Arsenate and Arsenite Sorption on and Arsenite Oxidation by Iron(II, III) Hydroxycarbonate Green Rust

Abstract

Iron(II,III) hydroxycarbonate green rust is a major corrosion product of zerovalent iron that is being used in permeable reactive barriers to remediate groundwater arsenic contamination. To optimize the design of iron barriers, it is important to evaluate the influence of geochemical parameters such as pH, time, and arsenic concentration on the interactions of arsenic with iron corrosion products. We synthesized iron(II, III) hydroxycarbonate green rust by neutralizing FeSO 4 solution with NaOH and Na 2 CO 3 or NaHCO 3 followed by air sparging. The synthetic products were characterized with scanning electron microscopy, X-ray diffraction, and wet chemical analysis. We conducted batch sorption experiments with arsenate and arsenite in an anaerobic glovebox. The pH ranged from 7.5 to 10.7. Both arsenate and arsenite sorption increased with increasing time up to 60 days. More arsenite was sorbed at pH 7.5 than at pH 10.4. Arsenite showed much higher sorption than arsenate. Sorbed arsenite (up to 90 g kg - 1 ) was partially oxidized at the surface of carbonate green rust. Oxidation of sorbed arsenite could be advantageous because arsenate is generally less toxic and less mobile than arsenite.