Molecular-Level Processes Governing the Interaction of Contaminants with Iron and Manganese Oxides

The central tenet of this program is that a fundamental understanding of specific mineral surface-site reactivities will substantially improve reactive transport models of contaminants in geologic systems, and will allow more effective remediation schemes to be devised. To this end, we are carrying out a program of research that focuses on the fundamental mechanisms of redox chemistry of contaminants on mineral surfaces. As much of this chemistry in sediments involves the iron(III)/iron(II) couples, we are focusing on mineral phases containing these species. Our approach is to conduct carefully controlled experiments on model, single-crystal iron oxide mineral surfaces grown by molecular beam epitaxy, natural iron oxide single crystals, and synthetic mineral powders. We use the results from the model surfaces, which are very well defined in terms of surface composition, structure, and defect densities, to understand the results obtained on more complex mineral specimens. We ar e using a variety of experimental probes, along with molecular modeling theory, to determine clean mineral surface structure, details of the chemisorption and decomposition of water, and the interface structure and redox chemistry of important contaminants such as CrO4 -2 on these surfaces