Articles

Germanium Processing from Primary and Secondary Resources: Occurrence, Extraction Technologies, and Circular Economy Perspectives

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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.

Phytomining as an Emerging Metal Recovery Route: A Critical Review of Plant Uptake Mechanisms, Processing Strategies, And Industrial Constraints (2020–2025)

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Phytomining has re-emerged as a promising strategy for the sustainable recovery of valuable and critical metals from soils, mine tailings, and industrial residues, while simultaneously contributing to environmental remediation. This critical review synthesizes advances published between 2020 and 2025, focusing on the biological, agronomic, and metallurgical foundations that govern phytomining performance and scalability. Recent progress in hyperaccumulator selection, soil amendments, plant–microbe interactions, and biomass processing has expanded the range of target metals beyond nickel to include gold, platinum-group metals, rare-earth elements, and scandium. However, field-scale deployment remains constrained by trade-offs between biomass productivity and metal concentration, as well as by the efficiency and cost of downstream ash processing and metal recovery. By integrating reported case studies, techno-economic assessments, and environmental indicators, this review positions phytomining within circular economy and nature-based remediation frameworks. Key knowledge gaps have been identified in process integration, quantitative performance metrics, and long-term sustainability, providing a roadmap for transitioning phytomining from experimental trials to industrially relevant applications.