Electrical Conductivity Breakthrough Curves

The factors affecting the applicability of electrical conductivity ( EC ) breakthrough curves as an indicator of chemical equilibrium between effluent and influent solutions in compatibility tests are illustrated. The shapes of EC breakthrough curves are shown to be a function of the flow rate, the solute retardation factor, the species of cation and anion in the permeant liquid, and the cation initially occupying the exchange complex of the clay. Measured data show that the magnitude of the EC in the soil due to the existence of soluble salts relative to the EC of the influent solution (permeant liquid) affects significantly the observed shapes of the EC breakthrough curves. Comparison between theoretically predicted and measured EC breakthrough curves varies from good to excellent, depending on the initial conditions for the test. The results indicate that chemical equilibrium can not be attained before complete EC breakthrough is attained, regardless of the shape of the EC breakthrough curve. Thus, EC breakthrough curves offer a potentially simple, practical, and inexpensive method for determining chemical equilibrium in laboratory compatibility tests involving permeation with electrolyte solutions.