Phase evolution and elemental distribution of zinc and germanium during the sulfide roasting, zinc fuming and leaching processes: Benefit of pretreating zinc oxide dust

Germanium plays an essential role in many high-tech fields because of its excellent electrical and optical properties. As a zinc refining by-product, zinc oxide dust (ZOD) is one of the most important sources of germanium recovery. However, the low leaching efficiency of germanium seriously hinders germanium recovery. This study focuses on the phase evolution and elemental distribution of zinc and germanium during the zinc refining process by analyzing the occurrence state of zinc and germanium in products and the key factors and chemical reactions causing the loss of zinc and germanium during the process. In the sulfuric-acid leaching process without an oxidant, the sulfides encapsulating germanium cannot be leached, which resulted in a loss of germanium. In addition, the formation of an insoluble PbSO₄ coating layer and silica compounds during the sulfuric-acid leaching impeded the leaching reactions. Accordingly, pre-treatment by oxidative leaching with Fe³⁺ and the role of NaAc in dissolving PbSO₄ were tested. The efficiency of Ge recovery is approximately 30 % higher than that of the conventional leaching process.