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

摘要

The mechanism for reclaiming sodic soils using calcium sulfate (CaSO_4) could provide a theoretical basis for the field application of CaSO_4 substitutes, including the by-products of flue gas desulfurization (BFGD), fly ash, and phosphorus gypsum. In this study, Ca~(2+) application experiment was conducted to analyze the dynamic changes of the cations in the reclamation of sodic soils with CaSO_4. 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 Ca~(2+) application experiment consisted of four treatments with four CaSO_ concentrations (0.5, 1, 1.5, and 2 g L~(-1)). When the Ca~(2+) concentrations in the supplied water were 14.71, 22.06, and 29.41 mmol L~(-1) Ca~(2+) achieved penetration, and this process was faster when the Ca~(2+) concentration in the supplied water was higher. Ca~(2+) did not achieve penetration when the Ca~(2+) concentration was 7.35 mmol L~(-1). UNSATCHEM was able to simulate the transportation mechanism of Ca~(2+) and Na~+ in the soil solution in the Ca~(2+) application experiment, the adsorption and exchange between the Na~+ in the soil colloid and Ca~(2+) in the soil solution, and the precipitation and dissolution of CaSO_4 with a high degree of accuracy. Sodic soil reclamation with CaSO_4 was not a short-term process. Compared with applying CaSO_4 only once, applying CaSO_4 in batches decreased the accumulation of soil salts and promoted its dissolution.