Strongly acidic wastewater, which is usually generated from nonferrous metal smelting industries, has the ability to be recycled as sulfuric acid. Before this wastewater is recycled, the removal of chloride ions is necessary to improve the quality of the recycled sulfuric acid. At present, the widely used method to remove chloride ions from acidic wastewater in the form of CuCl precipitate has several disadvantages, including low removal efficiency, high temperature, long treatment time, and high dosage of Cu(II). This study proposed an improved new method of removing Cl(−I) using Cu(0)/Cu(II) under UV irradiation, and the mechanism was investigated. The Cl(−I) concentration was lowered to below 50 mg/L at a Cu(II) dosage of 1200 mg/L. Under UV irradiation, ligand-to-metal charge transfer takes place, thereby resulting in the formation of Cl • . Next, CuCl precipitates form through the reaction between Cu(0) and Cl • and produce h + / • OH under UV irradiation, which can oxidize Cl(−I) to Cl • . Simultaneously, Cl 2 gas also forms directly from Cl • . This study offered a theoretical foundation for the application of UV irradiation for the enhanced removal of chloride ions from strongly acidic wastewater.

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.

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