Isothermal Coupled Transport Processes in Soils and Clays

Coupled osmotic transport processes involving passage of aqueous electrolytes across bentonite clay membrane in Ca and K forms and four soils of contrasting properties have been studied. The experimental data have been fitted to formulations based on irrevers.ible thermodynamics to yield appropriate reflection coefficient (σ), mechanical filtration capacity of soil (L_p). and solute permeability (w) for various transport systems. The reflection coefficient (σ) for transport across clay membranes increased with rise in temperature, and showed decrease with increasing electrolyte concentration. For transport of aqueous electrolytes across soil plugs, a was lowest in the Jhargram soil and highest in the Chinsurah soil. The L_p was inversely proportional to clay content of the soils. Salt accumulation in soil profile has been discussed with the help of decoupling of solute and solvent during osmotic flow in terms of the relevant hydrodynamic frictional coefficients and related to the properties of the soils, especially the content and nature of the clay fraction present.