Leaching Gold and Silver with an Alternative System, Glycine: Thiosulfate from Mineral Tailings

An alternative system to cyanide as a leaching agent is presented for the recovery of gold and silver from cyanicide minerals. These minerals are characterized by the presence of copper and carbonaceous minerals in their composition, therefore increasing both the consumption of reagents and energy requirements for the detoxification and destruction of cyanide. The characterization was carried out with a mesh of + 80 to − 325; gold and silver were determined by a fire assay. The determination of mineralogic species was made by scanning electron microscopy and x-ray diffraction. Thiosulfate and glycine are environmentally friendly agents because of their low toxicity and easy degradation; both agents can form stable complexes with gold and silver in a basic media. These features were studied for the treatment of mine tailings from a Mexican mine. Both systems were evaluated by 48-h leaching tests at different liquid–solid ratios (in the range of 1:1, 2:1 and 3:1) and showed significant recoveries of gold, > 80%, with thiosulfate as well as considerable consumption of thiosulfate. These consumptions were, however, lower with the presence of glycine in the system. The recovery of gold and silver through the non-ammoniacal thiosulfate system adds an important step in the development of a sustainable mining process.