The Role of Surface Complexes on Metal Incorporation into Minerals

Suny At Stony Brook, Stony Brook NY

Investigators

Abstract

Reeder EAR-0207756 This research project will investigate the fundamental structural and coordinative aspects of metal sorption at the calcite-water interface. The experimental approach will combine laboratory experiments in model systems with spectroscopic techniques to characterize the detailed coordination geometry of selected metal and metalloid species adsorbed on calcite. Metals of interest include divalent lead and cadmium, selected trivalent rare-earth elements, and arsenate anions. These species are important contaminants in soils, sediments, aquifers, and other near-surface environments. One goal of the research is to determine the role of adsorption in controlling binding site preferences for minor element uptake by calcite during crystal growth. Observations that non-octahedral surface complexes for Zn(II) and Cu(II) adsorbed on calcite result in preferential uptake on the less constrained of two binding sites, suggests that site preferences for other metals should also correlate with surface complex geometry. The proposed research tests this hypothesis for selected metals (Pb and Cd) and provides structural information that can be used in predictive models. A further goal of the research is to evaluate how adsorption complexes control the coordination of rare-earth elements following incorporation into calcite, where observations have shown differences in coordination number between light and heavy lanthanides. The role of solution pH on the structure of surface complexes will also be evaluated in laboratory and spectroscopic studies. Another component of the research project will identify the mechanism of adsorption of arsenate ions on calcite. Arsenate, an important contaminant in some natural waters, shows similarities in behavior with phosphate. The latter is a strong inhibitor of calcite surface reactivity, and its presence may reduce the ability of calcite to sorb and incorporate other impurity species. The results of this aspect of the research will provide insight to the mechanism of surface inhibition as well as provide fundamental information about arsenate interactions with calcite. Results from this research project will contribute to a broader understanding of the molecular-scale processes that govern the distribution and behavior of geochemically and environmentally important elements in Earth's near-surface environment. The results of this work will also contribute to an understanding of ways in which the threat to society posed by metal contaminants can be reduced.