Treatment of groundwater polluted by arsenic compounds by zero valent iron.

Batch experiments were carried out to study the kinetics and efficiency of inorganic arsenic removal by zero valent iron (ZVI) powder, and as well as the effects of pH, anions, and humic material (HM) on this process. Moreover, column experiment was conducted for 31 days to treat arsenate solution of 500 microg As/L using waste iron chippings as filling. Batch experiments showed that both arsenate and arsenite compounds could be removed efficiently from simulated groundwater by ZVI under aerobic and relative anaerobic conditions. Aerobic condition was favorable to arsenic removal especially for arsenate, while arsenite could be removed more rapidly than arsenate in relative anaerobic condition. Oxidation of arsenite to arsenate by iron species in aerobic environment was observed, which is thought to be an important pathway of arsenite removal. In an unsealed system, the removal efficiency of both arsenate and arsenite decreased at higher pH value. In a sealed system, acidic and alkaline condition seemed to be favorable for arsenate and arsenite removal, respectively. Phosphate and low concentration sulfate caused a decrease in arsenate removal, while high concentration sulfate as well as nitrate caused slight increase in arsenate removal. Presence of HM in solution slightly inhibited arsenic removal. Arsenic removal efficiency in column study was influenced by flow rate and work period of the column. More than 98% of arsenate could be removed stably with a hydraulic resident time of 2 h at last, and the effluent meet the drinking water standard.