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Mechanism and numerical simulation of multicomponent solute transport in sodic soils reclaimed by calcium sulfate

Wang, Jinman, Bai, Zhongke, Yang, Peiling
Environmental earth sciences 2014 v.72 no.1 pp. 157-169
adsorption, byproducts, calcium, calcium sulfate, cations, fly ash, gypsum, hydraulic conductivity, land restoration, mathematical models, phosphorus, reclaimed soils, sodic soils, sodium, soil salts, soil solution, solutes
The mechanism for reclaiming sodic soils using calcium sulfate (CaSO₄) could provide a theoretical basis for the field application of CaSO₄substitutes, including the by-products of flue gas desulfurization (BFGD), fly ash, and phosphorus gypsum. In this study, Ca²⁺application experiment was conducted to analyze the dynamic changes of the cations in the reclamation of sodic soils with CaSO₄. A multicomponent solute transport model (UNSATCHEM) that considers ion adsorption exchange and dynamic changes in the soil’s hydraulic conductivity was subsequently used to simulate and predict the movement of ions. The Ca²⁺application experiment consisted of four treatments with four CaSO₄concentrations (0.5, 1, 1.5, and 2 g L⁻¹). When the Ca²⁺concentrations in the supplied water were 14.71, 22.06, and 29.41 mmol L⁻¹, Ca²⁺achieved penetration, and this process was faster when the Ca²⁺concentration in the supplied water was higher. Ca²⁺did not achieve penetration when the Ca²⁺concentration was 7.35 mmol L⁻¹. UNSATCHEM was able to simulate the transportation mechanism of Ca²⁺and Na⁺in the soil solution in the Ca²⁺application experiment, the adsorption and exchange between the Na⁺in the soil colloid and Ca²⁺in the soil solution, and the precipitation and dissolution of CaSO₄with a high degree of accuracy. Sodic soil reclamation with CaSO₄was not a short-term process. Compared with applying CaSO₄only once, applying CaSO₄in batches decreased the accumulation of soil salts and promoted its dissolution.