Efficient Recycling of Valuable Metals from Waste Copper Slag by Using Secondary Aluminum Dross as a Novel Reductant

In this work, an innovative and carbon-free smelting reduction process is proposed to recycle valuable metals from waste copper slag using secondary aluminum dross as a reductant. Experimental and thermodynamic investigations were carried out to understand the reaction and separation process and its correlation with smelting temperature, modified basicity (CaO/SiO 2 mass ratio), and dross/slag ratio. The interaction between MgO crucible and liquid slag was also revealed, which was found to have a critical role in metal recovery. The reduction rates of iron and copper are close to 100 pct, but their separation from slag during smelting is highly sensitive to temperature and basicity. Higher modified basicity (0.9 to 1.1) is essential to enhance the recovery of valuable metals because it can reduce both MgO dissolution and slag viscosity. At optimal conditions, 98.6 pct Fe and 98.3 pct Cu in the slag can be recovered as a high-purity alloy. Meanwhile, ~ 99 pct of hazardous elements in the slag have been removed by a reduction-evaporation mechanism. From the results, it is clear that aluminum dross is an efficient, green, and cost-effective reductant for copper slag, by which these two industrial wastes can be transformed into clean and value-added products.