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. 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 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. We have hypothesized that the phases most responsible for ANA reactivity are reactive mineral intermediates (RMI) that are derived from the more familiar and stable iron/sulfur minerals such as magnetite, pyrite, etc. Several lines of evidence for this hypothesis have been reported, mostly from batch experiments, but more recently from column and electrochemical experiments. The high rate and low capacity of RMI reaction with contaminants, co-contaminants, and other sources of natural reductant demand likely makes them dynamic and transient under many conditions, thereby contributing to some to the inconsistencies in prior work on ANA related processes.

<i>In situ</i> contaminant reduction by reactive mineral intermediate (RMI) phases

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In situ contaminant reduction by reactive mineral intermediate (RMI) phases