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 permeable reactive barrier material to mitigate the transport of a wide array of highly mobile contaminants in groundwater. Zero-valent iron has previously been shown to destroy effectively numerous chlorinated hydrocarbon 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 determine the capability of particulate Fe-0 to remove UO22+, MoO42-, TcO4-, and CrO42- from groundwater. Particulate Fe-0 effectively removed each of these contaminants from solution; removal rates decreased as follows: CrO42- > TcO4- > UO22+>>MoO22-. The removal mechanism appears to be reductive precipitation. Thermodynamic equilibrium calculations indicated that the rate of removal of the metals from solution increased as the difference in pe (Delta pe) increased between the redox half reaction for the redox couple of interest and the Fe-0/Fe2+ couple. Furthermore, the pe value for a redox couple provided a qualitative indication of the reduction rate by Fe-0. These results indicate that the rate of removal of CrO42-, TcO4-, and UO22+ from groundwater is rapid, permitting an inexpensive barrier of practical dimensions to be used for in situ remediation purposes.