Gallium and germanium leaching from jarosite cake by organic acid: a combined experimental and DFT approach

Hydrometallurgical zinc plant residues are recognized as a significant environmental hazard due to the potential for heavy metals and acids to dissolve upon exposure to rainwater. This process allows contaminants to infiltrate soil and groundwater, posing a threat to aquatic systems and ecosystems. To address these environmental concerns, a hydrometallurgical leaching process has been developed for the non-toxic co-treatment of jarosite cake (JC), to prevent pollution while enabling the efficient extraction of valuable metals. In this study, an innovative approach for the leaching of gallium (Ga) and germanium (Ge) from JC was developed using organic acids, specifically oxalic and citric acid. The effects of various process parameters, including operating temperature, solid-to-liquid ratio, acid concentration, and leaching duration, were examined and optimized. Under optimal conditions, extraction efficiencies of 96.0 ± 0.6 % for Ga and 79.0 ± 3.8 % for Ge were achieved. To further understand the leaching mechanism, density functional theory (DFT) calculations were performed to investigate the interactions of Ga and Ge with organic acids and water molecules. Geometric structure and electrostatic potential were considered in these calculations, and the crucial role of pH in the leaching process was identified. Both experimental analysis and DFT calculations confirmed that the leaching of Ga and Ge occurred through acidolysis and complexolysis mechanisms. Prior to leaching, mineral liberation analysis (MLA) was conducted, which indicated the presence of these metals in sulfate, silicate, and oxide phases within the JC. The results obtained in this study demonstrate that organic acid leaching can serve as an effective and environmentally sustainable method for the extraction of Ga and Ge from JC. This approach not only facilitates the recovery of valuable metals but also contributes to the mitigation of environmental risks associated with hydrometallurgical zinc plant residues.