CATION-TRANSPORT IN NATURAL POROUS-MEDIA ON LABORATORY-SCALE - MULTICOMPONENT EFFECTS

Multicomponent transport experiments were performed with four major cations, Na+, K+, Ca2+ and Mg2+, in laboratory columns packed with a non-calcareous soil. The breakthrough curves are explained quantitatively with a box model including cation exchange. We use a single set of selectivity coefficients, an independently verified value of the cation-exchange capacity (CEC), and an adjusted value of the Peclet number. This Peclet number is smaller than the value determined from independent tracer experiments. The model is able to predict all experimentally observed breakthrough curves quite well. The selectivity coefficients determined from binary exchange experiments prove unreliable for the prediction of multicomponent experiments. We propose to estimate the selectivity coefficients by directly fitting the multicomponent breakthrough curves. Their shape is a very sensitive function of the values of these coefficients. Concepts from non-linear chromatography can be used in order to interpret several qualitative features of the breakthrough curves.