Miscible Displacement: V. Exchange Processes
1963
Biggar, J. W. | Nielsen, D. R.
Miscible displacement experiments have shown that the physical processes associated with microscopic flow velocities should be included in any theory of exchange during flow through soils. Water contents and average-flow velocities were controlled in Oakely soil columns initially saturated with Ca ion. Without disturbing the water content and flow velocity, Ca acetate of 0.1N and 0.05N concentration was displaced by MgCl₂ solutions of similar concentration. The distribution of Mg²⁺ and Cl⁻ ion in the effluent was related to the volume passing through. Mg²⁺ ion appeared in the effluent well in advance of that predicted on the basis of exchange theory. Three mathematical models that include the exchange process were compared with the data to ascertain their usefulness in predicting positions and shapes of breakthrough curves. Although the theories were generally inadequate, they did serve to emphasize the important contribution of microscopic flow velocity and ionic diffusion to the mixing or dispersion of solutions in porous media and to exchange processes.
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