Many years of laboratory research on contaminant degradation by minerals has shown that freshly-formed (unaged) minerals generally are significantly more reactive than pre-formed (aged) minerals. However, the former are difficult to characterize and control, even in laboratory batch experiments, so the latter tend to dominate thinking about the role of mineral surfaces in contaminant fate and remediation. However, recent studies on the reactivity of pre-formed/aged minerals have shown that they may not be sufficient to explain the degree of contaminant degradation that is sometimes observed under (column or field) conditions that are favorable to abiotic natural attenuation (ANA). This inconsistency has led to renewed interest in the role of fresh-formed/unaged minerals in contaminant degradation under ANA conditions. It has been hypothesized that the phases most responsible for ANA reactivity are reactive mineral intermediates (RMIs) that are derived from the more familiar and stable iron/sulfur minerals such as magnetite, pyrite, etc. Evidence for the importance of RMI phases is mostly from laboratory studies, but these results have major implications for ANA, and in situ chemical reduction (ISCR) more generally. Several recent examples of this will be summarized, and new evidence will be presented from our most recent work using nitro aromatic compounds (NACs) as model contaminants. The latter was performed by titration of suspended iron oxides with Fe(II) and measuring NAC reduction, dissolved Fe(II), and pH. The results show that even NACs—which are among the most easily reduced environmental contaminants—react much more rapidly under conditions where RMIs are formed.

Reactive mineral phases from <i>in situ</i> biogeochemical processes: Key to abiotic natural attenuation?

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.

Reactive mineral phases from in situ biogeochemical processes: Key to abiotic natural attenuation?