The Flow of Salt Solutions Through Compacted Clay

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 wlth 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. PermeablUties of 10-s to 10-e 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) NaC1 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 NaC1. 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.

Coupling Effects during Steady-State Solute Diffusion through a Semipermeable Clay Membrane

“…The second term in eq 3 represents the explicit diffusive coupling term that arises due to the soil membrane behavior. This explicit diffusive coupling term has been called salt sieving (30,31), hyperfiltration (32), or streaming current (13). If the soil exhibits no membrane behavior, then ω ) 0 and eqs 2 reduce to the traditional form for Fick's first law for diffusion in soil (27).…”

Experimental device for chemical osmosis measurement on natural clay-rock samples maintained at in situ conditions: Implications for formation pressure interpretations

“…The coupled fluxes are due to some additional driving forces such as the chemical potential of the fluid for instance. Coupled flow processes were clearly evidenced in compacted clay rocks [1][2][3][4][5][6]. When they occur, the classical Darcy's law is no longer sufficient and a generalized version of this law must be used.…”

Clay Diagenesis in the Barbados Accretionary Complex: Potential Impact on Hydrology and Subduction Dynamics

“…Clays such as smectite, with high net surface charges and high cation ex change capacities, make the best geologic membranes (Fritz, 1986). Experimental work on the efficiency of clay minerals as geologic membranes has shown that filtration efficiency varies with cation size and charge, compaction pressure, flow rate, and temperature (e.g., McKelvey and Milne, 1962;Hanshaw and Coplen, 1973;Kharaka and Smalley, 1976). Filtration ratios (ratio of input to output concentration of an ion) for solutions passing through bentonite (altered volcanic ash containing a high proportion of smectite) are generally in the range of 1 to 8 Figure 7.…”