Competition effect between AsO2− and NH4+ in oxidation system

Abstract

The environmental effects of characteristic pollutants arsenite (AsO2−) and ammonium (NH4+) produced in the process of tungsten smelting cannot be ignored. Through the ozonation experiment of AsO2− and NH4+, it is confirmed that AsO2− with lower redox potential (-0.560 V) is more readily oxidized than NH4+ (-0.283 V), leading to the coexistent AsO2− inhibiting the ozonation of NH4+. In order to improve the oxidation efficiency of NH4+, prepared CeO2-MnO2 composite metal oxide catalysts before and after reaction were characterized by SEM, EDS, FT-IR technics, and investigated for the catalytic ozonation of wastewater containing AsO2− and NH4+. When the initial AsO2− concentration is maintained at 2 mg/L and the NH4+ concentration increases from 25 to 150 mg/L, the conversion of AsO2− to AsO43− remains above 97%, while the NH4+ removal rate decreases from 94.38% to 47.01%, in which confirms the competitive effect of AsO2− oxidation prior to NH4+. Moreover, the test of catalyst dosage reconfirms the result of AsO2− oxidation superior to NH4+, and the optimum catalyst dosage is 1.5 g/L. After the test of tert-butyl alcohol (TBA), the possible oxidation mechanism is proposed that AsO2− is oxidized primarily by O3, whereas the oxidation of NH4+ is mainly ascribed to the hydroxyl radical (·OH) obtained from catalytic decomposition of O3 by CeO2-MnO2 composite metal oxide catalysts.

Keywords

• AsO2−
• NH4+
• CeO2-MnO2
• Competition effect
• Catalytic ozonation