The incorporation of impurities in minerals has far-reaching implications for large-scale issues as varied as the fate and transport of anthropogenic contaminants in terrestrial and subsurface ecosystems, the composition of seawaters and sedimentary pore waters, and environmental remediation technologies. Yet, our understanding of the fundamental mechanisms that control impurity incorporation in minerals remains poor. For example, the charge compensation schemes that allow for aliovalent substitution are rarely known. This knowledge gap represents a clear impediment to the development of predictive models of tracer and contaminant incorporation. Extended X-ray absorption fine structure spectroscopy (EXAFS) would be ideally suited to determine the local, atomic-level structure around impurities in minerals, however, interpretation of EXAFS data is remarkedly challenging due to the high degree of static disorder usually associated with impurity incorporation. A solution is to use spectra calculated from atomic trajectories generated by ab initio molecular dynamics (AIMD) simulations as standards in linear combination fits to measured spectra. In this presentation, we will review several success stories in which this AIMD-EXAFS approach was used to resolve the nature, proportion, and structure of the multiple coordination environments around first-row transition metals, rare-earth elements, actinides, and oxyanions incorporated in calcite (CaCO<sub>3</sub>). Calcite can incorporate many types of impurities and is abundant in sediments and sedimentary rocks. Implications for the bioavailability of toxic metals, the immobilization of contaminants, and the use of rare-earth elements as biogeochemical tracers will be discussed.

Fundamental mechanisms of tracer and contaminant incorporation in minerals

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.