Hyperfiltration of Nacl Solutions Using a Simulated Clay/Sand Mixture at Low Compaction Pressures

Abstract

It is widely recognized that clays and shales can demonstrate membrane properties. When a hydraulic head differential exists across a membrane-functioning clay-rich barrier, some of the solute is rejected by the membrane. This process is known as hyperfiltration. Some shallow geologic environments, including aquitards bounding shallow perched aquifers and unconfined aquifers, some river and stream beds, and some lake bottoms contain clay-soil mixes. Many engineering structures such as landfill liners, mixed soil augered barriers, and retention pond liners also consist of soil-clay mixes. No previous testing has been performed to investigate the likelihood that hyperfiltration may occur in such mixed soils. Therefore, we performed five experiments using different mixes of Na-bentonite and glass beads (100, 50, 25, 12 and 0% clay) to determine if any of these mixes exhibited membrane properties and to investigate what effect clay content had upon the membrane properties of the soil. Each mixture was compacted to 345 kPa and the sample mixtures were 0.58-0.97 mm thick. All the experiments used an approximately 35 ppm Cl ) solution under an average 103 kPa hydraulic head. Experimental results show that all the simulated clay-sand mixtures do exhibit measurable membrane properties under these conditions. Values of the calculated reflection coefficient ranged from a low of 0.03 for 12% bentonite to 0.19 for 100% bentonite. Solute rejection ranged from 5.2% for 12% clay to a high of over 30% for the 100% clay. The 100% glass bead sample exhibited no membrane properties.

Membrane behavior of compacted sand–bentonite mixture

“…Although the results of this study likely represent the first evaluation of a SB mixture for membrane behavior, the study did not include any assessment of the potential effect of compaction on the measured hydraulic conductivity, such as those commonly employed to evaluate the suitability of a material for use as a compacted clay barrier (e.g., Daniel and Benson 1990;Benson et al 1999). Saindon and Whitworth (2005) used hyperfiltration tests to measure the reflection coefficients (membrane efficiencies), , of mixtures of glass beads and bentonite containing 12%, 25%, and 50% Wyoming Na-bentonite. The mixtures were considered to simulate SB mixtures, with the glass beads representing sand.…”

Critical review of coupled flux formulations for clay membranes based on nonequilibrium thermodynamics

“…In addition, recent experimental studies have indicated the existence of membrane behavior in engineered clay barriers used for hydraulic containment applications (e.g., landfills, surface impoundments, etc. ), such as geosynthetic clay liners (GCLs), compacted clay liners, and soil-bentonite backfills for vertical cutoff walls (Di Emidio, 2010;Evans et al, 2008;Henning, 2004;Henning et al, 2006;Kang, 2008;Kang and Shackelford, 2009, 2010, 2011Malusis, 2001;Malusis andShackelford, 2002a,2002b;Malusis et al, 2001;Mazzieri et al, 2003Mazzieri et al, , 2005Mazzieri et al, , 2010Saindon and Whitworth, 2005;Shackelford, 2012;Shackelford and Lee, 2003;Van Impe, 2002;Yeo, 2003;Yeo et al, 2005). Collectively, this extensive body of research has demonstrated that significant membrane behavior is possible in clay soils, particularly those soils rich in high swelling smectite minerals, such as bentonite (Di Emidio, 2010;Kang and Shackelford, 2010;Kemper and Quirk, 1972;Kemper and Rollins, 1966;Malusis and Shackelford, 2002a;Milne et al, 1964;Shackelford, 2012;Yeo et al, 2005).…”

Calibrating a model to 30 years of data to capture the accumulation of chloride from winter deicers in a shallow aquifer

“…In particular, the clay till deposits vary in thickness from 0 to 34 meters (Roadcap et al, 1993) across our study area and are likely to impact chloride travel time to the aquifer (Gahala, 2017). Clay layers can act as a natural filter and seal higher chloride concentrations on one side of the layer, an effect that increases with clay percentage (Saindon & Whitworth, 2005).…”