Removal Efficiency and Mechanism for Cl− from Strongly Acidic Wastewater by VC-Assisted Cu2O: Comparison Between Synthesis Methods

The discharge of strongly acidic industrial wastewater containing high concentration of chloride ions (Cl^-) has become one of the major environmental challenges faced globally. For the removal of extremely stable Cl^- in acidic aqueous conditions, precipitation method possesses major advantages of strong adaptability and simple operation. This study proposed a novel cuprous oxide (Cu₂O) method assisted by ascorbic acid (VC) for the removal of Cl^- from strongly acidic wastewater. First, liquid-phase reduction was chosen as the optimal Cu₂O synthesis method based on product purity and composition. Then, parameter optimization results show that increased reagent dosage and acidity significantly enhanced Cl^- removal efficiency, while other factors had negligible impacts. After treatment with the sole addition of Cu₂O, the dosed Cu₂O existed in four forms, including cuprous chloride (CuCl), copper ion (Cu²⁺), elemental copper (Cu⁰), and Cu₂O, among which the generation of Cu²⁺ and Cu⁰, through the oxidation and disproportionation of cuprous ion (Cu⁺), served as the main reason for the unsatisfactory efficiency in the removal of Cl^-. Fortunately, VC is precisely capable of inhibiting the side reactions of Cu⁺, and under the assistance of 0.10 g VC, the removal of Cl^- by Cu₂O was greatly improved with the multiple of theoretical reagent dosage decreasing from 12 to 3, the residual concentration of Cu²⁺ decreasing from 1197 to 18.4 mg/L and the residual concentration of Cl^- decreasing from 88.4 to 53.8 mg/L, thus validating the feasibility of this method.