ALBERT

Description:    Membrane behavior in naturally occurring and engineering systems refers to the restriction of solute migration through a membrane relative to the migration of the solvent. Hyperfiltration is the net flux that results when two solutions of different concentration are separated by a membrane and an external force is applied in excess of the osmotic pressure. Clay membranes containing layered fabric have higher efficiencies than membranes with random fabrics. Therefore, low-permeability rocks with a foliated fabric might exhibit membrane properties. Four hyperfiltration experiments were conducted on samples of Darrington Phyllite from the Easton Metamorphic Suite of the Northwest Cascades, Washington (USA). Chloride solutions were passed through thin, intact discs at relatively low heads. At the end of the experiments, dissolved chloride concentrations had increased 110–140 % and calculated reflection coefficients ranged from 0.87 to 0.88; this was attributed to partial solute rejection by the phyllite. Natural scenarios in which phyllite might exhibit membrane properties include (1) shallow perched aquifers bounded by phyllite, (2) overpressured aquifers bounded by phyllite, (3) phyllite-bounded aquifers with significant vertical groundwater flows, and (4) ultrafiltration during metamorphic devolatilization at depth. Membrane processes exhibited by phyllite may also contribute to the formation of some low-temperature ore bodies. Content Type Journal Article Category Report Pages 1-9 DOI 10.1007/s10040-012-0905-8 Authors Megan Hart, Department of Civil Engineering, Saint Louis University, 3450 Lindell Blvd., Room 1033, Saint Louis, MO 63103, USA Journal Hydrogeology Journal Online ISSN 1435-0157 Print ISSN 1431-2174