2026 Kim Selective chromium recovery from electroplating sludge

Electroplating sludge (ES) is a hazardous waste containing valuable metals such as chromium (Cr), nickel (Ni), and copper (Cu). This study aimed to investigate the selective recovery of Cr from ES through alkaline roasting coupled with water leaching. A thermodynamic analysis revealed that the conversion of Cr(OH)3 to Na2CrO4 is possible at the solid-gas-alkali interface. The effects of various parameters, including roasting time, NaOH/sludge mass ratio, and roasting temperature, on chromium conversion were systematically evaluated. Results indicated that chromium leaching efficiency improved with extended roasting time, reaching maximum efficiency of 96.8% at 400°C after 4 hours with a NaOH/sludge mass ratio of 1.0. Beyond this ratio, higher alkali concentration led to the formation of competing phases such as NiCr2O4. Additionally, roasting temperatures above 500°C contributed to insoluble chromium phases. This process effectively removed Cr while retaining over 99% of Ni and Cu in the solid residue, facilitating the production of an intermediate feedstock rich in Ni and Cu for potential downstream recovery applications.