Abstract
Gold ore grades are declining, refractory mineralization is increasing, and electronic scrap and copper anode slime have reached industrial volumes. For such feeds the rate-limiting stage is selective separation from a chemically loaded matrix, whereas dissolution chemistry is established. This review compares cyanide, thiosulfate, thiourea, thiocyanate, halide, glycine and enhanced-oxidation systems by transferability between primary and secondary feeds. Cyanidation remains the benchmark, but its margin narrows once copper consumption, encapsulation and detoxification costs are counted. Each alternative lifts one restriction and imposes others on reagent stability and selectivity. Progress depends on integrating dissolution, separation and effluent management for heterogeneous feeds.