Environmental Geochemistry of Chromium and Selenium: Spectroscopy, Solution Chemistry, Electrochemistry, and Collaborative Field Studies

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9406490 Brown This project focuses on factors that control the geochemical behavior of Cr and Se in soils, sediments, and natural waters particularly those affecting their sorption on the surfaces of common oxide and clay minerals. It integrates laboratory studies of the surface geochemistry of magnetite, kaolinite, and smectite and the sorption and redox behavior of Se on these minerals and Cr on magnetite with several ongoing field investigations of the environmental geochemistry of Cr and Se in magnetite- and clay-bearing sediments being conducted by associate investigators from the USGS and LBL. The objectives of this proposed research are (1) to define quantitatively reaction stoichiometries and the geometry and composition of Cr(III) and Cr(VI) complexes sorbed on magnetite and of Se(IV) and Se(VI) complexes sorbed on magnetite, kaolinite, and smectite; (2) to characterize the magnetite surface before and after sorption using various spectroscopic and scattering techniques; (3) to utilize the results of our spectroscopic measurements in developing a predictive macroscopic model of sorption behavior and fluid-solid partitioning of chromium and selenium ions; and (4) to study the speciation of chromium and selenium in natural sediments and soils from two field sites. The proposed research builds on NSF-funded studies of sorption processes of inorganic solutes at mineral-water interfaces of the past six years and is a natural extension to systems involving redox-sensitive inorganic solutes.