Removal of arsenic from effluents -: A comparison between the FeSO4/Air and FeSO4/H2O2 systems

This paper reports the results of kinetic studies involving the precipitation of arsenic From aqueous solutions as FeAsO4/Fe(OH)(3), using FeSO4 as source of Fe ions, and Air or H2O2 as oxidizing agents. Both systems lead to an efficient removal of arsenic. The differences in oxidants performances are in the precipitation reaction rate - much faster using hydrogen peroxide. Mechanisms of reactions were suggested based on the following main steps: Fe(II) oxidation: 2 Fe2+ + 1/2 O-2 + 2 H+ = 2 Fe3+ + H2O 2 Fe2+ + H2O + 2 H+ = 2 Fe3+ + 2 H2O As(III) oxidation: HAsO2 + 2 Fe3+ + 2 H2O = 2 Fe2+ + H3AsO4 + 2H(+) HAsO2 + H2O2 = H3AsO4 Precipitation: Fe3+ + H3AsO4 = FeAsO4 (s) + 3 H+ H3AsO4 + n Fe(OH)(3) (s) = H3AsO4 (ads) [Fe(OH)(3)](n) (s).