Initial loss of cyanide, thiocyanate, and thiosulfate adjuvants following amendment to an oxidic gold ore

Gold extraction and gold phytomining involve the use of adjuvants such as cyanide, thiocyanate, or thiosulfate to facilitate the dissolution of gold and its subsequent recovery. The adjuvants can be applied at high rates, in excess of 1 kg t⁻¹ for some ores. At these concentrations, concerns have been expressed about adjuvant persistence and associated detrimental repercussions for the environment. The incubation study here examined the initial disappearance of these adjuvants in the dark following their amendment at 1 g kg⁻¹ gold ore. Over a 24 d period, nearly 75% of the initial thiocyanate was lost within 24 d while >50% of thiosulfate and cyanide was lost over the same time frame. Cyanide and thiosulfate loss showed an exponential loss while thiocyanate was observed to follow a biphasic relationship. For the oxidic ore used, the adjuvants were not inherently persistent, suggesting that natural attenuation may rapidly promote adjuvant loss under specific conditions.