Nitric acid dissolution of germanium overlay in hard zinc slag to enhance germanium leaching and optimization of response surface methodology

With the rapid development of global digital economy and aerospace, the gap between the supply and demand of germanium is expanding, and the establishment of a new process for the deep leaching of germanium from hard zinc slag is imminent. In this paper, on the basis of analyzing the reasons for the low germanium leaching rate from hard zinc slag, a new process of germanium leaching enhanced by HNO3 dissolution of externally wrapped ZnFe2O4 is established, and response surface optimization is carried out. The PbggGe4O7 phase in hard zinc slag is externally wrapped with ZnFe2O4 phase, and the non-reaction between ZnFe2O4 and hydrochloric acid is the main reason for the low leaching rate of germanium from hard zinc slag, so it is necessary to add HNO3 to dissolve the external ZnFe2O4 in leaching, and then use hydrochloric acid to leach the PbGe4O7 containing germanium in the interior. The potential pH diagram of the Pb-Ge-Cl-H2O system was also plotted, indicating that increasing the concentration of chloride ions during hydrochloric acid leaching contributes to the generation of GeCl4 at low acidity. When the hydrochloric acid concentration was 134.65 g/L, the liquid–solid ratio was 6, the theoretical dosage of HNO3 was 0.3, and the leaching time was 236 min, the optimum leaching rate of germanium was 93.72%, which was 23.72% higher than that of germanium leaching from hard zinc slag.