UV-Improved Removal of Chloride Ions from Strongly Acidic Wastewater Using Bi2O3: Efficiency Enhancement and Mechanisms

Strongly acidic wastewater generated from nonferrous metal smelting industries can be recycled as sulfuric acid after the contaminants have been removed, and among which, Cl– is rather difficult to remove. Although previous studies showed that Cl– can be removed from acidic Zn electrolyte by Bi2O3, this method still suffers from low efficiency when being employed for strongly acidic wastewater recycling. Otherwise, very high Bi2O3 dosage and H2SO4 concentration are required, leading to the need for improvement. In this study, UV irradiation was employed to improve the removal, and it was found that Cl– removal efficiency was substantially enhanced from 63.9 to 98.3%, the optimum Bi2O3/Cl– mole ratio was lowered from 1.5:1 to 0.5:1, and to achieve the maximum removal efficiency, the required H2SO4 concentration was lowered from 70 to 40 g/L. The mechanisms were also elaborated. First, Bi2O3 dissolves under the function of UV and H+, and the produced Bi3+ combines with H2O and Cl– to form BiOCl. Then, Bi2O3/BiOCl transforms into BiOCl(h+)/Bi2O3(e–) under UV irradiation, and the generated h+ oxidizes Cl– to Cl•. Finally, Cl• reacts with Bi2O3/e– to produce BiOCl. This study offered a theoretical foundation for the improvement of Cl– removal from strongly acidic wastewater.