molecules that constitute the side chain of basic amino acids (arginine and histidine); these molecules are capable of interacting with mineral surfaces. However, little information is available about the effect of these molecules on mineral dissolution, including amorphous silica. In this study, to evaluate the effect of these organic molecules on the dissolution rates of amorphous silica, dissolution experiments were performed in solutions containing these molecules and other related heterocyclic compounds. The dissolution experiments were conducted by the batch method using 0.1 g of amorphous silica and 100 mL of 0.1 mM NaCl solution with 0.0, 0.1, 1.0, and 10.0 mM of guanidine, imidazole, pyrazole, or pyrrole at pH values of 4, 5, and 6. The results demonstrated that these compounds can enhance the dissolution rate of amorphous silica, depending on their ionic speciation in the following order: guanidine = imidazole 〉 pyrazole 〉 pyrrole. When 10.0 mM solutions were used, both guanidine and imidazole greatly increased the dissolution rate with an enhancement factor of 5.5-6.5, pyrazole exhibited a smaller change in the dissolution rate with an enhancement factor of 1.5-2.4, and pyrrole exhibited no significant enhancement. ChemEQL calculations confirmed that guanidine (pK = 13.6) and imidazole (pK = 6.99) are fully protonated and mostly present as cationic species in a pH range of 4-6; therefore, these compounds are capable of interacting with the 〉SiO- sites of amorphous silica. Pyrazole (pK = 2.61) and pyrrole (pK = 0.4), however, existed mostly as neutral forms. The concentrations of cationic species of pyrazole and pyrrole were at least one and three orders of magnitude lower than those of fully protonated compounds, respectively; therefore, pyrazole and pyrrole were less reactive than the fully protonated compounds on the surfaces of amorphous silica.

Description: Studies of the paragenesis of authigenic illite in arkosic sandstones of various regions and ages have revealed that the illitization of kaolinite is an important reaction accounting for the formation of authigenic illite in sandstones during burial diagenesis. The illitization of kaolinite takes place at an intermediate burial depth of 3-4 km, where pressure can reach values of 100 MPa ({approx}1000 bars). The purpose of the present study was to analyze the effect of pressure on the rate of kaolinite illitization in alkaline conditions. Hydrothermal reactions were conducted on KGa-1b kaolinite in KOH solution at 300{degrees}C and under pressures of 500, 1000, and 3000 bars for 1 to 24 h. The visual examination of the X-ray diffraction (XRD) patterns indicated a notable influence of pressure on the reaction rate. Molar percentages of muscovite/illite formed at each time interval were calculated from the analysis of two diagnostic XRD peaks, representing the 060 reflections of kaolinite and muscovite/illite. The data were modeled to obtain the initial rate of conversion at each pressure. The results indicated that the initial rate of kaolinite to muscovite/illite conversion is one order of magnitude greater at 3000 bars than at 500 or 1000 bars. Comparison of these data with those in the literature show a faster conversion rate (several orders of magnitude) in an initially high-alkaline solution than in a near-neutral solution.

Description: The characterization of poorly crystalline minerals formed by weathering is difficult using conventional techniques. The objective of this study was to use cutting-edge spectroscopic techniques to characterize secondary Fe mineralogy in young soils formed in basaltic cinders in a cool, arid environment. The mineralogy of a chronosequence of soils formed on 2, 6, and 15 thousand year old basaltic cinders at Craters of the Moon National Monument (COM) was examined using synchrotron-based X-ray absorption fine structure (XAFS) spectroscopy in combination with selective extractions. Fe K-edge XAFS is useful for determining speciation in poorly crystalline materials such as young weathering products. Over 86% of Fe in the soil clay fractions was contained in poorly crystalline materials, mostly in the form of ferrihydrite, with the remainder in a poorly crystalline Fe-bearing smectite. The XAFS spectra suggest that ferrihydrite in the 15 ka soil clay is more resistant to ammonium oxalate (AOD) extraction than is ferrihydrite in the younger materials. Fe in the poorly crystalline smectite is subject to dissolution during citrate-bicarbonate-dithionite (CBD) extraction. The results indicate that relatively few mineralogical changes occur in these soils within the millennial time frame and under the environmental conditions associated with this study. Although the secondary mineral suite remains similar in the soils of different ages, ferrihydrite crystallinity appears to increase with increasing soil age.

Description: Differentiating clay minerals that formed in a supergene environment during deep chemical weathering from those that formed during hydrothermal alteration at higher temperatures associated with a mineralizing event is important in the exploration for epithermal Au deposits. The purpose of this study was to further elucidate this topic by comparing morphological and chemical properties of clay minerals in saprolite overlying epithermally altered bedrock at the Vera Au deposit, Queensland, Australia, with those of clay minerals in saprolite overlying bedrock adjacent to the epithermal alteration zone. X-ray diffraction (XRD) and analytical transmission electron microscopy (ATEM) investigations identified kaolinite, illite, and interstratified illite-smectite, together with quartz, Fe and Ti oxide minerals, and the sulfate minerals jarosite, gypsum, alunite, and natroalunite. Kaolinite crystals within the weathered argillic alteration zone proximal to the epithermal quartz vein are generally larger (up to 3 {micro}m in diameter) and better formed (subhedral to euhedral) than crystals in saprolite distal to the hydrothermal alteration zone, in which smaller (mostly

Description: The effects of surfactants on bentonites have been of great scientific interest for many years. Even though quaternary alkylammonium salts (QAS) have been studied, very few data are available on the comparative performance of different chain-length QAS for the modification of the surface properties and adsorption properties of bentonites. The objective of this study was to investigate the effect of chain length on the adsorption of cationic surfactants onto bentonite. The surface and adsorption properties of different chain-length QAS, i.e. hexadecyltrimethylammonium bromide (HTAB, C16), tetradecyltrimethylammonium bromide (TTAB, C14), and dodecyltrimethylammonium bromide (DTAB, C12), to produce organo-bentonites (OB) were studied. The concentrations of QAS were selected based on the cation exchange capacity (CEC) of the clay mineral. Zeta potential, swelling, and viscosity measurements and scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier-transform infrared (FTIR) analyses were used to explain the changes in surface properties. The results indicated that the best modification of bentonite was obtained using a 16-carbon chain length QAS (HTAB) in a 1:1 ratio of QAS to CEC. The basal spacing at this concentration was measured to be 22.19 A, which also corresponded to the maximum adsorption density. The OB produced at this concentration showed the best hydrophobic character based on the swelling tests in toluene. The extent of hydrophobicity and adsorption density was correlated with the CEC and alkyl chain of the QAS. All these properties were used to elucidate the mechanism of modification governing the bentonite/QAS system.

Description: The effect of plant species on soil-clay mineralogy has not been studied widely. In the present study, the clay mineralogy of top soils under Sequoia gigantia and grass regimes, maintained side by side for up to 150 y in the parks of several French chateaux, were investigated using X-ray diffraction (XRD) methods and chemical analyses of the clay fractions. The seven paired samples that were studied originated from soils developed on calcareous, granitic, and loess substrates. The XRD data indicated the presence of a trioctahedral chlorite with a trioctahedral hydroxy-Mg sheet in sequoia soils observed in four of seven of the sites whereas it was absent from the adjacent prairie-soil samples. Parent materials influenced the formation of magnesian chlorite as it was observed in all soils developed on granite and in none of the soils developed on limestone. The exchangeability of the interlayer hydroxy-Mg sheet replaced by K+ from newly formed chlorite in a 14 y old sequoia-influenced soil suggests that the mineral was initially a hydroxy-interlayered mineral. Increased stability was observed in the older (100 and 150 y) soil chlorites, indicating a progression of polymerization of the Mg hydroxy-interlayered material. The small amount of chlorite in the whole clay assemblage impeded the observation of changes in Mg content by direct chemical measurements of the clay fractions but the systematically greater amount of exchanged Mg2+ ion measured under sequoia compared with adjacent prairie supports the formation of Mg magnesian chlorite. The results presented indicate, on the one hand, the importance of plant regimes in controlling the soil chemistry and hence the clay mineralogy of surface soil horizons (magnesian chlorites were observed only under sequoia), and, on the other hand, that parent material modulates this plant influence (chlorite formation was observed on granite-derived soils).

Description: NEWMOD(C), developed by R.C. Reynolds, Jr., has been an important tool for evaluating quantitatively X-ray diffraction (XRD) patterns from interstratified clay minerals for more than 20 years. However, a significant drawback to the NEWMOD(C) approach is that analyses are done by forward simulation, making results sensitive to user input and starting-model assumptions. In the present study, a reverse-fitting procedure was implemented in a new program, FITMOD, which automatically minimizes the differences between experimental and simulated XRD patterns. The differences are minimized by varying model parameters (such as Reichweite, crystal-size distribution, cation content, type of disorder, etc.) using the downhill simplex method. The downhill simplex method is a non-linear optimization technique for determining minima of functions. This method does not require calculation of the derivatives of the functions being minimized, an important consideration with many of the parameters in NEWMOD-type simulations. Instead, the downhill simplex method calculates pseudo-derivatives by evaluating sufficient points to define a derivative for each independent variable. The performance of FITMOD was evaluated by fitting a series of synthetic XRD patterns generated by NEWMOD+, yielding agreement factors, Rwp, of

Description: The coefficient of friction of clay minerals at the micro-scale has generally not been studied due to difficulties in obtaining measurements in a bulk-soil volume undergoing shear at such small scales. Information on friction at the micro-scale may provide insight into grain-scale processes that operate in bulk samples or in natural faults. The objective of this study was to develop a method to measure the micro-scale friction coefficient of smectites. The experiments described show that the axial atomic force microscopy method can be adapted to easily obtain accurate coefficient of friction ({micro}) measurements for smectites from force curves involving colloidal probes. The method allows for the measurements to be performed over spatial scales of a few {micro}m, can be carried out under dry conditions or a wide range of aqueous solutions, and requires no calibration beyond making a few microscopic measurements of the probe. This method provides measurements of micro-scale normal and shear forces between minerals, which can be used for a variety of applications such as the study of shear deformation, consolidation, and fault dynamics. Control tests of silica on mica ({micro} = 0.29{+/-}0.02) agree with literature values where limits indicate one standard deviation. Coefficient of friction values for wet and dry Na-montmorillonite were determined to be 0.20{+/-}0.03 and 0.72{+/-}0.03, respectively.

Description: The formation of illite through the smectite-to-illite (S-I) reaction is considered to be one of the most important mineral reactions occurring during diagenesis. In biologically catalyzed systems, however, this transformation has been suggested to be rapid and to bypass the high temperature and long time requirements. To understand the factors that promote the S-I reaction, the present study focused on the effects of pH, temperature, solution chemistry, and aging on the S-I reaction in microbially mediated systems. Fe(III)-reduction experiments were performed in both growth and non-growth media with two types of bacteria: mesophilic (Shewanella putrefaciens CN32) and thermophilic (Thermus scotoductus SA-01). Reductive dissolution of NAu-2 was observed and the formation of illite in treatment with thermophilic SA-01 was indicated by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). A basic pH (8.4) and high temperature (65{degrees}C) were the most favorable conditions for the formation of illite. A long incubation time was also found to enhance the formation of illite. K-nontronite (non-permanent fixation of K) was also detected and differentiated from the discrete illite in the XRD profiles. These results collectively suggested that the formation of illite associated with the biologically catalyzed smectite-to-illite reaction pathway may bypass the prolonged time and high temperature required for the S-I reaction in the absence of microbial activity.

Description: Intercalation of montmorillonites with a mixture of intercalates has not been studied extensively. The objective of the present investigation was to study the effects of phosphonium-based intercalate mixtures on the properties (organic loading and basal spacing) of montmorillonite. These phosphonium-intercalated montmorillonites are promising candidates as high-temperature stable nanofillers for application in clay polymer nanocomposites. Two salts with different cationic heads and chain lengths were mixed in varying molar ratios and the mixtures were intercalated into the interlayer space of montmorillonite. Two sets were chosen based on the chain length and the cationic head-group structure of the two intercalated salts (referred to hereafter as set 1 and set 2). The resultant intercalated montmorillonite was characterized by thermogravimetric analysis, X-ray diffraction, and transmission electron microscopy. The organic loading of the intercalated montmorillonite increased with the proportion of longer carbon-chain intercalate in the mixture. The intensity of the characteristic XRD peak of each intercalate varied with the mole fraction percent of that intercalate in the solution mixture. No marked synergistic effect of the intercalate mixture on the basal spacing and organic loading properties of the intercalated montmorillonite was observed - the proportional influence of individual components was found to be more prominent.

Description: Ruthenium compounds are highly toxic and carcinogenic. In the present study, clinoptilolite was used in the removal of Ru species from aqueous solutions. Clinoptilolite is a good choice of sorbents because it is naturally abundant and therefore cheap. After the process where Ru was removed from the aqueous solution, the clinoptilolite was characterized by X-ray diffraction, X-ray fluorescence, thermogravimetric analysis, and Fourier-transform infrared spectroscopy techniques. The influence of pH, contact time, and temperature on the adsorption of Ru was investigated and the optimum conditions were found to be 2 h of contact time and pH = 2. Pseudo first-order, pseudo second-order, Elovich, and intra-particle diffusion models were used to analyze the adsorption-rate data. The pseudo second-order model was found to be the best kinetics model in terms of matching the experimental results obtained. Adsorption isotherms were constructed to assess the maximum adsorption capacity of clinoptilolite. The Langmuir model fitted the data reasonably well in terms of regression coefficients. Adsorption studies were also performed at different temperatures to calculate the thermodynamic parameters. The numerical value of {Delta}G0 decreased with increasing temperature, indicating that adsorption is favored at higher temperatures. The positive values of {Delta}H0 corresponded to the endothermic nature of the adsorption processes. The proposed method of removal is applicable at an industrial scale.

Description: The industrial assessment of ceramic clays commonly consists of the determination of just two parameters, the particle-size distribution and the chemical composition; other parameters may also be important, however. The aim of the present study was to show that a careful determination of the mineralogical phase content provides valuable additional information on the processing behavior of ceramic clays. Two ceramic clays (W1 and W2) from the Westerwald area, Germany, were evaluated as being the same with respect to industrial screening criteria, but showed different processing properties. In order to elucidate the different behaviors, both clays were investigated comprehensively using a multi-method approach combining physical-chemical and mineralogical methods. Different aggregation characteristics for the two clays were revealed by determining the grain-size distribution with and without Na-pyrophosphate as a dispersant. In addition, W1 showed a greater electrical conductivity and soluble-salt concentration which promoted dispersion behavior. The phase content was identified both for bulk materials and for several grain-size fractions by X-ray diffraction (XRD) and Rietveld analysis. The quantitative phase content was crosschecked with the chemical composition by X-ray fluorescence (XRF) analysis. Additional information was gathered by thermal analysis, cation exchange capacity (CEC) measurements, Mossbauer spectroscopy, and optical microscopy. While bulk samples of W1 and W2 showed nearly the same mineralogical and chemical compositions, investigation of the clay-size fractions (0.6-2 {micro}m,

Description: Hydrothermal syntheses of a silicate structure comprising a single tetrahedral layer, known as ilerite, were conducted in the presence of tin (SnCl4{middle dot}5H2O) as a heteroatom. The main aim of the study was to investigate the influence of the above-mentioned compound on the resulting material, as well as the possibility of isomorphous replacement of Si by Sn atoms. For comparison, unmodified ilerite, ilerite impregnated by SnO2, and ilerite synthesized in the presence of Al (aluminum isopropoxide) were also used. The ilerite structure observed was that of Na-ilerite. Syntheses of samples with various Sn/Si ratios (up to the value of 0.01Sn/4Si) and Al/Si ratios (up to the value of 0.005Al/4Si) resulted in a magadiite structure. Synthesis methods applied to Sn-modified materials were found to be unsuitable for the introduction of tetrahedrally substituted Al. The characterization methods used were X-ray diffraction (XRD), temperature-programmed reduction (TPR), and diffuse reflectance infrared fourier transform (DRIFT) spectroscopy. and these indicated the presence of metal oxide species on the surfaces of the crystals, in addition to a small degree of replacement of Si by Sn or Al in the tetrahedral layers.

Description: Clay minerals are abundant in soils and sediments and often contain Fe. Some varieties, such as nontronites, contain as much as 40 wt.% Fe2O3 within their molecular structure. Several studies have shown that various Fe-reducing micro-organisms can use ferric iron in Fe-bearing clay minerals as their terminal electron acceptor, thereby reducing it to ferrous iron. Laboratory experiments have also demonstrated that chemically or bacterially reduced clays can promote the reductive degradation of various organics, including chlorinated pesticides and nitroaromatics. Therefore, Fe-bearing clays may play a crucial role in the natural attenuation of various redox-sensitive contaminants in soils and sediments. Although the organochlorinated pesticide p,p'-DDT is one of the most abundant and recalcitrant sources of contamination in many parts of the world, the impact of reduced Fe-bearing clays on its degradation has never been documented. The purpose of the present study was to evaluate the extent of degradation of p,p'-DDT during the bacterial reduction of Fe(III) in an Fe-rich clay. Microcosm experiments were conducted under anaerobic conditions using nontronite (sample NAu-2) spiked with p,p'-DDT and the metal-reducing bacteria Shewanella oneidensis MR-1. Similar experiments were conducted using a sand sample to better ascertain the true impact of the clay vs. the bacteria on the degradation of DDT. Samples were analyzed for DDT and degradation products after 0, 3, and 6 weeks of incubation at 30{degrees}C. Results revealed a progressive decrease in p,p'-DDT and increase in p,p'-DDD concentrations in the clay experiments compared to sand and abiotic controls, indicating that Fe-bearing clays may substantially contribute toward the reductive degradation of DDT in soils and sediments. These new findings further demonstrate the impact that clay materials can have on the natural attenuation of pollutants in natural and artificial systems and open new avenues for the passive treatment of contaminated land.

Description: Fougerite (IMA 2003-057) was accepted by the Commission on New Minerals and Mineral Names of the International Mineralogical Association (IMA) in 2004 as a new mineral to represent the green rust (GR) family. The data on which it was approved, however, are inconsistent. X-ray diffraction patterns from the Fougeres soils contain no peaks that could meaningfully be attributed to a GR phase. The sequential dissolution procedure used to identify GR in the soils was not rigorously tested for selectivity. If indeed it is selective, the results indicate the presence of 40-78% Fe in minerals other than GR. Other Fe-bearing phases were not included in the interpretation of the spectroscopy data that were presented. The data are consistent with the presence of Fe-bearing clays and other silicate minerals. In light of the ambiguous and conflicting data, we recommend that the case for fougerite as a mineral be re-evaluated by the IMA.

Description: Organo-clays are of interest in the modification of anion transport properties in engineered barriers. In the present study, surface charge and wettability were assessed for tracking changes in the effective diffusion coefficient (Deff) by the formation or suppression of bound H2O layers on the external surfaces of clays. Bentonite samples modified with three different organic cations in amounts of 0 to 400% of the cation exchange capacity were used. Diffusive transport was determined in H2O[-〉]D2O exchange experiments in a newly constructed cell adapted to the attenuated total reflectance (ATR) accessory of a Fourier-transform infrared (FTIR) spectrometer at two different dry bulk densities and various degrees of water saturation. All organo-clay combinations showed changes in surface charge after the addition of organic cations, from a negative value of 99 mmolc/kg for the original bentonite to a maximum positive value of 230.5 mmolc/kg for hexadecylpyridinium (HDPy)-montmorillonite. The positive charge resulted from adsorption of the organic cation in excess of the CEC. Hydrophobic surface properties with contact angles 〉90{degrees} were obtained for HDPy-montmorillonite samples with monolayers of organic cations on the external surfaces only. Here, where hydrophobicity suppressed the formation of bound H2O layers, the largest Deff of 2.7x10-10 m2/s was observed in the high dry bulk density range (1.0-1.5 g/cm3) under water-saturated conditions. In the low dry bulk density range (0.6-0.9 g/cm3) this effect was weakened significantly because, with increasing pore size, the effect of bound H2O layers was reduced. In the high dry bulk density range at partial water saturation (40%), diffusive transport was hindered by the small water volume. Previous work found that, in the high dry bulk density range and water-saturated state, Deff was 2.4x10-11 m2/s for the original bentonite. Deff for all hydrophilic organo-clay samples was [≤]2.1x10-11 m2/s, somewhat less than for the hydrophobic sample. In hydrophilic organo-clay samples, retardation factors that retard the value for Deff, up to a magnitude of 0.5, include an increase in dry bulk density and a decrease in water saturation. In the water-saturated state at high dry bulk densities, hydrophobic surface properties suppressing the formation of bound H2O layers can increase Deff by one order of magnitude.

Description: Electron energy-loss spectroscopy (EELS), energy-filtered transmission electron microscopy (EFTEM), and high-resolution transmission electron microscopy (HRTEM) have been applied in mineralogy and materials research to determine the oxidation states of various metals at high spatial resolution. Such information is critical in understanding the kinetics and mechanisms of mineral-microbe interactions. To date, the aforementioned techniques have not been applied widely in the study of such interactions. In the present study, the three techniques above were employed to investigate mineral transformations associated with microbial Fe(III) reduction in magnetite. Shewanella putrefaciens strain CN32, a dissimilatory metal-reducing bacterium, was incubated with magnetite as the sole electron acceptor and lactate as the electron donor for 14 days under anoxic conditions in bicarbonate buffer. The extent of bioreduction was determined by wet chemistry and mineral solids were investigated by HRTEM, EFTEM, and EELS. Magnetite was partially reduced and biogenic siderite formed. The elemental maps of Fe, O, and C and red-green-blue (RGB) composite map for residual magnetite and newly formed siderite were contrasted by the EFTEM technique. The HRTEM revealed nm-sized magnetite crystals coating bacterial cells. The Fe oxidation state in residual magnetite and biogenic siderite was determined using the EELS technique (the integral ratio of L3 to L2). The integral ratio of L3 to L2 for magnetite (6.29) and siderite (2.71) corresponded to 71% of Fe(III) in magnetite, and 24% of Fe(III) in siderite, respectively. A chemical shift (~1.9 eV) in the Fe-L3 edge of magnetite and siderite indicated a difference in the oxidation state of Fe between these two minerals. Furthermore, the EELS images of magnetite (709 eV) and siderite (707 eV) were extracted from the electron energy-loss spectra collected, ranging from 675 to 755 eV, displaying different oxidation states of Fe in the magnetite and siderite phases. The results demonstrate that EELS is a powerful technique for studying the Fe oxidation-state change as a result of microbial interaction with Fe-containing minerals.

Description: Mesoporous materials with pore diameters in the range 2-50 nm forming tubular or fibrous structures are of great interest due to their unique properties. Because they are commonly used as sorbents and catalyst carriers, knowledge of their surface area and porosity is critical. A modified intercalation/ deintercalation method was used to increase the efficiency of nanotube formation from kaolin-group minerals which differ in terms of their degree of structural order. Unlike previous experiments, in the procedure adopted in the present study, methanol was used instead of 1,3-butanediol for grafting reactions and octadecylamine intercalation was also performed. The samples were examined using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and transmission electron microscopy (TEM). The specific surface area and porosity of previously described and newly formed materials were investigated by N2 adsorption/desorption. Compared to results described earlier, the percent yield of nanotubes obtained in the present study was significantly greater only in the case of Maria III' kaolinite, which has high structural order. This increase was obtained mainly by the grafting reaction with methanol. Highly ordered stacking of kaolinite-methanol intercalates was noticed and, thus, the amine intercalation was more efficient. In particular, the use of long-chain octadecylamine significantly increased the nanotube yield. The grafting reaction with methanol procedure yielded fewer nanotubes, however, when applied to poorly ordered samples ( Jaroszow' kaolinite and Dunino' halloysite). In the case of the Maria III' kaolinite, the diameter of the rolled layers observed by TEM was ~30 nm and corresponded to average diameters of newly formed pores (DmN) determined using N2 adsorption/desorption, confirming that nanotubes contributed to an increase in surface area and total pore volume. In the case of Jaroszow' kaolinite and Dunino' halloysite mainly macropores (DmN 〉 100 nm) and mesopores (20 nm 〉 DmN 〉 40 nm) were formed. The pores were attributed to interparticle and interaggregate spaces in the stacks of platy particles and to the small relative number of nanotubes.

Description: Magnetite (Fe3O4) is a key economically valuable component in iron ore and is extracted by dissolution processes, but among the Fe (oxyhydr)oxides its solubility behavior is one of the least understood. The objective of this study was to improve understanding of magnetite dissolution mechanisms leading to thermodynamic equilibrium by comparing the dissolution of two solid samples, one synthetic and one industrial, using oxalic, sulfuric, and nitric acids at varying concentrations and temperatures. Of the three solid-liquid systems investigated, only the system consisting of magnetite and oxalic acid reached an equilibrium state within the duration of an individual experiment (6 h). In this system, increasing the acid concentration resulted in a significant increase in the equilibrium concentration of dissolved Fe. When dissolving synthetic and industrial magnetite, increasing the temperature not only increased the rate of reaction but also affected the concentration of dissolved Fe. Significant effects were observed when increasing the temperature from 15 to 35{degrees}C, but only slight differences were seen on further increases in temperature. Observations regarding the equilibrium state of the sulfuric and nitric acid systems could not be made because equilibrium was not reached. The most important individual observation regarding the equilibrium state of the nitric- and sulfuric-acid systems seems to be that in future studies a much longer reaction time is necessary, due to slow kinetics of the dissolution mechanism. A proton-based mechanism has been hypothesized as the one governing the dissolution of magnetite by these two acids, but only the dissolution of the industrial sample yielded results that were similar for these two acids and consistent with that hypothesis.

Description: Clay processes, mineral reactions, and element budgets in oceans continue to be important topics for scientific investigation, particularly with respect to understanding better the roles of chemistry, formation mechanism, and input from hydrothermal fluids, seawater, and non-hydrothermal mineral phases. To that end, the present study was undertaken. Three samples of submarine metalliferous sediments of hydrothermal origin were studied to investigate the formation of smectite, usually Fe-rich, which takes place in such environments. The samples are from the historical collection returned by the British HMS Challenger expedition (1872-1876) and kept at the Natural History Museum in London. The samples were collected from the vicinity of the Pacific-Antarctic Ridge and the Chile Ridge. The samples were analyzed by means of X-ray diffraction (XRD), chemical analysis, scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX), infrared (IR), and transmission electron microscopy-analytical electron microscopy (TEM-AEM). After removal of biogenic calcite the samples appeared to consist mainly of two low-crystallinity phases mixed intimately: Fe/Mn (oxyhydr)oxides and a Si-Al-Mg-Fe phase of similar chemical characteristics to smectite and with variable proportions of the above elements, as indicated by XRD, IR, and SEM-EDX. In particular, analysis by XRD revealed the presence of highly disordered {delta}-MnO2. The TEM-AEM analysis showed that Fe/MnOOH particles have Fe/Mn ratios in the range 25-0.2 and textures changing from granular to veil-like as the proportion of Mn increased. The smectite-like material has the morphology and chemistry of smectite, as well as 10-15 A lattice fringes. Selected area electron diffraction (SAED) patterns indicated a very poorly crystalline material: in some cases distances between diffraction rings corresponded to d values of smectite. The smectite composition indicated a main Fe-rich dioctahedral component with a substantial Mg-rich trioctahedral component (total octahedral occupancy between 2.02 and 2.51 atoms per O10[OH]2). The (proto-) smectite is interpreted to have formed within the metalliferous sediment, as a slow reaction between Fe/MnOOH, seawater (providing Mg), detrital silicates from the continent (providing Si and Al), and X-ray amorphous silica of hydrothermal origin that adsorbed on Fe/MnOOH phases and deposited with them. This material is possibly in the process of maturation into well crystallized smectite.

Description: Syntheses of Fe-, Co-, and Ni-containing Mg-Al-layered double hydroxides (LDHs) are described here because Fe, Co, and Ni represent the major constituents in steel containers used for storing spent nuclear fuel. Much evidence exists for the formation of LDHs during the corrosion of such containers under repository-relevant conditions. Because of their anion-exchange properties, LDHs can be considered as materials with the potential to retain and immobilize anionic radionuclides. Evaluation of the thermodynamic properties of LDHs is essential for reliable prediction of their behavior (solubility, anion exchange properties) in geochemical environments. The impact on the thermodynamic properties of the isostructural incorporation of divalent cations into the LDH was the main focus of the present study. Mg-Al-Cl-LDH and the Fe-, Co-, and Ni-doped LDHs were synthesized by the co-precipitation method and then characterized (using powder X-ray diffraction (PXRD), extended X-ray absorption fine structure (EXAFS), X-ray absorption near edge structure (XANES), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy energy-dispersive X-ray spectroscopy (SEM-EDX), and thermogravimetric analyses (TGA)). The PXRD and EXAFS analyses indicated that all synthesized samples were pure LDHs where Co, Ni, and Fe were incorporated isostructurally. The EXAFS and XANES results demonstrated that Ni and Co were incorporated as divalent cations and Fe as a trivalent cation. Thermodynamic calculations were performed assuming an equilibrium state between aqueous solutions and corresponding precipitates after synthesis. The first estimates of the molar Gibbs free energies for Fe-, Co-, and Ni-containing LDHs at 70°C were provided. The calculated Gibbs free energy of the pure Mg-Al-LDH (–3629 kJ/mol) was slightly less than those for Fe-, Co-, and Ni-containing compositions (–3612±50, –3604±50, –3593±50kJ/mol).

Description: The present study investigated the anisotropy in the orientation of particles in synthetic swelling clay media prepared from the sedimentation of particle-sized fractions of vermiculite. The different size fractions (〈0.1, 0.1–0.2, 1–2, and 10–20 μm) were chosen because they represent the wide range of particle sizes of swelling clay minerals encountered in natural environments. Small-angle neutron scattering (SANS) and neutron diffraction measurements allowed the characteristic scattering/diffraction features to be derived and the quantitative information about the particle orientation distributions along two directions with respect to the sedimentation plane to be extracted. The results obtained confirmed that the increase in particle size was associated with the development of a random orientation for the particles, whereas the hydration state had a negligible impact on the organization of the porous media. For finer vermiculite particles, the rocking curves demonstrated an anisotropy of the systems that is similar to those reported previously on natural montmorillonite minerals. This result suggests that the location of the layer charge has little or no impact on the anisotropy features of particle orientation. For the coarsest fraction (10–20 μm), quantitative information about the particle orientation revealed that the relative proportion of the isotropic contribution represents up to 85% of the material. The anisotropy in the 2D SANS patterns revealed a pore-network anisotropy that was consistent with the particle size.

Description: In situ thermal recovery methods such as cyclic steam stimulation (CSS) are required to extract highly viscous bitumen from the Clearwater Formation oil sands of Alberta, Canada. The injection of hot fluids during CSS has altered the mineralogy of the sands, resulting in the loss of some minerals ( e.g. disseminated siderite, volcanic glass) and precipitation of others ( e.g. zeolites and abundant hydroxy-interlayered smectite). The high temperatures and high water–rock ratios associated with CSS might also alter the oxygen and hydrogen isotopic compositions of pre-existing clay minerals even in the absence of mineralogical changes. The present study exploits this fact to track the movement of injected hot fluids during CSS. Berthierine, a common diagenetic clay mineral in the Clearwater sands, survived CSS but acquired substantially lower 18 O and 2 H values in cores located ≤10 m from the injection well. In contrast, the oxygen and hydrogen isotopic compositions of berthierine in cores located further from the injection well were generally unaffected, except at the depth of steam injection where horizontal fractures facilitate greater lateral penetration of hot fluids. Smectitic clays in near-injector cores also acquired lower 18 O values during CSS, but a systematic shift in 2 H values was not observed. While hydrogen-isotope exchange undoubtedly occurred, the particular combination of temperature and H isotopic composition of the injected fluid used during CSS appears to have yielded post-steam 2 H values that are indistinguishable from pre-steam values. Only samples from near-injector core G-OB3 that contain hydroxy-interlayered smectite have lower 2 H values as a result of CSS.

Description: Creating an environmentally friendly precursor to form a kaolinite intercalation compound is important for promoting the applications of nanohybrid kaolinite in electrochemical sensors, low- or zero-toxicity drug carriers, and clay-polymer nanocompounds. In the present study, a stable hydrated kaolinite precursor with d 001 = 0.84 nm was prepared successfully by heating the transition phase, the as-prepared kaolinite-hydrazine intercalate, at temperatures between 40 and 70°C. The structure of the hydrated kaolinite was characterized by X-ray diffraction and infrared spectroscopy. The morphology was examined using scanning electron microscopy. The results showed that the hydrated hydrazine of the transition phase was easy to decompose to hydrazines and water molecules in the interlayer at 40–70°C. Hydrazine molecules de-intercalated gradually, and water molecules remained in the ditrigonal holes of the silicate layer with sufficient stability, finally forming the stable 0.84 nm hydrated kaolinite in the system with a success rate of 80–90%. The 0.84 nm hydrated kaolinite may become an excellent precursor for the preparation of other kaolinite intercalates. A degree of intercalation of ~100% was obtained for the kaolinite-ethylene glycol intercalate, and a degree of intercalation of~80% was obtained for the kaolinite-glycine intercalate from the 0.84 nm hydrated kaolinite precursor.

Description: A compositional gap between sepiolite and palygorskite has long been accepted even though they have similar structures, but recent studies found that such a gap does not exist and that the compositional series is continuous between them. If this is true, intergrowths between these two minerals should exist. The purpose of the present study was to demonstrate the existence of sepiolite-palygorskite intergrowths in all possible proportions, in order to establish the compositional links between ideal sepiolite and ideal palygorskite and to define the compositional limits of these two minerals. Sepiolite and palygorskite have similar structures but different chemical compositions: sepiolite is the most trioctahedral and magnesic extreme, while palygorskite is dioctahedral with Al and Mg in its octahedral sheet. The existence of all intermediate compositions between these two pure extremes has led to the definition of the intermediate minerals, Al-sepiolite and Mg-palygorskite, which can have similar chemical composition. The structural relations between the different minerals of the palygorskite–sepiolite series were studied here by powder X-ray diffraction (XRD), and continuous variation in the chemical composition is explained by the existence of intergrowths of sepiolite and palygorskite polysomes forming a continuous polysomatic series. The existence of intergrowths by mixtures of polysomes in modulated structures can be considered in the same way that the mixed-layer minerals in layered structures are considered. The continuous polysomatic series of sepiolite–palygorskite can be expressed by the general formula: [Si 12 Mg 8 O 30 (OH) 4 (OH 2 ) 4 ] y ·[Si 8 O 20 (Mg 2 Fe 2 ) x (Mg 2 Al 2 ) (1– x ) (OH) 2 (OH 2 ) 4 ] (1– y ) · n H 2 O, where sepiolite and palygorskite are the end-members. The y and x values can be calculated using a ternary plot with the oxide contents of the main octahedral cations (Al 2 O 3 , Fe 2 O 3 , and MgO). The proposed model, which is based on the intergrowth of sepiolite and palygorskite polysomes, explains both the variability in the chemical composition and the compositional limit for the identification of these minerals by X-ray diffraction.

Description: Geological disposal is the preferred option for the final storage of high-level nuclear waste and spent nuclear fuel in most countries. The selected host rock may be different in individual national programs for radioactive-waste management and the engineered barrier systems that protect and isolate the waste may also differ, but almost all programs are considering an engineered barrier. Clay is used as a buffer that surrounds and protects the individual waste packages and/or as tunnel seal that seals off the disposal galleries from the shafts leading to the surface. Bentonite and bentonite/sand mixtures are selected primarily because of their low hydraulic permeability in a saturated state. This ensures that diffusion will be the dominant transport mechanism in the barrier. Another key advantage is the swelling pressure, which ensures a self-sealing ability and closes gaps in the installed barrier and the excavation-damaged zone around the emplacement tunnels. Bentonite is a natural geological material that has been stable over timescales of millions of years and this is important as the barriers need to retain their properties for up to 10 6 y. In order to be able to license a final repository for high-level radioactive waste, a solid understanding of how the barriers evolve with time is needed. This understanding is based on scientific knowledge about the processes and boundary conditions acting on the barriers in the repository. These are often divided into thermal, hydraulic, mechanical, and (bio)chemical processes. Examples of areas that need to be evaluated are the evolution of temperature in the repository during the early stage due to the decay heat in the waste, re-saturation of the bentonite blocks installed, build-up of swelling pressure on the containers and the surrounding rock, and degradation of the montmorillonite component in the bentonite. Another important area of development is the engineering aspects: how can the barriers be manufactured, subjected to quality control, and installed? Geological disposal programs for radioactive waste have generated a large body of information on the safety-relevant properties of clays used as engineered barriers. The major relevant findings of the past 35 y are reviewed here.

Description: Halloysite is used for targeted delivery of drugs and other biomolecules. Renewed interest in examination by X-ray diffraction (XRD) to predict the size of particles that can be loaded onto the nanotubes has resulted. Anhydrous halloysite consists of spiraled tubules the length and diameter of which can be determined by measurement using an electron microscope. In spite of ample evidence regarding the spiral structure of halloysite, current programs to evaluate the structure of halloysite nanotubes consider it to be a hollow tube or a cylinder which prevents accurate prediction of its structure and leads to misinformation about the sizes of materials that can be loaded onto the nanotubes. The overall objective of the current study was to derive equations to estimate the structure of halloysite nanotubes which take into consideration its spiral structure. The study of Fourier transform either by electron diffraction or XRD led to the measurement of the spiral thickness and the nature of the spiral. Calculations of the nanotube dimensions may determine the ability of these carriers to allow the mechanical delivery of certain drugs. Here the structure of hydrated halloysite (hollow cylindrical tubes with a doughnut-like cross-section) and anhydrous halloysite (spiraled or helical structure) are described as previously reported in the literature. The Fourier transform of the spiraled structure was selected based on three different kinds of spirals: the Archimedean spiral, the Power spiral, and the Logarithmic spiral. Programs used to define the crystal structure of materials and to calculate the Fourier transform need to take the spiral structure into consideration.

Description: The conventional cauliflower-like shape of magadiite imposes serious limitations on its applications in adsorption, catalysis, ion exchange, etc . To overcome this problem, a method to prepare it with plate-like structures was developed. This novel approach is based on an interface-controlled heterogeneous nucleation process. Zirconia grinding balls with diameters of 2.0 mm were dispersed in the starting solution to provide solid–liquid interfaces. Then the starting solution with a SiO 2 :NaOH:H 2 O molar ratio of 9:2:75 was subjected to hydrothermal treatment at 433 K for 96 h. The presence of the solid–liquid interface improved the crystallization yield and controlled the morphology and specific surface area of the crystals. With the zirconia balls, the yield and sizes of the plate-like magadiite were 52 wt.% and 1–3 μm, respectively. In the absence of zirconia balls, the yield was smaller (45 wt.%) and magadiite shaped like cauliflower was formed. The plate-like magadiite had a specific surface area of 66 m 2 g –1 and a pore-size distribution between 4 and 5 nm, compared with a surface area of 28 m 2 g –1 for the cauliflower-like magadiite. In addition, the plate-like magadiite was a more effective ion exchanger than the cauliflower-like magadiite with a cation exchange capacity of 64.5 mmol/100 g (compared to 53.8 mmol/100 g for the cauliflower-like form) and it had a faster sorption rate for calcium ions.

Description: The present study investigated the use of local and affordable clinoptilolite for the removal of persistent dyes from water. To improve its adsorption capacity, Na-clinoptilolite was modified chemically with two N-terminated siloxanes (molar mass: 2600 and 11000 g/mol) and used to adsorb the dye phenol red. The results of Fourier-transform infrared spectroscopy (FTIR) showed that N-terminated siloxanes were grafted successfully onto clinoptilolite. Examination by X-ray diffraction and scanning electron microscopy supported the suggestion of modifications observed by FTIR. The modified clinoptilolite showed improved adsorption properties for phenol red: up to 0.32 mg of phenol red were removed per g of clinoptilolite modified with N-terminated siloxanes from water, while HCl-treated clinoptilolite removed only 0.15 mg after 4 h. Langmuir and Freundlich models were used to obtain isotherm parameters. Results (with R 2 〉 0.84) from pseudo-first and pseudo-second order equations suggested that adsorption could have involved chemisorption and physisorption, probably because of the mineral-organic nature of the materials prepared.

Description: The early and sensitive detection of microbial contamination of kaolinite slurries is needed for timely treatment to prevent spoilage. The sensitivity, reproducibility, and time required by current methods, such as the dip-slide method, do not meet this challenge. A more sensitive, reproducible, and efficient method is required. The objective of the present study was to develop and validate such a method. The new method is based on the measured growth kinetics of indigenous kaolinite-slurry microorganisms. The microorganisms from kaolinite slurries with different contamination levels were eluted and quantified as colony-forming units (CFUs). Known quantities of E. coli (ATCC 11775) were inoculated into sterilized kaolinite slurries to relate kaolinite-slurry CFUs to true microbial concentrations. The inoculated slurries were subsequently incubated, re-extracted, and microbial concentrations quantified. The ratio of the known inoculated E. coli concentration to the measured concentration was expressed as the recovery efficiency coefficient. Indigenous microbial communities were serially diluted, incubated, and the growth kinetics measured and related to CFUs. Using the new method, greater optical densities (OD) and visible microbial growth were measured for greater dilutions of kaolinite slurries with large microbial-cell concentrations. Growth conditions were optimized to maximize the correlation between contamination level, microbial growth kinetics, and OD value. A Standard Bacterial Unit (SBU) scale with five levels of microbial contamination was designed for kaolinite slurries using the experimental results. The SBU scale was validated using a blind test of 50 unknown slurry samples with various contamination levels provided by the Imerys Company. The validation tests revealed that the new method using the SBU scale was more time efficient, sensitive, and reproducible than the dip-slide method.

Description: The increasing levels of industrial wastewater released to the environment present a serious threat to human health, living resources, and ecological systems. Fe-modified zeolites were developed and tested for removal of Cu 2+ and Zn 2+ from contaminated water. The surfaces of the naturally occurring zeolite, clinoptilolite, were modified with Fe(III) oxyhydroxides using three different methods, denoted I, II, and III (FeCli 1 , FeCli 2 , and FeNaCli 1 , respectively). The oxyhydroxides were prepared in Method I using 0.1 M FeCl 3 ·6H 2 O in an acetate buffer (pH = 3.6); in Method II, using 10% FeCl 3 ·6H 2 O solution in 0.1 M KOH (pH = 10); and Method III was the same as Method I except the clinoptilolite was pretreated with NaCl. Newly synthesized materials from these three methods were then tested for their ability to enhance the sorption capacity for Cu and Zn compared to the natural sample (Cli). Powder X-ray diffraction measurements and the chemical composition of these modified samples confirmed that clinoptilolite maintained its structure while amorphous Fe 3+ species were synthesized. The specific surface area (BET method) of both the natural and modified clinoptilolite increased by 2 and 7.5 times for Methods I and II, respectively. Scanning electron microscopy and energy dispersive X-ray spectroscopy revealed that CaO was formed during Method I (FeCli 1 ). Throughout the adsorption process, the hydrolysis of CaO and the release of OH – caused the precipitation of Cu and Zn hydroxide, which made the determination of the sorption capacity of FeCli 1 impossible. This phenomenon was avoided in Method III (FeNaCli 1 ) because of the absence of exchangeable Ca 2+ . The adsorption experiments with Method II resulted in double-enchanced adsoprtion capacity. Laboratory batch experiments revealed that the sorption capacities increased in the following order: Cli 〈 FeCli 2 〈 FeNaCli 1 , for Cu: 0.121 mmol/g 〈 0.251 mmol/g 〈 0.403 mmol/g and for Zn: 0.128 mmol/g 〈 0.234 mmol/g 〈 0.381 mmol/g.

Description: Reconstructing the origin of bentonitic clays is often a challenging and rather complicated undertaking, but the analysis of certain predictor clay minerals is proving to be an excellent method to simplify this process. The goal of the present investigation was to use abundance changes of five X-ray diffraction (XRD) predictor minerals to determine the relative contributions of weathering and parent-rock changes to the origin of clay minerals in Egyptian bentonitic clays as the test case. The XRD predictor minerals, selected in an earlier discriminant function analysis of quantitative abundances of 14 minerals, provided a simpler approach to the interpretation of clay-mineral origins because they are the minerals that were most responsible for statistically significant differences among the samples. Changes in mineral composition were basically a function of parent-rock lithology, drainage, and climate interactions. A Paleo-Climate Index (CI; the ratio of coarsely crystalline kaolinite to Fe-rich smectite), and a Parent-Rock Index (PI; the ratio of the illitic phases and quartz abundances to pure smectite) were established to track the paleo-climate and parent-rock changes, respectively. Low CI values indicated that a long, seasonally dry climate prevailed during the Middle Eocene, uppermost Eocene, Lower Miocene, and Upper Pliocene bentonitic clay deposition. Lowermost Upper Eocene and the Middle Miocene bentonitic clays were produced when a wet climate prevailed throughout the year. Moderate to high PI values suggested derivation of the clays from the acidic basement crystalline rocks at Uweinat-Bir Safsaf uplift and Lower Paleogene shales during the Middle Eocene and lowermost Upper Eocene. The youngest Upper Eocene and Lower Miocene materials contained abundant Fe-smectite and low PIs indicating derivation from tholeiitic basalts. Diagenetic and sedimentary segregation modifications were not apparent. Direct evidence for in situ derivation from volcanic precursor materials was lacking in general, but volcanic eruptions were common in the region. The minerals in the Egyptian bentonitic clays formed as weathering products on land and have been transported by north-flowing streams and rivers to the sites of accumulation.

Description: A major problem with polymeric membranes is low hydrophilicity and consequently a tendency to fouling. Preparing composite membranes is one way to improve the properties and performance of the neat membrane. In the present study, the effects of coagulation-bath temperature (CBT) and the hydrophilic nanoclay concentration of montmorillonite (MMT) on the morphology and performance of asymmetric cellulose acetate butyrate (CAB) membranes were investigated. The membranes were prepared via phase inversion induced by immersion precipitation in a water-coagulation bath. The morphology of the membranes prepared was studied by scanning electron microscopy (SEM). The permeation performance of the membranes prepared was studied by experiments using pure water and bovine serum albumin (BSA) solutions as feeds. The results showed that the membrane thickness and pure water flux (PWF) were increased by adding up to 2 wt.% MMT nanoclay to the casting solution. These two parameters decreased with further addition of MMT, however. In addition, the results obtained in the case of filtration of BSA solution indicated that the addition of MMT in the casting solution increased permeate flux and reduced BSA rejection slightly. Furthermore, increasing the MMT nanoclay concentration in the casting solution increased pure water flux recovery and consequently decreased the fouling. Decreasing the CBT in the presence of MMT during membrane preparation resulted in the formation of a more porous structure and consequently increased the flux and simultaneously decreased the BSA rejection.

Description: Excavated bentonite from two large iron—bentonite field experiments at Äspö Hard Rock Laboratory in Sweden was investigated with respect to iron redox chemistry and mineralogy. The iron redox chemistry was studied by Fe K-edge X-ray absorption near edge structure spectroscopy and the mineral phases were studied using X-ray diffraction. Bentonite is to be used as a buffer material in high-level radioactive waste repositories to protect the waste containers from their surroundings. Montmorillonite, which is responsible for the sealing properties in the bentonite, is susceptible to redox reactions. A change in the montmorillonite iron redox chemistry may affect its layer charge and hence its properties. The experiments included are the first Alternative Buffer Material test (ABM1) and the Temperature Buffer Test (TBT). The clays were heated to a maximum of ~130°C (ABM1) or ~150°C (TBT) for 2.5 and 7 y, respectively. In the central part of the compacted clay blocks was placed an iron heater and the distance from the heater to the rock was ~10 cm (ABM1) and ~50 cm (TBT), respectively. Eleven different clay materials were included in the ABM1 experiment and five were analyzed here. In the ABM1 experiment, the Fe(II)/Fe(III) ratio was increased in several samples from the vicinity of the heater. Kinetic data were collected and showed that most of the Fe(II)-rich samples oxidized rapidly when exposed to atmospheric oxygen. In the TBT experiment the corrosion products were dominated by Fe(III) and no significant increase in Fe(II) was seen. In ABM1, reducing conditions were achieved, at least in parts of the experiment; in TBT, reducing conditions were not achieved. The difference was attributed to the larger scale of the TBT experiment, providing more oxygen after the installation, and to the longer time taken for water saturation; oxidation of the samples during excavation cannot be ruled out. Minor changes in the bentonite mineral phases were found in some cases where direct contact was made with the iron heater but no significant impact on the bentonite performance in high-level radioactive waste applications was expected as a result.

Description: Supercritical carbon dioxide (scCO 2 ) processing has been proven as a method for preparing polymer/montmorillonite (MMT) nanocomposites with improved platelet dispersion. The influence of scCO 2 processing on the shape and size of the MMT tactoid/platelet, which is of great importance to the final platelet dispersion in the polymer matrix, is scarcely reported in the literature. In the present study, the pristine MMT was first surface modified with 3-glycidoxypropyltrimethoxysilane (the grafted MMT is labeled as GMMT), and then intercalated using three kinds of intercalating agents, myristyltrimethylammonium bromide (MTAB), tetradecyltrihexylphosphonium chloride (TDTHP), and ethoxyltriphenylphosphonium chloride (ETPC), in water or scCO 2 , to study the effect of intercalating agent type and intercalation method on the morphology and thermal properties of GMMT, as a part of a program devoted to the synthesis of polymer/MMT nanocomposites. The structure of intercalated GMMT was characterized by thermogravimetric analysis, X-ray powder diffraction, and scanning electron microscopy (SEM). The optimum intercalation conditions in scCO 2 were established by trying a range of reaction times and pressures. The structures of intercalated GMMT obtained under optimum scCO 2 conditions and water were compared. The basal spacing of GMMT intercalated in scCO 2 was almost the same as that in water, and both were obviously larger than that of GMMT. The GMMT exhibited a compact spherical morphology (examined using SEM), and the surface structures (including surface morphology, surface roughness, and surface compactness) of samples intercalated in water became ‘less compact’ and the degree of the ‘compactness’ of samples intercalated in scCO 2 decreased further. Whether in water or scCO 2 , samples intercalated with TDTHP exhibited a larger basal spacing and the extent of disorder increased compared to that for samples intercalated with MTAB. The pristine MMT was also intercalated for comparison and silane grafting was proven to contribute to the increased basal spacing and ‘less compact’ surface structure.

Description: The collector for separating diasporic bauxite serves as a type of flotation reagent by adsorbing selectively on diaspore to make it hydrophobic enough to separate it from the aluminosilicates. Although the flotation process is considered economical in the desilication of Chinese diasporic bauxite, the existing collectors fail to separate these ores because of their poor adsorption selectivity over other minerals. The present study was an attempt to seek a collector for selective flotation of diaspore over aluminosilicates. A novel carboxyl hydroxamic acid compound, 2,2-bis(hydroxycarbamoyl) decanoic acid (BHDA), was designed and synthesized, and the flotation behavior of diaspore, kaolinite, and illite was investigated by flotation tests with BHDA. The interactions between the BHDA and the minerals were also explored by Fourier-transform infrared spectroscopy (FTIR), zeta-potential measurement, and density functional theory (DFT) calculation. Using BHDA as the collector, the pulp pH value affected the floatability of diaspore significantly while the floatability of kaolinite or illite was unaffected or only slightly affected. The dosage of BHDA had little effect on the floatability of the three minerals. The greatest difference in floatability between diaspore and aluminosilicates occurred at mid-range pulp pH (7). Large shifts in characteristic absorption peaks and new absorption peaks were observed for BHDA-treated diaspore but were absent from BHDA-treated aluminosilicates. The change in the negative zeta potential of diaspore was also greater than those of aluminosilicates in the presence of BHDA. The O atoms in the carboxyl and hydroxycarbamoyl of BHDA have highly negative charges, and favorable stereo conditions existed to form five-or six-membered rings, resulting in their coordination with the Al atoms of diaspore, leading to chemisorption in chelate rings; the adsorption of BHDA on kaolinite or illite, on the other hand, was mainly physical in nature. The BHDA was, therefore, highly selective in the flotation between diaspore and aluminosilicates and possibly suitable for the separation of diasporic bauxite.

Description: Bentonite cake is usually formed on the excavated trench surface that is supported by the bentonite slurry during construction of slurry cutoff walls. The lower hydraulic conductivity of bentonite cakes formed during construction of slurry cutoff walls in comparison to backfill materials provides an additional benefit. In the present study, the hydraulic conductivities of bentonite cakes made using three different bentonites were estimated using the modified fluid-loss test under various pressures. Both the hydraulic conductivities of bentonite cakes and cutoff-wall backfill are important in evaluating the in situ hydraulic performance of slurry cutoff-wall construction. Three bentonite slurry concentrations of 4, 6, and 8% were used to fabricate bentonite cakes that represent common field conditions. X-ray diffraction, cation exchange capacity, and swell-index data were collected to characterize the bentonites. Two modified methods for analyzing fluid-loss test results were used to estimate bentonite cake hydraulic conductivities. In addition, the viscosity as a function of time was measured to explain the sealing capacities of the bentonite slurries. The bentonite-cake hydraulic conductivities ranged from 2.15×10-11 m/s to 2.88×10-10 m/s, which were 10 to 500 times lower than the cutoff wall backfill design. Experimental results for 4 and 6% bentonite slurries were relatively similar, but the 8% slurries were noticeably different. Calculated bentonite-cake thickness and stress distribution indicated that the local void ratio and hydraulic conductivity may vary across the cake thickness. The considerably lower bentonite-cake hydraulic conductivities compared to the cutoff wall backfill design show its significance in slurry cutoff-wall construction practices.

Description: Recognizing weathering effects is significant for any work carried out on glauconites at the surface. The mineralogy and chemistry of glauconite grains exposed to weathering in a hot arid climate for a maximum of 42 y were studied here. The objective of the study was to find the mineralogical and chemical differences between weathered glauconite from the surface and fresh glauconite from the subsurface.One specific glauconite-bearing layer at the surface (Layer 16) of the Abu Tartur phosphate mine, located in the Western Desert of Egypt, was studied in detail and compared to a fresh, subsurface glauconitic sandstone from the underground mine.Even within this single surface layer, the brownish-green glauconite grains vary in color and chemical composition. From top to bottom, the grains show an increase in Fe and K and a decrease in Al and S. In addition, the grains show an internal color zonation caused by variation of Fe and K contents between the center and rim of the grains. The differences in color and chemical composition are even more pronounced between the weathered-glauconite grains from the surface and the fresh glauconite grains from the subsurface which are dark green and enriched in Fe and K.The clay fractions consisted of mixed-layer glauconite (illite)-smectite, with the surface samples containing more expandable smectite (50%) than the subsurface samples (20%). In the charge-distribution diagram for muscovite-pyrophyllite-celadonite, the weathered glauconites at the surface showed a clear trend from smectitic glauconite at the top to illitic glauconite at the bottom of the layer, whereas the fresh subsurface sample plotted exactly in the glauconite field.The color, mineralogy, and chemistry indicate that the surface samples were strongly altered by weathering processes and that glauconite transformed progressively into Fe-rich mixed-layer illite-smectite and then into smectites. Weathering can thus completely reverse the glauconitization process. For any chemical and mineralogical characterization of glauconites at the surface, these weathering effects must be taken into consideration.

Description: The island-arc volcanics situated in the eastern part of the Capîlnas-Techereu nappe (South Apuseni Mountains, Romania) were studied to evaluate the temperature, fluid properties, and mineral chemistry during low-temperature metamorphism. Detailed observations of metamorphic mineral assemblages were conducted using powder X-ray diffraction and electron microprobe. The metamorphism involved albitization of plagioclase feldspar and the formation of mafic phyllosilicates, zeolites, and other hydrous Ca-Al-silicate minerals. Mafic phyllosilicates consisted of transitional dioctahedral-trioctahedral smectites, mixed-layer chlorite-smectite (C/S, 6–96% chlorite), and discrete chlorite. The zeolites were analcime, stilbite ± stellerite, heulandite, laumontite, epistilbite, and mordenite. Also present, as secondary minerals filling amygdales and veins, are prehnite, pumpellyite, and secondary amphibole. Two mineral assemblages were identified which provide important information about metamorphic conditions (temperature, reaction progress, and fluid properties): (1) heulandite + analcime + quartz; and (2) laumontite + albite + quartz + prehnite + pumpellyite ± amphibole. The types of and relations between minerals in the first assemblage suggest the occurrence of low-temperature hydrothermal metamorphism in the zeolite facies at ~125ºC, whereas the second assemblage was metamorphosed at 200ºC. The composition and variability of the mineral assemblages in the study area suggest that, due to slow reaction rates, the low-temperature transformations and mineral assemblages were influenced not only by temperature but also by local rock composition, fluid-rock ratio, and fluid chemistry.

Description: A diapiric intrusion of clays in the Carlentini Formation (Tortonian) was discovered in a quarry at S. Demetrio High (Hyblean Plateau, Sicily, Italy). Seven clay samples were analyzed by different analytical methods, including X-ray powder diffraction (XRD) and Fourier-transform infrared (FTIR) spectroscopy, to determine the composition and mechanism of formation (sedimentary vs. hydrothermal) of these clays. Ferric saponite, carbonates (calcite and traces of ankerite), quartz, pyrite, and zeolites (phillipsite and harmotome) were detected using XRD and FTIR. This mineral assemblage, dominated by Fe-rich saponite, and the abundance of light rare-earth elements (LREE), Eu, fluid-mobile elements (FME 〉 10× primordial mantle: Li, Be, B, As, Sb, Pb, U, Ba, Sr, Cs), and other incompatible elements (Zr = 169 ppm, Nb = 46 ppm, Th = 11 ppm, on average) imply that S. Demetrio clays precipitated from a mixture of hot Si-rich hydrothermal fluids (350–400ºC) and cold seawater. The evidence is in accord with the affinity of clays for hydrothermally modified mafic and ultramafic rocks, forming the Hyblean lower crust, based on multi-element comparisons, and on the occurrence of trace amounts of chrysotile 2Mc1 and sepiolite. The association of long-chain aliphatic-aromatic hydrocarbons (intensity ratios I2927/I2957 〉 0.5) with hydrothermal clays, the lack of fossils, and the similarity of the IR absorption bands with those of organic compounds detected previously in some metasomatized Hyblean gabbroic xenoliths suggest a possible abiogenic origin of hydrocarbons via a Fischer-Tropsch-type reaction. The S. Demetrio clay diapir was emplaced at shallow crustal levels in the Late Miocene as a consequence of the interaction, at a greater depth, of an uprising basalt magma and the products of an early, serpentinite-hosted hydrothermal system.

Description: This study uses the data from Miocene rocks of the Carpathian Foredeep to test the performance of the computer programs QUANTA and BESTMIN in aiding the interpretation of geophysical log data. These programs were designed to help trace trends in the mineral composition of rocks, the chemical composition of minerals, and the effects of these data on petrophysical and geophysical logging parameters. Chemical and X-ray diffraction data for 65 samples of shales, sandstones, and carbonates taken from cored wells in the molasse basin of the Carpathian Foredeep were processed. Compositional differences were detected between rocks sourced from the platform and rocks sourced from the Carpathians. Quartz, K-feldspar, and zircon were more abundant in the coarse-grained rocks (sandstones), while calcite, ankerite, siderite, pyrite, barite, halite, celestite, apatite, anatase, chlorite, 2:1 minerals, and organic matter were more abundant in the fine-grained rocks (shales). Plagioclase reached its maximum in coarse shales. Ankerite, chlorite, and dioctahedral 2:1 minerals had more Fe in the coarse-grained rocks. The dioctahedral 2:1 minerals in fine-grained rocks had a greater concentration of smectitic layers. This information permitted the precise calculation of grain density, porosity, adsorbed water, and some geophysical logging parameters. It also permitted the calibration of well-log response, in particular, the macroscopic neutron absorption cross-section (?a) combined with the photoelectric absorption factor (Pe) or with Pe + Ca (calcium content, measurable in wells by spectroscopic techniques) with porosity and cation exchange capacity (CEC). The NaCl concentration in the pore waters was found to range from the values typical for seawater in shales to the freshwater level in clean sandstones.

Description: Particle concentration, charge, solution chemistry (i.e. ionic strength), and the nature of organic matter (OM) are the major factors controlling particle flocculation in aqueous environments. In the present study, the nature of clay fabric associated with clay–OM interaction at a range of ionic strengths was the focus. In the flocculation experiments, the aqueous suspension of montmorillonite and chitin was mixed with NaCl/MgSO4 electrolyte solution. Advanced sample-preparation techniques and visualization methods using transmission electron microscopy were used to observe directly the micro- and nano-scale clay–OM fabric of the resulting flocs. Such direct observation elucidated the role of OM in clay flocculation; few attempts have been made in the past due to the technical difficulties in preserving the original structure. A comparison of clay fabric at two different ionic strengths of 0 and 0.14 M revealed that the individual hexagonal clay particles settled slowly with little intra-aggregate void space (void ratio: 0.07) at 0 M while rapid flocculation and settling of clay particles at 0.14 M, with or without OM, resulted in a more open fabric with greater void space (void ratio: 0.33). The silver-staining technique demonstrated effectively the location of electron-transparent chitin in montmorillonite aggregates. Chitin appeared to link the face-to-face (FF) contacts of clay domains by bridging between negatively charged face surfaces. However, the resultant void ratio and the average hydrodynamic diameter (dH) values were lower than in the OM-free system after flocculation. The results indicated that the interplay between ionic strength and OM content affected the floc architecture and void ratio.

Description: Microwave irradiation as a means for heating bentonites during acid activation has been investigated in the past but it has never been optimized for industrial applications. The purpose of this study was to apply a factorial 23 experimental design to a Serbian bentonite in order to determine the influence of microwave heating on the acid-activation process. The effect of acid activation under microwave irradiation on the textural and structural properties of bentonite was studied as a model reaction. A mathematical, second-order response surface model (RSM) was developed with a central composite design that incorporated the relationships among various process parameters (time, acid concentration, and microwave heating power) and the selected process response of specific surface area of the bentonite. The ranges of values for the process parameters chosen were: time, 5–21 min; acid concentration, 2–7 M; and microwave heating power, 63–172 W. The effect of individual variables and their interaction effects on the textural and structural properties of the bentonite were determined. Statistical analysis showed that the duration of microwave irradiation was less significant than the other two factors. The model showed that increasing the time and acid concentration improved the textural properties of bentonites, resulting in increased specific surface area. This model is useful for setting an optimum value of the activation parameters for achieving the maximum specific surface area. An optimum specific surface area of 142 m2g-1 was achieved with an acid concentration of 5.2 M, activation time of 7.4 min, and microwave power of 117 W.

Description: Contaminant-transport modeling requires information about the charge of subsurface particle surfaces. Because values are commonly reused many times in a single simulation, small errors can be magnified greatly. Goethite ({alpha}-FeOOH) and pyrolusite ({beta}-MnO2) are ubiquitous mineral phases that are especially contaminant reactive. The objective of the present study was to measure and compare the point of zero charge (PZC) using different methods. The pyrolusite PZC was measured with three methods: mass titration (MT) (PZC = 5.9{+/-}0.1), powder addition (PA) (PZC = 5.98{+/-}0.08), and isoelectric point, IEP (PZC = 4.4{+/-}0.1). The IEP measurement was in agreement with literature values. However, MT and PA resulted in a statistically larger PZC than the IEP measurement. The surface area of pyrolusite, 2.2 m2g-1, was too small to permit PZC determination by the potentiometric titration (PT) method. Goethite PZC values were measured using MT (7.5{+/-}0.1), PT (7.46{+/-}0.09), and PA (7.20{+/-}0.08). The present work presents the first reported instance where MT and PA have been applied to measure the point of zero charge of either pyrolusite or goethite. The results illustrate the importance of using multiple, complementary techniques to measure PZC values accurately.

Description: The swelling property of smectite is dominated by the hydration of exchangeable cations in the interlayer spacing ( interlayer hydration'). By investigating systematically the swelling behavior of various exchangeable cations with different valences and ionic radii, the interlayer hydration of smectite was explored. The swelling behavior of Li+-, K+-, Rb+-, Cs+-, Mg2+-, Sr2+-, Ba2+-, and La3+-montmorillonites in undersaturated conditions was measured precisely over the range 50-150{degrees}C by in situ X-ray diffraction (XRD) analyses. The systematic swelling behavior of ten homocationic montmorillonites, the aforementioned eight homoionic montmorillonites, plus Na+ and Ca2+ from a previous study, and the cation hydration energies were analysed by studying the changes occurring in the basal spacing and the 001 peak width. With decreasing cation hydration energy, swelling curves (i.e. plots of basal spacing vs. relative humidity (RH)) change from continuous (Mg2+, La3+, and Ca2+) to stepwise (Sr2+, Li+, Ba2+, and Na+) to one-layer only (K+, Rb+, and Cs+). For the first two groups, the RH at the midpoint between the one- and two-layer hydration states increased as the cation hydration energy decreased. Under low RH, with increasing temperature, the basal spacings of Mg-, La-, Ca-, Sr-, Li-, and Ba-montmorillonites decreased continuously to the zero-layer hydration state, whereas Na-, K-, Rb-, and Cs-montmorillonites swelled from the zero-layer hydration state even at the lowest temperature (50{degrees}C). A decrease in the basal spacing at the same RH but at different temperatures suggests the existence of metastable states or that the layer-stacking structure changes with temperature. The systematics of the swelling behavior of various homocationic montmorillonites as functions of RH and temperature (

Description: Electron energy-loss spectroscopy (EELS), energy-filtered transmission electron microscopy (EFTEM), and high-resolution transmission electron microscopy (HRTEM) have been applied in mineralogy and materials research to determine the oxidation states of various metals at high spatial resolution. Such information is critical in understanding the kinetics and mechanisms of mineral-microbe interactions. To date, the aforementioned techniques have not been applied widely in the study of such interactions. In the present study, the three techniques above were employed to investigate mineral transformations associated with microbial Fe(III) reduction in magnetite. Shewanella putrefaciens strain CN32, a dissimilatory metal-reducing bacterium, was incubated with magnetite as the sole electron acceptor and lactate as the electron donor for 14 days under anoxic conditions in bicarbonate buffer. The extent of bioreduction was determined by wet chemistry and mineral solids were investigated by HRTEM, EFTEM, and EELS. Magnetite was partially reduced and biogenic siderite formed. The elemental maps of Fe, O, and C and red-green-blue (RGB) composite map for residual magnetite and newly formed siderite were contrasted by the EFTEM technique. The HRTEM revealed nm-sized magnetite crystals coating bacterial cells. The Fe oxidation state in residual magnetite and biogenic siderite was determined using the EELS technique (the integral ratio of L3 to L2). The integral ratio of L3 to L2 for magnetite (6.29) and siderite (2.71) corresponded to 71% of Fe(III) in magnetite, and 24% of Fe(III) in siderite, respectively. A chemical shift (~1.9 eV) in the Fe-L3 edge of magnetite and siderite indicated a difference in the oxidation state of Fe between these two minerals. Furthermore, the EELS images of magnetite (709 eV) and siderite (707 eV) were extracted from the electron energy-loss spectra collected, ranging from 675 to 755 eV, displaying different oxidation states of Fe in the magnetite and siderite phases. The results demonstrate that EELS is a powerful technique for studying the Fe oxidation-state change as a result of microbial interaction with Fe-containing minerals.

Description: Most natural and synthetic rubbers have inherently high flammability, a property which limits their uses. The aim of the present work was to study the effect of organo-montmorillonite (OMMT) and modified OMMT on the flame-retardance and mechanical properties of natural rubber (NR) composites. The OMMT was modified with hyper-branched polymer via condensation polymerization between the intercalation agent, N,N-di(2-hydroxyethyl)-N-dodecyl-N-methylammonium chloride, and the monomer, N,N-dihydroxyl-3-aminomethyl propionate. This modified OMMT was then reacted with phosphate, and a novel flame-retardant hyper-branched organic montmorillonite (FR-HOMMT) was thus obtained. The surface morphology, interlayer space, interlamellar structure, and thermal properties of these modified clays were investigated by Fourier-transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction, and thermogravimetric analysis. The FR-HOMMT showed increased basal spacing and better thermal stabilities due to the different arrangement and thermal stability of the novel organic macromolecular surfactant. Natural rubber NR/OMMT and NR/FR-HOMMT composites were prepared by conventional compounding with OMMT and the phosphorus-based organo-montmorillonite. The cure characteristics, tensile strength, wear resistance, thermal stabilities, and flame-retardant properties were researched and compared. The best dispersion of this modified clay was observed for 20 phr (parts per hundred of rubber) of FR-HOMMT-filled composite, which resulted in the best mechanical performance with an increase of 47% in tensile strength, of 40% in elongation at break, and decrease of 140% in abrasion loss compared with 20 phr of the OMMT-filled matrix. A mechanism for reinforcing and flame retardance is proposed here. The ‘anchor’ effect caused by the hyper-branched polymer may decrease the number and size of the voids in the NR matrix, and thus increase the crack path during tensile drawing. Meanwhile, the flame retardance of the OMMT and the phosphate may increase the number of carbonaceous layers, thus inhibiting the degree of pyrolysis of the NR matrix during burning.

Description: Landfill leachate is one of the most difficult effluents with which to deal from an environmental perspective because of its concentration and complex composition, including refractory and toxic components such as heavy metals or xenobiotic organic compounds. The objective of the present study was to use organically modified bentonite (OMB) to dispose of landfill leachate 〉10 y old. The OMB was synthesized using a new method, which removed four steps (filtering, washing, drying, and grinding) from the traditional process. After treatment using OMB, the chemical oxygen demand concentration (COD concentration, an index of the organic pollutants in the landfill leachate, was determined using the potassium dichromate method) of the landfill leachate sample decreased from 2400 to 245 mg/L in 5 h, i.e. the organic pollutants reduction efficiency was as high as 90%. Gas chromatography-mass spectrometry results indicated that most of the organic compounds were removed during the process. The modified and unmodified bentonite contained in the OMB deal with the hydrophobic and hydrophilic organic pollutants, respectively, resulting in significant degradation of the leachate. The study results have provided a new cost-effective method for treatment of landfill leachate.

Description: Pillared clays (PILCs) with magnetic properties have significant potential for application in industry and the environment, but relatively few studies of these types of materials have been carried out. The aim of the present work was to gain insight into the magnetic and structural properties of pillared clays by examining in detail the influence of the calcination temperature and the nature of different pillared clays on these properties.Magnetic layered systems from different pillared clays were prepared and characterized. Firstly, Ti-, Al-, and Zr-pillared clays (Ti-PILCs, Al-PILCs, and Zr-PILCs, respectively) were produced at different calcination temperatures and then magnetic pillared clays (Ti-M-PILCs, Al-M-PILCs, and Zr-M-PILCs) were prepared at ambient temperature. The synthesis involves a reduction in aqueous solution of the original Fe-exchanged pillared clay using NaBH4. The structural properties of pillared clays and their magnetic forms were investigated using X-ray diffraction, N2 adsorption, cation exchange capacity determination, and X-ray fluorescence (XRF) measurements. The properties of the magnetic pillared clays were investigated by superconducting quantum interference devices and Mössbauer spectroscopy. An evaluation of the data obtained allowed an estimation of the pillared structure in one PILC-model before and after magnetization. The model was determined on the basis of a simple geometric model and experimental data leading to the calculation of a filling factor (FF) which contained information about the number of intercalated pillared layers and the unaffected layers. In the case of Ti precursors, the best calcination temperature was 400ºC, which maintained the highest specific surface area and pore volume with magnetic parameters suitable for magnetic application. Similar experiments with Al- and Zr-pillars have been discussed. A correlation between the XRF data, porosity, FF calculation, and magnetic properties led to the conclusion that the sample Al-M-PILC previously calcined at 500ºC was the most stable material after the magnetization process. The same examination in the case of Zr materials suggested that the most stable sample had been calcined at 300ºC (sample Zr-M-PILC-300).

Description: The effect of exposure to repository-like conditions on compacted Wyoming bentonite was determined by comparing the hydraulic, mechanical, and mineralogical properties of samples from the bentonite buffer of the Canister Retrieval Test (CRT) with those of reference material. The CRT, located at the Swedish Äspö Hard Rock Laboratory (HRL), was a full-scale field experiment simulating conditions relevant for the Swedish, so called KBS-3, concept for disposal of high-level radioactive waste in crystalline host rock. The compacted bentonite, surrounding a copper canister equipped with heaters, had been subjected to heating at temperatures up to 95ºC and hydration by natural Na-Ca-Cl type groundwater for almost 5 y at the time of retrieval.Under the thermal and hydration gradients that prevailed during the test, sulfate in the bentonite was redistributed and accumulated as anhydrite close to the canister. The major change in the exchangeable cation pool was a loss in Mg in the outer parts of the blocks, suggesting replacement of Mg mainly by Ca along with the hydration with groundwater. Close to the Cu canister, small amounts of Cu were incorporated into the bentonite. A reduction of strain at failure was observed in the innermost part of the bentonite buffer, but no influence was noted on the shear strength. No change in swelling pressure was observed, while a modest decrease in hydraulic conductivity was found for the samples with the highest densities. No coupling was found between these changes in the hydro-mechanical properties and the montmorillonite – the X-ray diffraction characteristics, the cation exchange properties, and the average crystal chemistry of the Na-converted