China Nonferrous Metallurgy

The chromium in the electroplating sludge occurred mainly in forms of oxides and/or hydroxides, which could be recovered through a combined process of Na₂CO₃ assisted oxidizing roasting and water leaching in this research. The results show under the condition of Na₂CO₃ amount of 100%, roasting temperature of 700℃, and roasting time of 90min, the Cr recovery rate reached 97.8% in the subsequent water leaching process; in a certain range, the Cr recovery rate increased with the increase of Na2CO3 amount, roasting temperature and time; in the Na₂S reduction of Na₂CrO₄ leaching solution, the chromium yield increased with the increase of the amount of Na₂S addition, reaction temperature and reaction time; however, excessive Na₂S amount would increase the pH of the leaching solution, resulting in the reverse dissolution of Cr₂O₃ and the decrease of chromium recovery; under the optimized condition of reaction temperature of 60℃, n(CrO^2-₄)/n(S^2-) of 8∶9, and reaction time of 80min, the chromium recovery reached 92.3%. The study achieved an efficient recovery of chromium from electroplated sludge.