Abstract: Experimental evidence of the salt filtering ability of compacted bentonite and clay material is presented. Apparatus has been developed in which samples of semi-dry powdered bentonite and shale are compacted under pressures of 10,000 psi and subjected to flow with sodium chloride solutions under fluid pressures up to 10,000 psi. Porosities of 34–41 percent have been obtained with the bentonite and 24 percent with the shale. Permeabilities of 10−5 to 10−6 millidarcies have been measured. A ratio of input to output solution concentration as high as 8 has been found with the bentonite samples and dilute (0.164 N) NaCl solutions. The ratio falls off with increased input concentration and with increased porosity. The shale sample has given a ratio of 1.7 with an input concentration of 0.129 N NaCl.
Streaming potential differentials of approximately 1 mV per 100 psi have been measured during the flow experiments. The potential differential is highest with the shale material and shows a decrease with increasing salt concentration.