Alternative Technologies to Mercury in Gold Processing: A Review of Challenges and Perspectives

Artisanal and small-scale gold mining (ASGM) is present in more than 80 countries and involves approximately 15 million miners. This sector is recognized as one of the main global sources of mercury emissions. The Minamata Convention on Mercury aims to reduce and, where possible, eliminate mercury use in ASGM; however, the total amount of mercury used worldwide remains uncertain. This literature review aims to identify and critically discuss mercury-free or mercury-reducing technologies for gold recovery reported between 2013 and 2023. The Scopus database was used, applying a 10-year publication filter, and 50 articles were selected. The technologies were classified into four metallurgical routes: hydrometallurgy, physical metallurgy, biometallurgy, and pyrometallurgy. The review indicates that mercury replacement cannot be achieved through a single universal technology. For informal ASGM operations treating alluvial or free-milling ores containing free or sufficiently liberated gold, the most plausible mercury-free pathway is improved gravity concentration to produce gold-rich concentrates for sale or controlled downstream treatment. Physical methods should therefore be understood as concentration or upgrading steps rather than direct gold extraction technologies. Flotation, cyanidation, alternative lixiviants, borax-assisted smelting, and biometallurgical approaches may be relevant under specific mineralogical, operational, and institutional conditions, but they require different levels of technical control, environmental safeguards, and process management. Therefore, efforts to reduce mercury use in ASGM should prioritize ore-specific processing routes, technical assistance, environmental safeguards, and local feasibility rather than relying only on theoretical recovery potential.