A study of thiosulfate leaching of gold from carbonaceous ore and the quantitative determination of thiosulfate in the leached solution

Abstract

The objective of this study was to investigate leaching of gold from carbonaceous ore using ammoniacal thiosulfate solutions, and to determine the consumption of thiosulfate during leaching. The quantitative determination of thiosulfate in the leached solution in the presence of sulfite and sulfate ions was accomplished by means of flow injection analysis with electrochemical detection. Lower thiosulfate consumption, which is an indication of solution stabilization, was achieved by addition of sulfite and maintenance of the solution at a pH of 10. 5. Decomposition of thiosulfate was found to be g r eater at high temperatures. The optimum conditions for extraction of gold were found to be pH of 10.5, and temperature of 35°C. At these optimum conditions, 73 percent gold extraction was obtained. It was also shown that thiosulfate will leach gold from oxide ores but not as effectively as cyanide. While a high percent extraction of gold was obtained from the carbonaceous ore, poor recovery of gold was observed from the sulfide ore, which is also a refractory ore as is the carbonaceous ore. A comparison of thiosulfate with cyanide leaching of gold from carbonaceous ore showed that thiosulfate is chemically better and economically more advantageous.