Arsenic(III) and Arsenic(V)\nReactions with Zerovalent Iron\nCorrosion Products

Abstract

Zerovalent iron (Fe⁰) has tremendous potential as a\nremediation material for removal of arsenic from groundwater\nand drinking water. This study investigates the speciation\nof arsenate (As(V)) and arsenite (As(III)) after reaction\nwith two Fe⁰ materials, their iron oxide corrosion products,\nand several model iron oxides. A variety of analytical\ntechniques were used to study the reaction products\nincluding HPLC-hydride generation atomic absorption\nspectrometry, X-ray diffraction, scanning electron microscopy-energy-dispersive X-ray analysis, and X-ray absorption\nspectroscopy. The products of corrosion of Fe⁰ include\nlepidocrocite (γ-FeOOH), magnetite (Fe₃O₄), and/or maghemite\n(γ-Fe₂O₃), all of which indicate Fe(II) oxidation as an\nintermediate step in the Fe⁰ corrosion process. The in-situ\nFe⁰ corrosion reaction caused a high As(III) and As(V)\nuptake with both Fe⁰ materials studied. Under aerobic\nconditions, the Fe⁰ corrosion reaction did not cause As(V)\nreduction to As(III) but did cause As(III) oxidation to\nAs(V). Oxidation of As(III) was also caused by maghemite\nand hematite minerals indicating that the formation of\ncertain iron oxides during Fe⁰ corrosion favors the As(V)\nspecies. Water reduction and the release of OH^- to solution\non the surface of corroding Fe⁰ may also promote As(III)\noxidation. Analysis of As(III) and As(V) adsorption complexes\nin the Fe⁰ corrosion products and synthetic iron oxides\nby extended X-ray absorption fine structure spectroscopy\n(EXAFS) gave predominant As−Fe interatomic distances\nof 3.30−3.36 Å. This was attributed to inner-sphere, bidentate\nAs(III) and As(V) complexes. The results of this study\nsuggest that Fe⁰ can be used as a versatile and economical\nsorbent for in-situ treatment of groundwater containing\nAs(III) and As(V).