THEORETICAL MODELING OF MIXED-ELECTROLYTE SOLUTION FLOWS FOR UNSATURATED SOILS

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Abstract
A mixed salt solution with ions that interact with the soil matrix are important in field problems involving the simultaneous flow of water and mixed Na-Ca salts in unsaturated soils. Governing partial differential equations describing transient, one-dimensional, simultaneous transfer of mixed anions, cations, and water are formulated, taking into account physicochemical interaction between mono and divalent ions and the soil matrix. Effects of convection, diffusion, mechanical dispersion, anion exclusion, cation exchange and adsorption, and coupling phenomena are considered jointly. Soil-interacting and coupling parameters are estimated theoretically from mixed-ion diffuse double-layer theory, taking into account tactoids, capillarity, and hydrodynamic considerations. The coupling-interacting parameters include: osmotic efficiency coefficient, anion exclusion, cation exchange equilibria, soil water retentivity, and unsaturated hydraulic conductivity and their dependence on soil water content and soil solution concentration and composition. A finite difference approach that eliminates numerical dispersion is used to approximate the nonlinear partial differential equations and the boundary conditions appropriate to infiltration, redistribution, drainage, and evaporation of soil water. A brief computational scheme concludes the paper. A mixed salt solution with ions that interact with the soil matrix are important in field problems involving the simultaneous flow of water and mixed Na-Ca salts in unsaturated soils. Governing partial differential equations describing transient, one-dimensional, simultaneous transfer of mixed anions, cations, and water are formulated, taking into account physicochemical interaction between mono and divalent ions and the soil matrix. Effects of convection, diffusion, mechanical dispersion, anion exclusion, cation exchange and adsorption, and coupling phenomena are considered jointly. Soil-interacting and coupling parameters are estimated theoretically from mixed-ion diffuse double-layer theory, taking into account tactoids, capillarity, and hydrodynamic considerations. The coupling-interacting parameters include: osmotic efficiency coefficient, anion exclusion, cation exchange equilibria, soil water retentivity, and unsaturated hydraulic conductivity and their dependence on soil water content and soil solution concentration and composition. A finite difference approach that eliminates numerical dispersion is used to approximate the nonlinear partial differential equations and the boundary conditions appropriate to infiltration, redistribution, drainage, and evaporation of soil water. A brief computational scheme concludes the paper. © Williams & Wilkins 1978. All Rights Reserved.

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