Cation competition in a natural subsurface material: Prediction of transport behavior

Predicting the transport of reactive chemicals in subsurface porous media requires accurate adsorption models. This study compares the ability of various cation exchange models to quantitatively capture the transport behavior of major cations (i.e., calcium and sodium) in soil laboratory columns over a wide range of pore water composition. Experimental breakthrough curves were compared with model predictions without adjustable parameters. Various one‐site and multisite cation exchange models were independently calibrated with batch adsorption data. Our results show that a one‐site cation exchange model based on the well‐known Gaines‐Thomas convention yields good predictions of cation transport behavior, although some deviations from experimental data remain. The most reliable predictions were obtained with multisite cation exchange models with a distribution of various types of exchange sites.