ELECTRORESTORATION OF METAL-CONTAMINATED SOILS

The removal of metals from contaminated soils using electric fields ha s been successfully demonstrated in the laboratory, yet field trials h ave yielded anomalous results. Poor performance may be attributed to i nteraction of the metals with naturally occurring electrolytes, humic substances, and co-disposed wastes. Immobilization of contaminants in a narrow band in the soil, analogous to isoelectric focusing, was repr oduced experimentally and simulated with a mathematical model. It was shown that the focusing effect can be eliminated by controlling the pH at the cathode using a water rinse. Immobilization resulting from pre cipitation with carbonates and co-disposed wastes may additionally req uire chelating agents and control of the redox potential to effect rem oval. Pourbaix diagrams provide a means for rapidly identifying pH and redox conditions suitable for mobilizing metal wastes. Optimum operat ing conditions can then be determined using a mathematical model that incorporates the appropriate metal speciation chemistry.