OXIDATIVE ADSORPTION OF INORGANIC ARSENITE (As[Ⅲ]) WITH γ-Al_2O_3 AND MnO_2

摘要

The oxidation of inorganic arsenite As(Ⅲ) with MnO_2 was investigated to improve the removal of As(Ⅲ) from aqueous solution. Adsorbent γ-Al_2O_3 and the oxidation agent MnO_2 were used to oxidize As(Ⅲ) to arsenate As(Ⅴ) and to remove arsenic as As(Ⅴ) in the adsorption step. It is known from previous research that As(Ⅴ) is adsorbed and removed more easily than As(Ⅲ). The removal of As(Ⅲ) from aqueous solution with the mixture of γ-Al_2O_3 and MnO_2 was carried out to investigate the effects of pH and the additional amount of MnO_2 on the removal of As(Ⅲ). The removal of As(Ⅲ) was increased from 20% to 90% at pH3 in the presence of MnO_2. The Mn~(2+) was dissolved to oxidize As(Ⅲ) to As(Ⅴ) in the aqueous solution due to the oxidation reaction of As(Ⅲ) with MnO_2. As(Ⅲ) exists as a non-charged species, H_3AsO_3, below pH9, whereas As(Ⅴ) exists as anionic species, H_3AsO_3~-, HAsO_3~(2-) and AsO_4~(3-), above pH2. The isoelectric point of γ-Al_2O_3 is at pH8.6. The As(Ⅴ) is easily adsorbed with γ-Al_2O_3 due to the electrostatic interaction between anionic As(Ⅴ) and γ-Al_2O_3 with a positive zeta potential. The removal of As(Ⅲ) was considered to be improved by oxidizing As(Ⅲ) to As(Ⅴ) and adsorbing As(Ⅴ).