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CHEMICAL INTERACTIONS OF ARSENATE, ARSENITE, PHOSPHATE, AND SILICATE WITH IRON (II, III) HYDROXYCARBONATE GREEN RUST
SU, C. AND R. T. WILKIN. CHEMICAL INTERACTIONS OF ARSENATE, ARSENITE, PHOSPHATE, AND SILICATE WITH IRON (II, III) HYDROXYCARBONATE GREEN RUST. Presented at RTDF Permeable Reactive Barriers Team Meeting, Charleston, SC, October 11 - 12, 2006.
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Granular zerovalent iron has been proposed to be used as a medium in permeable reactive barriers (PRBs) to remove arsenic from contaminated groundwater. Iron(II, III) hydroxycarbonate green rust (carbonate green rust, or CGR) is a major corrosion product of zerovalent iron under anaerobic conditions. CGR is also found in certain hydric soils and sediments. It is important to study the chemical interactions of inorganic arsenic species (arsenate and arsenite) and common oxyanions (phosphate and silicate) with this green rust in order to understand the behavior and fate of these anions in groundwater systems. To maximize the effectiveness of iron barriers, it is essential to evaluate the influence of geochemical parameters such as arsenic concentration, pH, and time on the interactions of arsenic with iron corrosion products. CGR was synthesized in the laboratory by neutralizing ferrous sulfate solution with sodium hydroxide and sodium carbonate or sodium bicarbonate followed by air sparging. The synthetic products were characterized with X-ray diffraction (XRD), thermogravimetric analysis, scanning electron microscopy, Fourier transform infrared spectroscopy, and wet chemical analysis. Batch arsenic sorption experiments were conducted with arsenate and arsenite in an anaerobic glovebox. The pH values ranged from 8 to 10.5. Both arsenate and arsenite sorption increased with increasing time up to 30 days. Arsenite showed much higher sorption than arsenate. Adsorbed arsenite (up to 90 mg kg-1) was partially oxidized on solid surface as determined by arsenic speciation analysis of sorbed arsenic extracted with hydrochloric acid. X-ray absorption near edge structure spectroscopy results confirmed partial oxidation of arsenite by CGR.
Record Details:Record Type: DOCUMENT (PRESENTATION/POSTER)
Organization:U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RESEARCH AND DEVELOPMENT
NATIONAL RISK MANAGEMENT RESEARCH LABORATORY
GROUND WATER AND ECOSYSTEMS RESTORATION DIVISION
SUBSURFACE REMEDIATION BRANCH