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  • 1
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    Minerals, Vol. 8, Pages 309: Determination of Dissolution Rates of Ag Contained in Metallurgical and Mining Residues in the S2O32−-O2-Cu2+ System: Kinetic Analysis (2018)
    MDPI Publishing
    In: Minerals
    Details
    Publication Date: 2018-07-24
    Description: Minerals, Vol. 8, Pages 309: Determination of Dissolution Rates of Ag Contained in Metallurgical and Mining Residues in the S2O32−-O2-Cu2+ System: Kinetic Analysis Minerals doi: 10.3390/min8070309 Authors: Julio C. Juárez Tapia Francisco Patiño Cardona Antonio Roca Vallmajor Aislinn M. Teja Ruiz Iván A. Reyes Domínguez Martín Reyes Pérez Miguel Pérez Labra Mizraim U. Flores Guerrero The materials used to conduct kinetic study on the leaching of silver in the S2O32−-O2-Cu2+ system were mining residues (tailings) from the Dos Carlos site in the State of Hidalgo, Mexico, which have an estimated concentration of Ag = 71 g∙ton−1. The kinetic study presented in this paper assessed the effects of the following variables on Ag dissolution rate: particle diameter (d0), temperature (T), copper concentration [Cu2+], thiosulfate concentration [S2O32−], pH, [OH−], stirring rate (RPM), and partial pressure of oxygen (PO2). Temperature has a favorable effect on the leaching rate of Ag, obtaining an activation energy (Ea) = 43.5 KJ∙mol−1 in a range between 288 K (15 °C) and 328 K (55 °C), which indicates that the dissolution reaction is controlled by the chemical reaction. With a reaction order of n = 0.4, the addition of [Cu2+] had a catalytic effect on the leaching rate of silver, as opposed to not adding it. The dissolution rate is dependent on [S2O32−] in a range between 0.02 mol·L−1 and 0.06 mol·L−1. Under the studied conditions, variables d0, [OH−] and RPM did not have an effect on the overall rate of silver leaching.
    Electronic ISSN: 2075-163X
    Topics: Geosciences
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  • 2
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    Minerals, Vol. 7, Pages 16: Influence of Temperature on the Formation of Ag Complexed in a S2O32−–O2 System (2017)
    MDPI Publishing
    In: Minerals
    Details
    Publication Date: 2017-01-28
    Description: Metallic elements of higher economic value, occurring in the mineralogy of Zimapán, are Pb, Zn, Cu, and Fe; said elements are sold as concentrates, which, even after processing, generally include significant concentrations of Mo, Cd, Sb, Ag, and As that can be recovered through different leaching methods. In this work, the influence of temperature in the complexation of silver contained in a concentrate of Zn using the technology of thiosulfate with oxygen injection was studied. Chemical and mineralogical characterization of the mineral concentrate from the state of Hidalgo, Mexico confirmed the existence of silver contained in a sulfide of silver arsenic (AgAsS2) by X-ray Diffraction (XRD). The results obtained by Atomic Absorption Spectrophotometry (AAS) reported abundant metallic contents (% w/w) (48% Zn, 10.63% Fe, 1.97% Cu, 0.84% Pb, 0.78% As, and 0.25% Ag). These results corroborate the presence of metallic sulfides such as pyrite, chalcopyrite, and wurtzite; this last species was identified as the matrix of the concentrate by X-ray Diffraction (XRD) and Scanning Electron Microscopy-Energy-Dispersive X-ray Spectroscopy (SEM-EDS). Pourbaix diagrams were constructed for the AgAsS2–S2O32−–O2 system at different temperatures, which allowed the chemical reaction of leaching to be established, in addition to determining Eh-pH conditions in which to obtain silver in solution. The highest recoveries of the precious metal (97% Ag) were obtained at a temperature of 333 K and [S2O32−] = 0.5 M. The formation of silver dithiosulfate complex (Ag(S2O3)23−) was confirmed by the characterization of the leach liquors obtained from the experiments performed in the temperature range of 298 to 333 K using Fourier transform infrared spectroscopy (FTIR).
    Electronic ISSN: 2075-163X
    Topics: Geosciences
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  • 3
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    Sustainability, Vol. 8, Pages 718: Home Garden Ecosystem Services Valuation through a Gender Lens: A Case Study in the Catalan Pyrenees (2016)
    MDPI Publishing
    Details
    Publication Date: 2016-07-28
    Description: Ecosystem services have become a critical issue in the environmental literature, however knowledge on whether women and men similarly value ecosystem services is still nascent. We aim at advancing the understanding of the relation between gender and environmental perceptions through the analysis of values assigned by women and men to ecosystem services supplied by home gardens in Vall Fosca (Catalan Pyrenees, north-eastern Spain). We found that women give a higher value than men to all ecosystem services. Overall, women’s valuation of the full range of ecosystem services provided by home gardens was 7.55% higher than men’s valuation. Gender socialization influences the way people interact with and value the environment, including highly managed environments such as home gardens. We argue that considering gendered differences in ecosystem services valuation may lead to policies more effective in enhancing ecosystem services provision.
    Electronic ISSN: 2071-1050
    Topics: Energy, Environment Protection, Nuclear Power Engineering
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  • 4
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    Forests, Vol. 7, Pages 146: City “Green” Contributions: The Role of Urban Greenspaces as Reservoirs for Biodiversity (2016)
    MDPI Publishing
    In: Forests
    Details
    Publication Date: 2016-07-16
    Description: Urbanization poses important environmental, social, and ecological pressures, representing a major threat to biodiversity. However, urban areas are highly heterogeneous, with some greenspaces (e.g., urban forests, parks, private gardens) providing resources and a refuge for wildlife communities. In this study we surveyed 10 taxonomic groups to assess their species richness and composition in six greenspaces that differ in size, location, management, and human activities. Species richness differed among taxonomic groups, but not all differed statistically among the studied greenspaces (i.e., sac fungi, bats). Plants, basidiomycetous and sac fungi, and birds showed intermediate assemblage composition similarity (〈54%). The composition of assemblages of copro-necrophagous beetles, grasshoppers, amphibians, and bats was related to the specific traits of greenspaces, mainly size and location. The species richness contribution of each greenspace considering all studied taxonomic groups was highest in the largest greenspace that is located at the southeastern border of the city, while the lowest contribution was recorded in the smallest ones, all of them closer to the city’s center. Our results shed some light on the way in which different taxonomic groups respond to an array of neotropical urban greenspaces, providing an important basis for future studies.
    Electronic ISSN: 1999-4907
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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  • 5
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    Forests, Vol. 7, Pages 163: Functional Diversity of Small and Large Trees along Secondary Succession in a Tropical Dry Forest (2016)
    MDPI Publishing
    In: Forests
    Details
    Publication Date: 2016-07-31
    Description: Functional Diversity is considered an important driver of community assembly in environmental and successional gradients. To understand tree assembly processes in a semideciduous tropical forest, we analyzed the variation of Functional Richness (FRic), Functional Divergence (FDiv), and Functional Evenness (FEve) of small vs. large trees in relation to fallow age after slash-and-burn agriculture and topographical position (flat sites vs. hills). FRic of small trees was lower than null model predicted values across the successional gradient, and decreased unexpectedly in older successional ages. FRic of large trees was higher than null model predictions early in succession and lower in late-successional stands on hills. Dominant species were more similar (low FDiv) in early and intermediate successional stands for small trees, and on hills for large trees, suggesting that species that are best adapted to harsh conditions share similar traits. We also found evidence of competitive exclusion among similar species (high FEve) for small trees in early successional stands. Overall, our results indicate that community assembly of small trees is strongly affected by the changing biotic and abiotic conditions along the successional and topographical gradient. For large trees, hills may represent the most stressful conditions in this landscape.
    Electronic ISSN: 1999-4907
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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  • 6
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    Entropy, Vol. 16, Pages 5796-5809: Global Stability Analysis of a Curzon–Ahlborn Heat Engine under Different Regimes of Performance (2014)
    MDPI Publishing
    In: Entropy
    Details
    Publication Date: 2014-11-05
    Description: We present a global stability analysis of a Curzon–Ahlborn heat engine considering different regimes of performance. The stability theory is used to construct the Lyapunov functions to prove the asymptotic stability behavior around the steady state of internal temperatures. We provide a general analytic procedure for the description of the global stability by considering internal irreversibilities and a linear heat transfer law at the thermal couplings. The conditions of the global stability are explored for three regimes of performance: maximum power (MP), efficient power (EP) and the so-called ecological function (EF). Moreover, the analytical results were corroborated by means of numerical integrations, which fully validate the properties of the global asymptotic stability.
    Electronic ISSN: 1099-4300
    Topics: Chemistry and Pharmacology , Physics
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  • 7
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    Sensors, Vol. 16, Pages 332: Developing an Ear Prosthesis Fabricated in Polyvinylidene Fluoride by a 3D Printer with Sensory Intrinsic Properties of Pressure and Temperature (2016)
    MDPI Publishing
    In: Sensors
    Details
    Publication Date: 2016-03-05
    Description: An ear prosthesis was designed in 3D computer graphics software and fabricated using a 3D printing process of polyvinylidene fluoride (PVDF) for use as a hearing aid. In addition, the prosthesis response to pressure and temperature was observed. Pyroelectric and piezoelectric properties of this ear prosthesis were investigated using an astable multivibrator circuit, as changes in PVDF permittivity were observed according to variations of pressure and temperature. The results show that this prosthesis is reliable for use under different conditions of pressure (0 Pa to 16,350 Pa) and temperature (2 °C to 90 °C). The experimental results show an almost linear and inversely proportional behavior between the stimuli of pressure and temperature with the frequency response. This 3D-printed ear prosthesis is a promising tool and has a great potentiality in the biomedical engineering field because of its ability to generate an electrical potential proportional to pressure and temperature, and it is the first time that such a device has been processed by the additive manufacturing process (3D printing). More work needs to be carried out to improve the performance, such as electrical stimulation of the nervous system, thereby extending the purpose of a prosthesis to the area of sensory perception.
    Electronic ISSN: 1424-8220
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
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  • 8
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    Materials, Vol. 9, Pages 30: Facile Synthesis of SrCO3-Sr(OH)2/PPy Nanocomposite with Enhanced Photocatalytic Activity under Visible Light (2016)
    MDPI Publishing
    In: Materials
    Details
    Publication Date: 2016-01-07
    Description: Pyrrole monomer was chemically polymerized onto SrCO3-Sr(OH)2 powders to obtain SrCO3-Sr(OH)2/polypyrrole nanocomposite to be used as a candidate for photocatalytic degradation of methylene blue dye (MB). The material was characterized by Fourier transform infrared (FTIR) spectroscopy, UV/Vis spectroscopy, and X-ray diffraction (XRD). It was observed from transmission electronic microscopy (TEM) analysis that the reported synthesis route allows the production of SrCO3-Sr(OH)2 nanoparticles with particle size below 100 nm which were embedded within a semiconducting polypyrrole matrix (PPy). The SrCO3-Sr(OH)2 and SrCO3-Sr(OH)2/PPy nanocomposites were tested in the photodegradation of MB dye under visible light irradiation. Also, the effects of MB dye initial concentration and the catalyst load on photodegradation efficiency were studied and discussed. Under the same conditions, the efficiency of photodegradation of MB employing the SrCO3-Sr(OH)2/PPy nanocomposite increases as compared with that obtained employing the SrCO3-Sr(OH)2 nanocomposite.
    Electronic ISSN: 1996-1944
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 9
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    IJERPH, Vol. 13, Pages 117: Heat and Humidity in the City: Neighborhood Heat Index Variability in a Mid-Sized City in the Southeastern United States (2016)
    MDPI Publishing
    Details
    Publication Date: 2016-01-12
    Description: Daily weather conditions for an entire city are usually represented by a single weather station, often located at a nearby airport. This resolution of atmospheric data fails to recognize the microscale climatic variability associated with land use decisions across and within urban neighborhoods. This study uses heat index, a measure of the combined effects of temperature and humidity, to assess the variability of heat exposure from ten weather stations across four urban neighborhoods and two control locations (downtown and in a nearby nature center) in Knoxville, Tennessee, USA. Results suggest that trees may negate a portion of excess urban heat, but are also associated with greater humidity. As a result, the heat index of locations with more trees is significantly higher than downtown and areas with fewer trees. Trees may also reduce heat stress by shading individuals from incoming radiation, though this is not considered in this study. Greater amounts of impervious surfaces correspond with reduced evapotranspiration and greater runoff, in terms of overall mass balance, leading to a higher temperature, but lower relative humidity. Heat index and relative humidity were found to significantly vary between locations with different tree cover and neighborhood characteristics for the full study time period as well as for the top 10% of heat index days. This work demonstrates the need for high-resolution climate data and the use of additional measures beyond temperature to understand urban neighborhood exposure to extreme heat, and expresses the importance of considering vulnerability differences among residents when analyzing neighborhood-scale impacts.
    Print ISSN: 1661-7827
    Electronic ISSN: 1660-4601
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Medicine
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  • 10
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    Forests, Vol. 6, Pages 4573-4587: The Influence of Stocking and Stand Composition on Productivity of Boreal Trembling Aspen-White Spruce Stands (2015)
    MDPI Publishing
    In: Forests
    Details
    Publication Date: 2015-12-16
    Description: We analyzed productivity, in terms of periodic annual increment (PAI) in volume, of pure and mixed unmanaged naturally regenerated boreal stands mainly comprised of Populus tremuloides Michx. (trembling aspen) and Picea glauca (Moench) Voss (white spruce) ranging from 25–260 years old, in Alberta, Canada. Measures of density, site occupancy (Reineke’s stand density index-SDI), height, and site quality were evaluated in non-linear regression models aiming to explain the variation in PAI for the separate component species and for the entire stand. Analyses also included examination of the influence of stand composition. Results indicated a positive effect of both density of deciduous trees and of the percentage of deciduous tree stand basal area on trembling aspen volume PAI. White spruce PAI was positively influenced by spruce and aspen basal area, although effects of aspen were small. Height of both aspen and spruce were the most consistent independent variables in the models tested. Maximum PAI was achieved in mixed stands when site occupancy of both species was at its maximum, indicating the ecological combining ability of these two species. Variation in maximum stocking densities (i.e., stockability) has a strong influence on increment in these forests and is a major factor leading to increased productivity of mixed compared to pure stands.
    Electronic ISSN: 1999-4907
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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