Arsenic(III) Remediation from Contaminated Water by Oxidation and Fe/Al Co-Precipitation

Battery grade γ-MnO2 powder was investigated as an oxidant and an adsorbent in combination with Fe/Al coagulants for removal of arsenic from contaminated water. Simultaneous oxidation of As(III) and removal by coprecipitation/adsorption (one step process) was compared with pre-oxidation and subsequent removal by coprecipitation/adsorption (two step process). The rate of As(III) oxidation with MnO2 is completed in two stages: rapid initially followed by a first order reaction. As(III) is oxidised to As(V) by the MnO2 with a release of approximately 1:1 molar Mn(II) into the solution. No significant pH effect on oxidation of As(III) was observed in the pH range 4 6. The rate showed a decreasing trend above pH 6. The removal of As(V) by adsorption on the MnO2 decreased significantly with increasing pH from 4 to 8. The adsorption capacity of the γ-MnO2 with particle size 90% passing 10 μm was determined to be 1.5 mg/g at pH 7. MnO2 was found to be more effective as an oxidant for As(III) in the two step process than in the one step process.