Recovery of Gold from Refractory Sulphide Concentrates by Means of Pressure Oxidation and Thiocyanate Leaching

Abstract

The alternative method for gold recovery from POX cakes is thiocyanate leaching. This method has several advantages: thiocyanate is less toxic than cyanide; complex [Au(SCN)4]– is very stable (lgβ = 43.9); leaching of gold is carried out in sulfate media without CCD and neutralization of acidic POX slurry; high rate of this process; the gold oxidant is ferric ions which formed during POX of iron sulfides. The test work on pressure oxidation and thiocyanate leaching was carried out for refractory sulfide gold-copper flotation concentrate. The gold content in the concentrate was 31.8 g/t. Pressure oxidation tests at the temperature of 220 oC and the oxygen pressure of 0.7 MPa were carried out. The POX slurry to 90–95 oC was cooled and thiocyanate leaching of gold was carried out at atmospheric pressure. The concentration of thiocyanate ions was changed from 0.5 to 2 g/dm3. The recovery of gold from leaching solution was carried out by activated carbon. The loaded carbon to cyanide treatment, thermal reactivation and acidic treatment for copper and iron remove was subjected. The cyanide treatment was carried out with a sodium cyanide solution of 20 g/dm3. Thermal treatment was carried out at the temperature of 650–700 oC for 0.5 h. The acidic treatment was carried out with a hydrochloric acid solution of 20 g/dm3. After impurities removing the carbon in next experiments was used. 6 cycles gold adsorption and carbon regeneration were carried out. It was shown that thiocyanate gold leaching from POX products can be carried out in the CIP and CIL modes. Gold recovery was over 95%. 80–99% of copper, 65–88% of iron and 90–99% of sulfur were recovered from carbon during removing cycles. The gold adsorption process in each cycle had line nature. The content of gold in the loaded carbon after six cycles was 0.5 kg/t, and after long time CIP process was 3.9 kg/t. The gold stripping by alkaline solution was 97%. The gold content in the stripped carbon was 0.016 kg/t. The copper and iron content was 0.021 and 0.132 kg/t, respectively.