Germanium: A review of its US demand, uses, resources, chemistry, and separation technologies

•Efficient and economic production process can mitigate criticality of germanium.•US germanium resources remain unused due to inefficiency in production.•Production processes including leaching, precipitation, and separation are reviewed.•Separation includes precipitation, solvent-extraction, ion-exchange, and adsorption.•Ge chemistry differs from other cations as it remains as neutral species in acidic pH. 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 (