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Performance of a Zerovalent Iron Reactive Barrier for the Treatment of Arsenic in Groundwater: Part 2. Geochemical Modeling and Solid Phase Studies
Citation:
BEAK, D. G. AND R. T. WILKIN. Performance of a Zerovalent Iron Reactive Barrier for the Treatment of Arsenic in Groundwater: Part 2. Geochemical Modeling and Solid Phase Studies. JOURNAL OF CONTAMINANT HYDROLOGY. Elsevier BV, AMSTERDAM, Netherlands, 106(1-2):15-28, (2009).
Impact/Purpose:
To evaluate arsenic uptake processes in a zerovalent iron reactive barrier installed at a lead smealting facility using geochemical modeling, solid-phase analysis, and X-ray absorption spectroscopy techniques.
Description:
Arsenic uptake processes were evaluated in a zerovalent iron reactive barrier installed at a lead smelting facility using geochemical modeling, solid-phase analysis, and X-ray absorption spectroscopy techniques. Aqueous speciation of arsenic plays a key role in directing arsenic uptake processes. Geochemical modeling reveals contrasting pH-dependencies for As(III) and As(V) precipitation. At the moderately alkaline pH conditions typically encountered in zerovalent iron reactive barriers, As(III) is unlikely to precipitate as an oxide or a sulfide phase. Conversely, increasing pH is expected to drive precipitation of metal arsenates including ferrous arsenate. Bacterially mediated sulfate reduction plays an important role in field installations of granular iron. Neoformed iron sulfides provide surfaces for adsorption of oxyanion and thioarsenic species of As(III) and As(V) and are expected to provide enhanced arsenic removal capacity. Arsenic removal in the PRB probably results from several pathways, including adsorption to iron oxide and iron sulfide surfaces, and possible precipitation of ferrous arsenate. As(0) was not detected in the PRB materials. These results are broadly comparable to laboratory based studies of arsenic removal by zerovalent iron, but additional complexity is revealed in the field environment, which is largely due to the influence of subsurface microbiota.
