AVS 45th International Symposium
    Surface Science Division Thursday Sessions
       Session SS2-ThM

Paper SS2-ThM10
Reduction of Trace Element Contaminants in Aqueous Solution by Iron and Iron Oxides

Thursday, November 5, 1998, 11:20 am, Room 309

Session: Oxide Surface Chemistry
Presenter: S.R. Qiu, University of California, Riverside
Authors: S.R. Qiu, University of California, Riverside
H.-F. Lai, University of California, Riverside
J.A. Yarmoff, University of California, Riverside
C. Amrhein, University of California, Riverside
M.J. Roberson, University of California, Riverside
M. Hunt, University of California, Riverside
Correspondent: Click to Email
Irrigation drainage and wastewater often contain elevated levels of trace oxyanions and oxycations, such as selenate, chromate and uranyl, which can be detrimental to humans and wildlife. A potential remediation method is to reduce the contaminants to less mobile forms by reacting the water with zero-valent iron. In this reaction, the iron serves as both an electron source and a catalyst. Most previous studies of this system were limited to the simulation of field work on a macroscopic scale. Consequently, little is known about the basic chemical interactions of these toxic ions at the water-metal interface. Our objective is to determine the microscopic reaction mechanisms by combining surface science methods and bulk chemical studies. Our bulk studies have indicated that the reactions are first-order. For surface studies, iron foil is first prepared in a UHV chamber by sputtering, or iron oxides are prepared by exposure of a hot Fe foil to O2 in UHV. The sample is then transferred to an aqueous solution containing the relevant ions. The pH and amount of dissolved oxygen in the solution are carefully controlled. The reacted surfaces are then characterized in UHV by surface analysis techniques such as x-ray photoelectron spectroscopy (XPS) or scanning tunneling microscopy (STM). We find that films of partially reduced Se, Cr and U are formed by the reaction. The reduction of U is very sensitive to dissolved oxygen, while the reductions of Se and Cr are not. The details of the surface reduction reaction mechanisms will be presented, and the implications of our results on the practical deployment of this remediation method will be discussed.