Electrolyte-induced solute permeability effects in compacted smectite membranes |
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| Institution: | 1. Department of Earth, Environment and Life Sciences, University of Genoa, C.so Europa 26, IT-16132 Genoa, Italy;2. Department of Earth Sciences, University of Zaragoza, Pedro Cerbuna 12, ES-50009 Zaragoza, Spain;1. Department of Geoscience, University of Wisconsin, Madison, WI 53706, United States;2. Department of Civil and Environmental Engineering, University of Iowa, Iowa City, IA 52242, United States;3. Pacific Northwest National Laboratory, Richland, WA 99352, United States;1. Division of Ocean Science and Technology, Graduate School at Shenzhen, Tsinghua University, Shenzhen, 518055, China;2. School of Environment, Tsinghua University, Beijing, 100084, China;1. College of Materials Science and Engineering, Fuzhou University, Fujian 350116, China;2. School of Mechanical Engineering and Automation, Fuzhou University, Fujian 350116, China;3. Instrumentation Analysis and Measurement Center, Fuzhou University, Fujian 350116, China;1. Department of Civil Environmental and Architectural Engineering University of Colorado, Boulder, United States;2. Department of Civil Environmental and Geo‐ Engineering University of Minnesota, Twin Cities, United States |
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| Abstract: | Experiments suggest that increasing electrolyte flux into a compacted smectite membrane may result in greater permeability of the membrane to the electrolyte. The influx of electrolyte into the membrane pores decreases the double layer thickness, therefore reducing the clay's ability to exclude anions. As a result, solute previously accumulated in the concentration polarization layer (CPL) may be able to dissipate through the membrane, producing a temporary situation where the effluent is more concentrated than the feed solution. Of course, at some juncture the CPL will diminish sufficiently so that the effluent concentration will be the same as that of the feed solution and a true state will be reached.The fact that increasing electrolyte concentration within the clay membrane decreases the membrane efficiency implies that the result of solute accumulation in geological basins, even though a portion of such accumulation is attributable to the solute filtering ability of low permeability rocks, is the ultimate cessation of membrane effects. At the start of the cycle, shale membranes have low solute concentrations and thus high rejection capabilities. The largest amount of solute accumulates deep in the basin center, where vertical flux rates are high. Because of greater solute concentration within the aquifer, the solute concentration in the centrally located membranes rises more quickly than that of those located near the basin margins. Therefore, the cessation of membrane effects occurs first in the deep center of the basin and gradually moves upward and outward toward the basin margins. The fact that membrane efficiency decreases as pore solute concentration increases might help explain why conclusive trends attributable to membrane effects have not been more commonly observed in the subsurface. |
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