ON THE KINETICS OF CHARGED CONTAMINANT REMOVAL FROM SOILS USING ELECTRIC-FIELDS

A basic model is presented for the electric-held-driven removal of tox ic ionic species from a porous medium followed by the replacement of t he toxic species by nontoxic species having the same charge, The model takes into account only the principal mechanism of contaminant transp ort which, in the case of a charged contaminant, is electromigration. In the diffusionless approximation, the process of contaminant removal is described by a set of quasilinear hyperbolic equations which are s imilar to those arising in gas dynamics, chromatography, and electroph oresis. Analysis of these equations is carried out for the simple case of a ternary system consisting of two replacing cations and one anion . Depending on the relative mobilities of the toxic and nontoxic speci es, the medium is shown to be subdivided into either two or three movi ng zones with qualitatively different distributions of the species. Th e velocities of the zone boundaries and the time for complete removal of the contaminant from the medium are calculated analytically and int erpreted physically for both constant electric current and constant po tential difference across the porous medium, Theoretical predictions f rom the model are tested by comparing the calculated and experimentall y measured conductivities of the medium, which vary with time in the c ourse of the replacement of the toxic species by the nontoxic species of different mobilities. Conclusions regarding the process performance and efficiency are derived from the results. (C) 1996 Academic Press, Inc.