Zerovalent iron (Fe0) has tremendous potential as a remediation material for removal of arsenic from groundwater and drinking water. This study investigates the speciation of arsenate (As(V)) and arsenite (As(III)) after reaction with two Fe0 materials, their iron oxide corrosion products, and several model iron oxides. A variety of analytical techniques were used to study the reaction products including HPLC-hydride generation atomic absorption spectrometry, X-ray diffraction, scanning electron microscopy-energy-dispersive X-ray analysis, and X-ray absorption spectroscopy. The products of corrosion of Fe0 include lepidocrocite (gamma-FeOOH), magnetite (Fe3O4), and/or maghemite (gamma-Fe2O3), all of which indicate Fe(II) oxidation as an intermediate step in the Fe0 corrosion process. The in-situ Fe0 corrosion reaction caused a high As(III) and As(V) uptake with both Fe0 materials studied. Under aerobic conditions, the Fe0 corrosion reaction did not cause As(V) reduction to As(III) but did cause As(III) oxidation to As(V). Oxidation of As(III) was also caused by maghemite and hematite minerals indicating that the formation of certain iron oxides during Fe0 corrosion favors the As(V) species. Water reduction and the release of OH- to solution on the surface of corroding Fe0 may also promote As(III) oxidation. Analysis of As(III) and As(V) adsorption complexes in the Fe0 corrosion products and synthetic iron oxides by extended X-ray absorption fine structure spectroscopy (EXAFS) gave predominant As-Fe interatomic distances of 3.30-3.36 A. This was attributed to inner-sphere, bidentate As(III) and As(V) complexes. The results of this study suggest that Fe0 can be used as a versatile and economical sorbent for in-situ treatment of groundwater containing As(III) and As(V).

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Elevated concentrations of U are found in agricultural drainage waters from the San Joaquin Valley, CA, which are often disposed of in evaporation basins that are frequented by waterfowl. To determine the factors that affect aqueous U concentrations in the basins, sorption experiments with U(VI) were performed at various CO2 partial pressures, dissolved Ca, Mg, and P concentrations, and carbonate alkalinities. Synthetic waters, comparable in inorganic constituents to irrigation and drainage waters, were prepared, spiked with 0.1 (soil) and 2 mg U(VI) L−1 (synthetic goethite), and analyzed for U, P (when applicable), and major ions. Total chemical analyses were input into the computer program FITEQL to determine U(VI) speciation and generate U(VI) adsorption constants with the diffuse layer model (also referred to as the two‐layer model). Maximum adsorption occurred in solutions with low carbonate alkalinities (≤3 mmol L−1), ionic strengths (≤0.03 M), Ca concentrations (≤4 mmol L−1), and P concentrations (<0.005 mmol L−1 for soil). Lesser and negligible adsorption was attributed to the predicted formation of highly soluble, negatively charged U(VI) carbonates [UO2(CO3)2−2 and UO2(CO3)4−3] that did not strongly adsorb to soil surfaces. Calcium and, to some degree, Mg competition with positively charged U(VI) species for surface sites was observed at low carbonate alkalinities (<3 mmol L−1 for goethite; <14 mmol L−1 for soil). At high carbonate alkalinities, carbonates competed with anionic U(VI) species for adsorption sites. Study results suggest that elevated U concentrations in the drainage waters are due to the speciation of dissolved U(VI) into negatively charged carbonate complexes.