Abstract:Electroplating sludge, a hazardous waste generated during the treatment of electroplating wastewater, poses significant environmental hazards but is rich in heavy metal elements such as copper, nickel, chromium, iron, and zinc, making it a valuable secondary resource. Currently, many scholars have conducted research on the harmless disposal and resource utilization of electroplating sludge. Harmless disposal methods primarily include solidification/stabilization (S/S) and thermal treatment technologies, while resource utilization mainly encompasses hydrometallurgical leaching, pyrometallurgy-hydrometallurgy combined processes, pyrometallurgy, and materialization. Solidification/stabilization technology is significantly effective in solidifying heavy metals in electroplating sludge. However, the addition of solidifying agents increases the total mass and volume of the sludge, thereby elevating landfill burden and costs. This method is suitable for electroplating sludge containing various stable pollutants. Thermal treatment technology can improve metal fixation efficiency and achieve volume reduction of electroplating sludge, but the treatment process causes environmental pollution and increases the porosity of sintered products, limiting their reuse. Additionally, it leads to the waste of valuable metal resources. Hydrometallurgical recovery of valuable metals from electroplating sludge includes acid leaching, ammonia leaching, bioleaching, etc. Acid and ammonia leaching can recover multiple valuable metals in stages, but acid leaching faces challenges in pH regulation for separation and adaptability issues with ultrasonic-assisted processes. Ammonia leaching requires careful control of ammonia volatilization, while bioleaching is constrained by microbial strains, resulting in unstable leaching efficiency and cycles. The pyrometallurgy-hydrometallurgy combined process converts metals such as copper, nickel, and zinc in electroplating sludge into corresponding chlorides that volatilize during roasting, and transforms chromium into water-soluble phases for recovery during leaching. However, this method is limited by corrosion issues with roasting equipment, restricting its industrial application. Moreover, the high roasting temperature leads to elevated energy consumption. Pyrometallurgical processes utilize high temperatures to reduce metal oxides in sludge and recover them in the form of multi-element alloys. Different reducing agents can be selected based on the composition of the sludge. The key to this method lies in selecting appropriate additives to form a low-melting slag system. Materialization technology primarily uses hydrometallurgical or pyrometallurgical techniques to targetedly convert metal elements in electroplating sludge into functional materials such as adsorbents, catalysts, and pigments. This method features a simple process, easy operation, and is more environmentally friendly and cost-effective for resource utilization, showing broad application prospects. However, due to the complex composition of electroplating sludge, in-depth research is required to investigate the migration patterns of other heavy metals, chlorine, organic pollutants, sulfur, and other potential hazardous substances beyond target elements, as well as their influence on the performance of target materials. In practical resource utilization processes, the selection of technological methods should be based on the composition of the sludge. For single-component electroplating sludge, hydrometallurgical and materialization technologies are prioritized to reduce process energy consumption and equipment investment costs. For complex multi-metallic electroplating sludge, pyrometallurgical recovery technologies or combined pyrometallurgy-hydrometallurgy processes are preferred to achieve resource utilization while avoiding environmental risks associated with multi-metal separation in single hydrometallurgical processes.
