A review of biocyanidation as a sustainable route for gold recovery from primary and secondary low-grade resources

Gold recovery from limited global resources has gained increasing attention due to a growing demand for gold and heightened social awareness of the high toxicity and the environmental threat of traditional cyanidation. This has led to the development of biomining methods to extract gold from low-grade ores and a variety of wastes using microbes to generate the required reagents. One such method, biocyanidation, has the potential to be an environmentally friendly technique for gold recovery from ore and secondary resources. This review quantifies the limited global gold resources, presents the gold leaching technologies, and describes the biocyanidation process, including the properties of commonly used cyanogenic bacteria and the influencing factors. Methods to measure free biogenic cyanide are summarized, with a focus on the silver nitrate method with potentiometric end-point titration. Finally, biocyanidation is systematically and comprehensively analyzed in the context of commercial and technical limitations imposed by low-grade gold reserves that are infeasible for commercialization, and recommendations for improvements to the process are suggested. This review provides insights on the necessity and urgency of recycling gold from both primary and secondary resources, the crucial role of biocyanidation, the present challenges and future directions toward commercial application of the process.