Iron Sulfide-arsenite Interactions: Adsorption Behavior onto Iron Monosulfides and Controls on Arsenic Accumulation in Pyrite

Arsenic mobility in natural systems is often linked to iron and sulfur cycling at redox boundaries, apparently due to co-precipitation reactions of arsenic with poorly crystalline iron (oxy)hydroxides, iron monosulfides, and pyrite (e.g., Edenborn et al., 1986; Moore et al., 1988). The mobility of arsenic under anoxic, sulfate-reducing conditions is expected to be governed by interactions between arsenite or thioarsenite species with amorphous or crystalline iron sulfides. Iron sulfide minerals are especially common components of soil/sedimentary environments, and reactions at the surfaces of iron sulfides play pivotal roles in metal retention, mobility, and bioavailability (Huerta-Diaz and Morse, 1992). Although essential for predicting the fate of arsenic in anoxic environments, details of reaction mechanisms, geochemical pathways, and the limiting factors that govern metal uptake by iron sulfides (iron monosulfides and iron disulfides) are incompletely understood. The kinetic nature of these interactions are currently being investigated at EPA’s Subsurface Protection and Remediation Division where on-going studies evaluate the effects of pyrite nucleation rate and growth rate on the uptake of metals and metalloids.