Removal of arsenic from an aqueous solution by coprecipitation with manganese oxide

The removal of arsenic (As) from wastes is important to ensure good environmental practice within the nonferrous metallurgical industry. In the present study, the coprecipitation of As and manganese was investigated as a possible means of achieving such removal. As(V) was found to be removed from a Mn–As(V) aqueous solution during stirring. Such removal of As(V) from an aqueous solution is likely caused by coprecipitation with Mn3O4 and Mn(OH)2, both of which are assumed to have isoelectric pH of 10.9. Higher removal of As(V) from an aqueous solution was found at pH of 6–10, and can be attributed to the adsorption of H2AsO4− and HAsO42− onto the positively charged surface of Mn3O4 and Mn(OH)2, which is caused by electrostatic interaction. Conversely, the lower removal of As(V) from an aqueous solution at a pH of 11 can be attributed to the electrostatic repulsion between As(V) species and the negatively charged surfaces of Mn3O4 and Mn(OH)2.