Applicability of the Local Equilibrium Assumption to Transport through Soils of Solutes Affected by Ion Exchange

作者：Ronald V. James, Jacob A. Rubin · 发表于：ACS symposium series · 年份：1979 · DOI：10.1021/bk-1979-0093.ch011 · 被引用次数：60 · 研究领域：Soil and Unsaturated Flow、Groundwater flow and contamination studies、Electrokinetic Soil Remediation Techniques

Abstract Miscible displacement of calcium-chloride solutions through water-saturated laboratory soil columns was studied for a wide range of constant water-flow rates. Calcium- and chloride-effluent histories were obtained. Calcium self-exchange was the only reaction considered. Calcium-effluent histories were compared with predictions from a one-dimensional solute-transport model, assuming local chemical equilibrium. Good agreement between the predictions and the data was obtained for the slowest flow rate studied, but not for the higher fluxes. Thus, the local equilibrium assumption applies when the ratio of the hydrodynamic dispersion coefficient to the estimated molecular-diffusion coefficient is near unity. This conclusion is further substantiated by comparison with the results of a theoretical analysis using the relatively simple transport model for solutes affected by ion exchange that has been developed by Glueckauf ( 19 ). It is suggested that the data obtained for the higher water fluxes that yield a coefficient ratio much greater than unity cannot be described by assuming local equilibrium, but must be modeled using another relationship, presumably one involving kinetics.