Removal of Chloride from Sulfuric Acid Wastewater by Na2SO3 and Cu(II) Based on the Process of Reduction and Precipitation

Nonferrous metal smelting enterprises generate large volumes of sulfuric acid (H2SO4) wastewater annually, which contains chloride (Cl−), fluoride (F−), arsenic, and heavy metal impurities. Currently, recycling has become a research hotspot in the field of H2SO4 wastewater treatment, involving two key processes, purification and concentration. Among the various technologies for selective removal of different impurities, the mature technologies for Cl− remain insufficient. In this study, a Cl− removal method based on the “reduction and precipitation” mechanism of copper [Cu(II)] and sodium sulfite (Na2SO3) was proposed. The efficiency, solid product and intermediate species composition, mechanism, and actual application were systematically investigated. For simulated wastewater, the Cl− removal efficiency reached 96.8% under optimized conditions. During the treatment process, Cu(II) is first reduced by Na2SO3 to generate cuprous [Cu(I)], which then precipitates with Cl− to produce cuprous chloride (CuCl). Excessive Na2SO3 can trigger side reactions, producing cuprous sulfite (Cu2SO3) and sulfur dioxide (SO2); therefore, precise control of Na2SO3 dosage is critical.