Effect of metals on the oxidation of As(III) with H2O2

The influence of a number of metals (Cu2+, Fe2+, Fe3+, Pb2+, Cd2+, Ni2+, Zn2+, Mn2+) on the oxidation rates of As(III) with H2O2 have been measured in dilute NaCl solutions. Similar measurements were made in natural seawater, which includes the effect of major cations and anions on the rates. Among the metals studied, copper and iron caused large increases in the oxidation rates at concentrations which may occur in freshwaters, while lead may have an effect in heavily polluted systems. Increases in the rates were linear at low concentrations of metals and tended to be non-linear at high concentration, possibly due to the reactions of various metal–arsenite species with H2O2. Fe produced slightly different effects on the overall kinetic constants and marked differences on the sorption of As(III) on Fe oxyhydroxides depending on whether Fe(II) or Fe(III) were spiked in the solutions. To apply these rates in natural waters, one must consider the presence of competing inorganic and organic ligands, which may diminish the formation of metal–arsenite complexes.