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

Abstract

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.