Comparative Characteristics of Gold Extraction Methods (Cyanide, Thiosulfate, Thiourea, Chloride)

This paper presents a comparative assessment of four hydrometallurgical routes for gold recovery–cyanide, thiosulfate, thiourea, and chloride–benchmarked by extraction efficiency, toxicity, costs, and waste management requirements. Mineralogical constraints (refractoriness, carbonaceous matter, sulfide locking) are highlighted to show that solvent selection must consider not only final extraction levels but also dissolution rate, impurity sensitivity, and the need for pre-treatment. Typical performance windows are summarized: 90–95 % for amenable ores under cyanidation; comparable results for thiosulfate and thiourea flowsheets on carbonaceous and stibnite-rich feeds; and high recoveries for chloride systems when redox and acidity are tightly controlled. Direct reagent costs are generally lowest for cyanide because of low dosage and mature equipment, whereas thiosulfate demands higher make-up and specific regeneration; thiourea and chlorine-bearing reagents increase effluent treatment costs and materials requirements. Detox and cleanup blocks are outlined: SO2 / air (INCO) for cyanide, precipitation and biodestruction for ammoniacal thiosulfate, oxidative destruction and neutralization for thiourea, and gas/liquid treatment with salt balance for chloride circuits. Hybrid routes (gravity/ flotation + leaching) help tailor the process to ore type while controlling environmental risk and unit cost.