Kinetics of the arsenite oxidation in seepage water from a tin mill tailings pond

The kinetic of the oxidation of trivalent arsenic was investigated in synth etic as well as in natural samples of a tin mill seepage water. The influen ce of ferric ions and solid MnO2 on the process was studied. To determine t he time dependence of the concentrations of the arsenic species, a series o f samples were taken sequentially and analysed by coupling of ionchromatogr aphic separation and ICP-MS detection. To investigate the naturally occurri ng oxidation reaction, original seepage water samples were filtered and spi ked with As(III) (1 mg l(-1)) and Fe(II) (10 mg l(-1)) and shaken providing intensive contact with the air. Additional synthetic samples buffered with carbonate were used in similar experiments to simplify the system. The rea ction was incomplete in the presence of excess of iron for both types of sa mples. The oxidation of As(III) was complete within 8 h in the presence of MnO2 (10 mg), but there was a difference in oxidation rates between the nat ural and the synthetic samples. The results are discussed with respect to t he redox potentials and equilibrium constants. (C) 2000 Elsevier Science B. V. All rights reserved.