(155a) The Kinetics of Redox Reactions of Hexavalent Chromium and Trichloroethylene In Wastes Containing Both Contaminants

This paper presents the feasibility of using oxidizing and reducing agents for the simultaneous remediation of heavy metals and chlorinated hydrocarbons in aqueous and soil systems. Chelsea soil was selected as a model soil while trichloroethylene (TCE) and hexavalent chromium (Cr(VI)) were selected as model contaminants. Ferrous ion, Fe(II) was used as a reducing agent while permanganate, (MnO₄^-), was used as an oxidizing agent. Bench-scale experiments were conducted to determine the reaction kinetics and extent of redox reactions of Cr(VI) and TCE in separate and combined systems in both aqueous and soil systems. In the redox reaction, Cr(VI) is reduced to the nonhazardous Cr(III), and Fe(II) is oxidized to ferric ion, Fe(III); while TCE is oxidized to chloride, hydrogen, and carbon dioxide and permanganate is reduced to manganese dioxide (MnO₂.). In the experimental analysis, the Cr(VI)-Fe(II) reaction yielded 100%  and 99% Cr(VI) reduction when Fe(II) was used in water and Chelsea soil, respectively. The overall reaction was determined to be second order, first order with respect to both Cr(VI) and Fe(II). The TCE-KMnO₄ reaction yielded 100%, and 82% TCE oxidation by excess MnO₄^-  in water and Chelsea soil, respectively. The overall reaction was determined to be second order reaction, first order with respect to both TCE and MnO₄^- in both the aqueous and soil systems. The Cr(VI)-TCE reaction yielded 92% Cr(VI) reduction in water when excess TCE was used in the absence of Fe(II) and KMnO₄. The overall reaction was determined to be second-order overall, first order with respect to both Cr(VI) and TCE. TCE was found to have a significant effect on the reduction of Cr(VI) and vice versa.  When TCE was present in the aqueous system, the Cr(VI)-Fe(II) reaction with the same experimental conditions as before yielded 94% Cr(VI) reduction. Presence of TCE was advantageous to the reduction of Cr(VI), as it acted as an additional reductant.  When Cr(VI) was present in the aqueous system, TCE-KMnO4 reaction with the same conditions as before yielded 97% TCE oxidation.