Hyperfiltration of Nacl Solutions Using a Simulated Clay/Sand Mixture at Low Compaction Pressures |
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Authors: | Rosanna?Saindon Email author" target="_blank">T?M?WhitworthEmail author |
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Institution: | (1) Department of Geological and Petroleum Engineering, University of Missouri-Rolla, Rolla, MO, 65409 |
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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. |
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Keywords: | clay bentonite hyperfiltration reverse osmosis engineered barriers aquitard |
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