JOURNAL OF Contaminant Hydrology ELSEVIER Journal of Contaminant Hydrology 16 (1994) 319- 337 Cation transport in natural porous media on laboratory scale: multicomponent effects Miroslav Cernik, Kurt Barmettler, Daniel Grolimund, Werner Rohr, Michal Borkovec*, Hans Sticher Institute of Terrestrial Ecology, Federal Institute of Technology ( ETH), Grabenstrasse 3. CH-8952 Schlieren, Switzerland (Received December 6, 1993; revision accepted April 27, 1994) Abstract Multicomponent transport experiments were performed with four major cations, Na +, K +, Ca 2+ and Mg 2+, 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 coeffÉcients, an independently verified value of the cation-exchange capacity (CEC), and an adjusted value of the P6clet number. This P6clet 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 multi- component 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. 1. Introduction Modeling reactive transport in porous media has become an increasingly important tool for quantitative predictions of pollutant fate in soils, aquifers and fractured rocks. In recent years much progress was made in the description of transport of conservative tracers on the laboratory and field scale. Such solutes which adsorb very weakly on the solid matrix (e.g., chloride, nitrate) are transported by pore-water flow. Over a limited spatial and temporal scale the transport of such conservative tracers can be often modeled with the convection-dispersion equation (Dagan, '989). Most * Corresponding author. 0169-7722/94/$07.00 © 1994 - Elsevier Science B.V. All rights reserved SSDI 0169-7722(94)0000-0