A Comparison of Sorption Equilibrium Distribution Coefficients Using Batch and Centrifugation Methods

Abstract

AbstractSorption equilibrium distribution coefficients, Kd's, are often used in solute transport models to predict the movement of hazardous wastes in soils. Kd values can be determined in the laboratory by performing batch equilibrium tests or column studies. However, these tests suffer from disadvantages. Batch tests may overestimate sorption in natural soils due to the solids effect, and column studies conducted with fine‐grained soils require a long time to conduct. Centrifugation testing can alleviate these disadvantages by testing a soil column instead of a soil suspension, by imposing a confining stress on the soil, and by producing a greater pore water velocity. Centrifuge experiments were conducted on a kaolinite/phenol system using a constant head permeameter and a laboratory centrifuge. Kd values were estimated by modeling the generated breakthrough curves with a solute transport model. Kd values obtained in the centrifuge experiments were compared with Kd values measured in batch equilibrium tests. Although the Kd values determined in the centrifuge were slightly lower than the values predicted by extrapolating the batch data, the results were consistent with the solids effect.