Oxidation of arsenite in groundwater using ozone and oxygen

Oxidation of arsenite wAs III.x with ozone and oxygen was investigated in groundwater samples containing 46]62 mgrl total dissolved arsenic, 100]1130 mgrl Fe and 9]16 mgrl Mn. Conversion of As III., which constituted over 70% of dissolved arsenic in the samples, to As V. was fast with ozone, but sluggish with pure oxygen and air. Iron and manganese in the samples were also oxidized and, by sequestering the resultant As V., played a significant role in the rate of reaction. Sorption capacity of freshly precipitated Fe OH.3 was estimated to be 15.3 mg Asrg. The kinetics of As III. oxidation were interpreted using modified pseudo-first-order reaction. Half-lives of As III. in experimental solutions involving saturation with each gas were approximately 4 min for the ozone reaction and, depending on the Fe concentrations, 2]5 days for pure oxygen and 4]9 days for air.