Groundwater arsenic (As) represents one of the most ubiquitous and challenging problems in environmental and public health.  We are still struggling to sufficiently understand the source of groundwater As, and to develop remediation strategies that can address it. Arsenic solid-soliution partition requires the concurrent characterization of organic carbon species, microbial community activity, and dissolved and solid-phase speciation of arsenic, iron and sulfur.  Here, we characterize the biology, chemistry and mineralogy of arsenic contamination, and use this information to optimize <i>in situ</i> magnetite precipitation to remediate As contamination. Results reveal unique coupling between iron reduction and the geochemical cycling of sulfur and carbon.  High As groundwater is uniquely associated with concurrent methanogenesis, Fe(III) and sulfate reduction in the presence of organic carbon. In many cases, these processes appear to be coupled to effective transport of intermediate organic carbon species that are rapidly transported from their origins.  One effective means of removing As from reducing groundwater is to produce magnetite, which stable and a strong As sorbent under most aquifer conditions. Here, we examine mechanisms of magnetite formation to establish how best to use this strong retention to solve As problems. Here we present research that demonstrates that nitrate dependent Fe(II) oxidation effectively produces nanoparticulate magnetite or green rust, a common magnetite precursor, under the most conditions.  Quantitative geochemical models of magnetite formation based on these results have been incorporated into the numerical code PHT3D to scale up these laboratory studies to field environments.<br/>

Characterizing and solving environmental arsenic contamination through combined geochemical, geobiological and organic matter characterization

255th National Meeting (2018)

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