Abstract : Germanium is a critical technology metal used in fiber optics, infrared optics, photovoltaics, semiconductors, and emerging energy systems. Despite its strategic importance, primary germanium resources are limited, and global production remains heavily dependent on by-product recovery from zinc processing, coal fly ash, and copper-related residues. This review critically examines the occurrence, mineralogy, and distribution of germanium in both primary and secondary resources, emphasizing the growing importance of urban mining and industrial waste valorization. Current recovery technologies are analyzed, including pyrometallurgical, hydrometallurgical, chlorination, volatilization, solvent extraction, ion exchange, and biohydrometallurgical routes. Particular attention is given to the efficiency of selective separation, impurity behavior, energy demand, environmental constraints, process integration, and scale-up limitations. The review highlights that germanium dissolution is often less challenging than downstream purification and selective recovery from chemically complex, highly dilute process streams. Major technological barriers include ultra-low Ge concentrations, impurity-rich matrices, solvent degradation, reagent consumption, and the limited industrial maturity of several emerging recovery technologies. Recent advances in secondary recovery from electronic waste, coal-derived residues, and metallurgical by-products are critically evaluated within the broader context of circular economy strategies and integrated multi-metal recovery systems. The analysis indicates that future germanium supply will depend less on primary mining expansion and more on the ability to selectively recover Ge from complex secondary resources through integrated, economically robust processing systems.
Pereira Antonio Clareti (Fri,) studied this question.