Improvement of Carbothermic Reduction of Copper Smelting Slag and Valuable Constituents Recovery

In order to comprehensively utilize copper smelting slag, the effect of strengthening measures on the reduction rate of the copper smelting slag, reduction kinetics, magnetic separation of reduced pellet and volatilization of residual valuable constituents were investigated in the present study. Milling for mechanical activation was the most efficient method to improve the reduction rate of copper smelting slag compared to addition of Na2CO3 catalyst and high reactivity reducing agent. The metallization degree of reduced pellet increased from 54.5% to 75.5% when the slag-coal mixture was milled for 30 s and reduced at 1100°C for 30 min. The apparent activation energy for the reduction of milled pellet increased from 96.1 kJ/mol to 153.5 kJ/mol. The iron concentrate magnetically separated from the milled pellet reduced at 1200°C had the best quality. The removal rates of typical elements during direct reduction-magnetic separation decreased in the sequence of Zn>K>Na>Cu. Secondary-dust captured from the flue gas contained 70.17 mass% Zn and 11.99 mass% Pb, which could meet the requirements of I grade zinc ore. The Zn in the dust existed in the form of ZnO. The productivity of the dust was around 1.49%. The application of mechanical milling in the reduction of copper smelting slag/coal composite pellet can improve the reduction efficiency of iron oxide and the quality of Zn-rich secondary dust. This work can help to enhance the utilization of copper smelting slag in a more efficient and sustainable method.