The process of germanium–tannin complex is the oldest form of technology for extracting germanium from Ge-containing solutions. This reaction mechanism is relatively controversial as it imposes restrictions on ideas and methods for reducing the amount of tannin. In this paper, using SEM, TEM, FT-IR, XPS, NMR, TOF-SIMS and UV diffuse reflectance spectroscopy for a deep analysis of germanium–tannin complex, the mechanism of extracting germanium from Ge-containing solutions with tannins is investigated. The results show that the theoretical tannin complex mass is 30 times that of tannin mass, and the complex rate reaches 98.84%. The changes of -OH stretching band in FT-IR spectra, the emergence of C₃H₃GeO₇, C₂H₃GeO₆, and C₈H₇GeO₇ in TOF-SIMS images, and the shift of Ge and O banding energy in XPS detail spectra provided definitive evidence for the germanium–tannin complex process, highlighting that the formed complexes of tannins with germanium involve six coordinate Ge-O bonds, which are obtained through orthophenol hydroxyl groups in tannins reacting with Ge⁴⁺. Furthermore, the complex mode of germanium–tannins is layer polymerization, which finally forms an agglomeration of complex flocs. The findings of this research is innovative, and can have a profound impact on the future introduction of various methods to reduce the mass of tannins.

Zinc oxide dust from lead zinc smelting is an important raw material for germanium recovery. This article researched the behaviour of germanium and iron in zinc oxide dust leaching in response to the problem of low germanium leaching efficiency. For this purpose, the germanium phase distributions were confirmed, the effects of sulphuric acid concentration, liquid–solid ratio, leaching temperature, and leaching time were determined. According to the findings, germanium exists primarily in the form of soluble germanium oxide and germanates. In addition, the germanium leaching efficiency is most affected by the leaching time, because the leaching iron will be oxidised and create Fe₄Ge₃O₁₂ precipitation with the leaching germanium if the leaching time is too long, resulting in the decline of germanium leaching efficiency. The leaching efficiency of zinc and germanium can reach 89.05% and 84.32%, respectively, when the sulphuric acid concentration is 150 g/L, the liquid–solid ratio is 5:1, the leaching temperature is 85°C, and the leaching time is 30 min, which is 0.44% and 7.21% higher than that under unoptimised conditions. Furthermore, through sodium sulphite-assisted leaching, the leaching efficiency of germanium is further increased to 89.48%, indicating that reductant-assisted leaching is a direction worthy of study.

In recent years, with the development of science and technology, the strategic position of germanium is becoming more and more important, and the global demand for germanium is also increasing. At present, there is no unified description of the existence form of germanium in solutions. Based on the current mainstream acid leaching process of germanium, this paper studies the existing form and properties of germanium in sulfuric acid solutions. Through the characterization and analysis of Raman, FTIR, and XPS of three concentrations of pure germanium solution, it is clear that germanium mainly exists in the form of H₂GeO₃ and some Ge⁴⁺ in sulfuric acid solution. Through the Tyndall effect and zeta potential, it is determined that H₂GeO₃ exists in the form of colloid in sulfuric acid solution. With the increase of germanium concentration, H₂GeO₃ will polymerize in a sulfuric acid solution to form polygermanic acid, and the H₂GeO₃ colloidal dispersion system becomes more stable. This study clarifies the existing form and properties of germanium in sulfuric acid solution, which is of great significance to the leaching extraction of germanium-containing materials and the development of the germanium industry.

The acid mud produced in the nonferrous smelting process is a hazardous waste, which mainly consists of elements Hg, Se, and Pb. Valuable metal (Hg/Se/Pb) can be recovered from acid mud by heat treatment. For safe disposal of the toxic acid mud, a new resource utilization technology by microwave roasting is proposed in this paper. The reaction mechanisms were revealed through thermodynamics and thermogravimetric analysis, which showed that the main reaction was the oxidative pyrolysis of HgSe in the process of roasting. Moreover, the mercury removal effects of acid mud by microwave heating and conventional heating were studied, the recovery rate of mercury by microwave heating for 30 min at 400 °C was 99.5%: far higher than that of conventional heating for 30 min at 500 °C (44.3%). This was due to the high dielectric constant of HgSe, as microwaves can preferentially heat HgSe and reduce the adsorption energy of HgSe on the surface of PbSO₄ blocks, thus strengthening the pyrolysis process of HgSe and reducing energy consumption. The preferable prototyping technology for resource utilization of toxic acid mud should be microwave roasting. This study is of great significance for the realization of mercury pollution reduction and for green production of lead-zinc smelting.