Abstract
Germanium, a critical material for advanced technologies, is enriched in certain coal deposits and by-products, including coal combustion and gasification fly ashes. This review examines germanium concentrations and occurrence modes in coal, coal gangue, and their combustion or gasification by-products, as well as hydrometallurgical recovery methods at laboratory, pilot, and industrial scales. Fly ashes from both coal combustion and gasification are particularly promising due to their higher germanium content and recovery rates, which can exceed 90% under optimal conditions. However, the low germanium concentrations and high levels of impurities in the leachates pose challenges, necessitating the development of innovative and selective separation techniques, primarily involving solvent extraction, ion exchange, or adsorption.