Arsenic(III) and Arsenic(V) reactions with zerovalent iron corrosion products

Zerovalent iron (Fe-0) 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 Fe-0 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 Fe-0 include lepidocrocite (gamma-FeOOH), magnetite (Fe3O4), and/or maghemite (gamma-Fe3O4), all of which indicate Fe(II) oxidation as an intermediate step in the Fe-0 corrosion process. The in-situ Fe-0 corrosion reaction caused a high As(III) and As(V) uptake with both Fe-0 materials studied. Under aerobic conditions, the Fe-0 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 Fe-0 corrosion favors the As(V) species. Water reduction and the release of OH- to solution on the surface of corroding Fe-0 may also promote As(III), oxidation. Analysis of As(III) and As(V) adsorption complexes in the NO 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 Angstrom. This was attributed to inner-sphere, bidentate As(III) and As(V) complexes. The results of this study suggest that Fe-0 can be used as a versatile and economical sorbent for in-situ treatment of groundwater containing As(III) and As(V).