The Effect of Fluid Acidity on GeO2 Solubility and Complexation in Aqueous Solutions and Its Implications on Ge Mineralization

Germanium (Ge) has been recognized as a critical strategic metal due to its high-technology implications. It is predominantly found in sphalerite within the Pb-Zn deposits, whose genesis is closely related to chloride-bearing hydrothermal activities. However, the dissolution and complexation of Ge in chloride-bearing fluids have not yet been well understood. To address this issue, this study investigates the dissolution behavior of Ge and corresponding species in HCl and NaCl aqueous solutions at 150 °C using the solubility method. The results show that the solubility of Ge in HCl solutions reaches 300 ppm and decreases with increasing HCl concentration. In contrast, the solubility of Ge in NaCl solutions is up to 1500 ppm and exhibits no significant dependence on NaCl concentration. The new findings demonstrate that the solubility of Ge in chloride-bearing solutions is primarily controlled by the solution’s pH. As the pH increases, the concentration of Ge dissolved in solutions rises substantially, suggesting that alkaline fluid environments facilitate Ge dissolution and transport. Further analysis of the experimental data indicates that the dominant species of Ge is Ge(OH)40 in acidic chloride-bearing solutions and Ge(OH)5− in neutral-basic chloride-bearing solutions, in which the species Ge(OH)5− promotes higher Ge solubility compared to Ge(OH)40. On account of high solubility in both HCl and NaCl solutions, it is proposed that Ge mineralization is not controlled by the co-precipitation process with Pb and Zn but by subsequent solid–liquid reaction between sphalerite and fluids. These experimental data and computational results not only provide new insights into the dissolution, transport, and precipitation processes of Ge in Earth’s material cycling but also offer novel perspectives for the understanding of Ge mineralization and industrial extraction and recovery of Ge.