Removal of contaminated Zn from consolidated soil by electrokinetic method employing ion-exchange reaction

An electrokinetic method employing an ion-exchange reaction has been developed for remediation of soils contaminated with heavy metals, having relatively low hydraulic permeability. Consolidated bentonite cake contaminated with zinc was prepared by the mechanical expression method, and the removal of zinc ions from the cake was examined by the electrokinetic method employing the addition of sodium ions. From the preliminary adsorption test of zinc ions onto bentonite clay, the adsorption behavior was found to be described by an equation of the Freundlich type. Zinc ions were desorbed from the bentonite due to a cation-exchange reaction caused by the addition of sodium ions, and were efficiently removed from a cake of low hydraulic permeability by electroosmotic flow. The permeation rate of the liquid through the cake at the steady state was found to increase linearly with the current density, and the rejection ratio of the zinc ion was independent of the current density. Consequently, it appeared that the rejection rate of the zinc ion was proportional to the current density. Moreover, at the steady state, the variation of the rejection ratio with the permeate volume became marked with the increase of the concentration of added zinc ions, and it was not influenced by the cake thickness.