Tentative Study On Arsenite Oxidation

Arsenic is a carcinogen and toxic to man and other living organisms, whichwidely distributed in water, soils and anthropogenic sources. The contamination ofdrinking-water supplies with inorganic arsenic is commonly reported and has beenidentified as a major risk for human health. Arsenic is present in natural water in twooxidation states, +3(As(Ⅲ)) and +5(As(Ⅴ)), which are charaterised by differentchemical behaviour, bioavailability, and toxicity. As(Ⅲ) is much more toxic thanAs(Ⅴ). Various treating methods such as ion exchange, adsorption and coagulationhave been proved to be feasible to As(Ⅴ) but ineffective to the removal of As(Ⅲ).Therefore, oxidation of As(Ⅲ) to As(Ⅴ) could not only enhance As(Ⅲ) removal butalso reduce its toxicity. This paper investigated two methods for oxidation of As(Ⅲ)including bio-oxidation and TiO2 photo-oxidation.Hydride generation-atomic absorption spectrometer is used in this study toquantify total arsenic and arsenite respectively at different pH conditions. The optimaloperation conditions were studied and established. The relative standard deviationsare 5.2% and 2.0%, while the reclaim rates are 89.4～105.6% and 96～100% forAs(Ⅲ) and total arsenic, respectively.Four strains were isolated from active sludge which could catalyze arsenicoxidation. The tolerance of strains to As(Ⅴ) is higher than that of As(Ⅲ). They cangrow in 1500 arsenate-contained or 500 mg/L arsenite-contained medium. Theoxidation of As(Ⅲ) by the stains can effectively conduct at 20~30℃ and 30.2%oxidation rate is reached at pH 6.Photocatalytic oxidation of arsenite by use of TiO2 was studied. The effect ofsome important parameters was investigated. A quite high oxidation rate 66.1% wasobtained under the conditions of 500W Hg lamp irradiation, 6 hours, TiO2 dosage1g/L,addition of 0.03% H2O2 , pH 8. A tentative study on photocatalytic oxidation ofarsenite mechanism was conducted. Furthermore, 40.7% photocatalytic oxidation rate iof arsenite using TiO2 was observed under the irradiation of sunlight.