COUPLED IRON CORROSION AND CHROMATE REDUCTION - MECHANISMS FOR SUBSURFACE REMEDIATION

The reduction of chromium from the Cr(VI) to the Cr(III) state by the presence of elemental, or zero-oxidation-state, iron metal was studied to evaluate the feasibility of such a process for subsurface chromate remediation. Reactions were studied in systems of natural aquifer materials with varying geochemistry. Different forms of iron metal had significantly different abilities to reduce chromate, ranging from extremely rapid to essentially no effect. Impure, partially oxidized iron was most effective, with iron quantity being the most important rate factor, followed by aquifer material type and solid:solution ratio. Evidence for chromium-iron hydroxide solid solution (CrXFe1-x)(OH)(3)(ss) formation was obtained by electron probe microanalysis. A cyclic, multiple reaction electrochemical corrosion mechanism, enhanced by the development of an electrical double-layer analogue, is proposed to explain the differing iron reactivities and aquifer material effects.