Germanium (Ge) is one of the critical elements of modern technologies, with supply risk, inefficient production, and increased demand. It is used in high technology applications such as infrared systems, fiber optics, polymer catalysis, electronics, and solar cells. Its demand is expected to increase due to lack of suitable substitutes, increasing demand for solar cells and 5G networks, and the continuous increasing trend of Ge demand for the past 20 years. Globally, 130 tonnes (t) of Ge are being produced (2020) primarily in China. Germanium is recovered as a byproduct from Zn-refineries and coal fly ash. Yet very low amount (<3%) of Ge contained in Zn-ores and fly ash is recovered worldwide, which suggests that the criticality of Ge is due to lack of economical and efficient extraction and recovery process rather than lack of resources. Worldwide, it is estimated that Zn-ores contain 7–13 kt Ge, and coal and coal fly ash, 25–112 kt. The production of Ge involves leaching followed by recovery of Ge by chlorination-distillation, precipitation, solvent extraction, ion flotation, supported liquid membranes, ion exchange, or solid-phase extraction. Leaching from Zn-refinery residues is primarily done with mineral acids, whereas from coal fly ash is achieved with organic ligands. Ge is different from common metal cations, as it exists as neutral species in acidic pH (1–7). Thus, organic ligands are used to form anionic germanium-ligand complexes in solvent extraction and ion-exchange processes so that the species can be separated through anion-exchange. Alternatively, chelating solvent extractants, chelating ion-exchange resins, and ligand functionalized adsorbents in solid-phase extraction (SPE) are used to recover Ge. The primary challenges in Ge hydrometallurgical production are high energy and chemical requirements in precipitation/chlorination-distillation, high chemical consumption, impurities co-extraction, and waste stream generation in solvent extraction, and lack of selective and high-capacity adsorbents in SPE. An improved, efficient, and economical production method, utilizing unconventional resources, can reduce Ge supply risk. SPE has various advantages over other processes, which makes it an attractive option to recover Ge efficiently and economically.
All Science Journal Classification (ASJC) codes
- Analytical Chemistry
- Filtration and Separation