Recovering metals from flue dust produced in secondary copper smelting through a novel process combining low temperature roasting, water leaching and mechanochemical reduction

Flue dust from secondary copper smelting (FDSC) is a hazardous waste as well as a secondary resource due to the high content of Cl, Br, and valuable metals (Pb, Cu, Zn, Cd). Herein, a novel process, combined low-temperature roasting, water leaching, and mechanochemical reduction, was developed for recovering metals from the FDSC. The phase conversion and behavior of the main elements in the whole process were explored based on thermodynamic analysis, experimental research, and various characterization. First, thermodynamics calculation revealed that adding H2SO4 could significantly decrease the roasting temperature and promote the generation of soluble metal sulfates. The experimental results showed that more than 99% of Cl and Br were removed by roasting at 325 °C and 1.5 times H2SO4 addition. Subsequently, the Cu, Zn, and Cd were almost completely leached by water under the conditions of 80 ℃, 2 h and L/S = 5 mL·g-1, while Pb was rejected and enriched in the residue. Finally, using iron powder as a reductant, 96.7% of PbSO4 was reduced to elemental lead at room temperature with the aid of mechanical force. The findings illustrated that the recovery performance of metals and environmental benefits will be greatly improved by the proposed process.