Mechanism of Germanium Adsorption by Iron Hydroxide Colloids during the Leaching Process of Secondary Zinc Oxide

In the leaching process of secondary zinc oxide, there is a problem of germanium loss caused by the colloidal adsorption of germanium by iron hydroxide (Fe(OH)₃) formed by Fe³⁺ hydrolysis. In response to this, this article elucidates the hydrolysis conditions of Fe³⁺ and the adsorption mechanism of the Fe(OH)₃ colloid on germanium through theoretical analysis and simulation of the adsorption process. The coexistence of Fe³⁺ and H₂GeO₃ requires high acidity conditions (pH < 1.53 at 25 °C). The adsorption of germanium by the Fe(OH)₃ colloid is a spontaneous exothermic entropy reduction process, which conforms to a pseudo-second-order kinetic model and includes three stages: fast, slow, and equilibrium. In addition, the adsorption process can be fitted by the Langmuir isotherm adsorption model, mainly consisting of monolayer and chemical adsorption. The Fe(OH)₃ colloid has a great adsorption capacity for germanium at 328 K, and the equilibrium adsorption capacity is 261.15 mg/g in 40 min. During leaching, the adsorption of germanium by Fe(OH)₃ colloids can be inhibited by increasing the reaction temperature, controlling the pH value of the solution system, and suppressing the formation of Fe³⁺ at the source. This study provides direction for how to suppress the adsorption of germanium by Fe(OH)₃ colloids during the leaching process of secondary zinc oxide, which is of great significance for improving the germanium leaching efficiency and fully utilizing limited germanium resources.