Inorganic arsenic removal by zero-valent iron

Zero-valent iron can be used to remove inorganic arsenic from aqueous solutions. The mechanism for arsenic removal appears to be a surface precipitation or adsorption of arsenic with iron. This mechanism differs significantly from the removal mechanisms of chlorinated hydrocarbons (reductive dechlorination) and chromium(VI) reduction accompanied by hydroxide precipitation. Arsenic removal efficiencies of greater than 95% are observed in laboratory and field-column studies. Arsenate is removed more effectively than arsenite; however, effective arsenite removal occurs even under anoxic conditions. The removal efficiency is related to the surface area or the type of iron used and improved over time, possibly due to pitting of the iron surface and increased surface area for sorption due to iron corrosion and ferrous iron adsorption/precipitation. Preliminary results indicate that arsenic is tightly bound to the iron filings, and only a small percentage is readily leached. This finding coupled with the results of field experiments and spectroscopic analysis (SEM/EDX and XPS) provide evidence that surface precipitation is the predominant removal mechanism.