ZERO-VALENT IRON FOR THE IN-SITU REMEDIATION OF SELECTED METALS IN GROUNDWATER

Zero-valent iron (Fe-0), metallic iron, is being evaluated as a permea ble reactive barrier material to mitigate the transport of a wide arra y of highly mobile contaminants in groundwater. Zero-valent iron has p reviously been shown to destroy effectively numerous chlorinated hydro carbon compounds via reductive dehalogenation. No references could be found regarding the ability of zero-valent iron to reduce UO22+, MoO42 -, or TcO4-. A series of kinetic-batch studies was conducted to determ ine the capability of particulate Fe-0 to remove UO22+, MoO42-, TcO4-, and CrO42- from groundwater. Particulate Fe-0 effectively removed eac h of these contaminants from solution; removal rates decreased as foll ows: CrO42- > TcO4- > UO22+>>MoO22-. The removal mechanism appears to be reductive precipitation. Thermodynamic equilibrium calculations ind icated that the rate of removal of the metals from solution increased as the difference in pe (Delta pe) increased between the redox half re action for the redox couple of interest and the Fe-0/Fe2+ couple. Furt hermore, the pe value for a redox couple provided a qualitative indica tion of the reduction rate by Fe-0. These results indicate that the ra te of removal of CrO42-, TcO4-, and UO22+ from groundwater is rapid, p ermitting an inexpensive barrier of practical dimensions to be used fo r in situ remediation purposes.