Sorption and speciation of arsenic by zero-valent iron

Sorption and speciation of arsenic in groundwater remediation using zero-valent iron (ZVI) was investigated by batch and column experiments. In batch tests, arsenite was oxidized to arsenate which was favorably immobilized by co-precipitation with Fe(III)-bearing compounds as corrosion products, leading to the dominant surface species of As(V). In column materials after introducing influent with arsenite for 22 pore volumes(pvs), As(III) was predominant on the surface of ZVI in all segments of column, while intense oxidation of arsenite to arsenate was observed especially near the inlet. It is considered that the surface of ZVI granules was already uniformed and corrosion products are the most accumulated on ZVI granules near the inlet because ZVI has been contacted with high concentrations of arsenite for the longest time in the most bottom parts. This was also supported by the experimental results of XPS that relative intensity of O 1s peak assigned to oxide was the largest in the most bottom segment. Also XPS results revealed that arsenic was immobilized on ZVI granules mainly as arsenite and to a lesser extent arsenate. These observations suggest that the retention mechanism is primarily sorption rather than reduction. The results of geochemical calculations along with the SEM-EDX suggest that arsenite and arsenate were co-precipitated with mainly Fe(III)-bearing minerals and carbonates.