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.

Preg-Robbing in Refractory Gold Ores: A Critical Review of Mineralogical Controls, Pretreatment Strategies and Flowsheet Selection

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Preg-robbing remains a major constraint in the processing of refractory gold ores, particularly those containing carbonaceous matter, fine clays, and iron-bearing phases capable of adsorbing dissolved gold during leaching. This review critically evaluates advances reported between 2020 and 2025, focusing on the mineralogical controls of preg-robbing, its interaction with gold dissolution chemistry, and the effectiveness of current mitigation strategies. Gold adsorption is governed by carbon structure, surface functional groups, sulfide associations, and textural features that control accessibility, determining whether adsorption is reversible or irreversible and, consequently, whether conventional recovery routes remain viable. Pretreatment options, including roasting, pressure oxidation, bio-oxidation, chemical passivation, and selective removal of reactive phases, are assessed in terms of metallurgical performance, operational complexity, energy demand, and environmental impact. The review also examines alternative lixiviants such as thiosulfate, glycine, and ammonia-based systems, highlighting their potential to reduce sensitivity to carbonaceous matter while emphasizing their dependence on mineralogy and process control. Rather than proposing a universal solution, the analysis defines decision-oriented criteria for flowsheet selection based on mineralogical and operational constraints, identifying the conditions under which specific approaches are technically robust and economically justified. Key research gaps are highlighted, particularly in the quantitative characterization of adsorption capacity and kinetics, and in the integration of mineralogical data into predictive process design frameworks.

Physicochemical and radioactive study of Colombontatalite ore from the Kisengo quarry in the DRC

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This research concerns the assessment of radioactivity and the physicochemical characterization of columbotantalite ore extracted from the Kisengo quarry, located in the Tanganyika province of the Democratic Republic of Congo. The sample was taken from the Kisengo open-pit mine in Nyunzu territory located about 170 km from the town of Kalemie in Tanganyika province/DRC. It contained about 32% niobium, 21% tantalum, 6% iron, 7% manganese, 7% tin, 4% silicon and about 3% titanium and was analyzed by XRF. The results of the radioactivity tests revealed that the average dose rate, measured in nGy/h, was 329.72, or 0.038 mSv with the Identifinder device. This sample does not pose a risk of radioactive exposure, as the dose levels are very low, in accordance with the WHO range of 20 mSv and DRC Law 017/2002. Analysis of optical microscopy images of Kisengo coltan reveals the presence of a siliceous gangue (quartz) associated with pyroxenes as well as columbotantalite, which is the mineral of tantalum and niobium. Also present are cassiterite, a tin mineral (SnO2), and pyrolusite, a manganese mineral (MnO2). Granulochemical characterization revealed that tantalum and niobium are concentrated in the 500 micrometer fraction. The loss on ignition test indicated that niobium is the most abundant element in the analyzed sample, representing 31.97%, followed by tantalum at 20.75%. Finally, silicon and titanium are present and removed at 4.18% and 17.716%, respectively.