Synergistic SO2/H2SO4-Driven Co-Recovery of Zinc and Germanium from Industrial Dust: A Closed-Loop Strategy for Critical Metal Recycling

The generation of Ge-containing dust (GCD) during Zn hydrometallurgy raises considerable toxicity concerns; however, GCD contains useful metals, such as Zn, Ge, and Pb. The unique characteristics of Ge often result in the formation of specific Ge compounds within GCD, which manifest as either independent insoluble phases or inclusions, which complicates their separation and recovery. To address the challenges associated with the traditional recovery methods, this study proposes a novel process that utilizes SO2 reduction in conjunction with H2SO4 to extract Zn and Ge from GCD. The introduction of SO2 facilitates the conversion of insoluble materials through reduction reactions. A high SO2 flow rate enhances its interaction with the solid surface, thereby promoting continuous peeling and improving the reaction efficiency. The key parameters influencing the leaching rate of Zn and Ge, and the toxicity of the resulting reaction residue, include the initial acidity, liquid–solid ratio, duration of SO2 exposure, reaction temperature, and reaction time. Experimental findings indicate that SO2-promoted H2SO4 leaching outperforms the conventional methods, achieving increases of 3% and 12% in the leaching rates of Zn and Ge, respectively. Furthermore, the concentration of toxic metals in the residue is reduced to suitable levels post-reaction. The resultant Pb residue can be reintegrated into the Pb-recovery process for further utilization. In conclusion, the SO2-promoted H2SO4-leaching method represents a promising and environmentally sustainable approach for the recovery of useful metals from GCD.