Assessment of a predictive model to describe the migration of major inorganic cations in a Bt soil horizon

The aim of this study was to test the ability of a previous published model describing the sorption properties of complex solids (Bt soil horizon, sediment) under static conditions (batch mode) to describe sorption data obtained under dynamic conditions. This model assumes that the sorption properties of the multicomponent solid can be described by those of smectites present in the mineralogical assemblage. In our case, the reference smectite is a Wyoming montmorillonite. To test the model, experimental breakthrough curves of some major cations were obtained using a Bt soil horizon in different physico-chemical conditions. The fairly good agreement between the different experimental data sets and predicted breakthrough curves demonstrates that our proposed model can be used to accurately predict ion exchange reactions occurring under dynamic conditions between Na⁺, Ca²⁺, and H⁺ cations in a complex mineralogical assemblage. In addition, this model is also able to accurately predict previously published experimental data obtained with another B soil horizons and using Na⁺, Ca²⁺, and Mg²⁺ as cations. Other models reported from the literature, based either on sorption properties of pure smectites or of complex assemblages, are not able to accurately interpret experimental data proposed in this study motivating our purpose to propose another model. Therefore, our predicted model represents an alternative to models based on the generalized composite approach, which describes the reactivity of a complex material using generic sorption sites for which reactivity is not explicitly related to the properties of the individual phases of the complex material. (authors)