The recovery of gold from refractory arsenopyrite concentrates by pyrolysis-oxidation

A gold bearing arsenopyrite concentrate was characterised, and found to consist of 70% arsenopyrite and 25% pyrite with a small amount of stibnite and silicate minerals. On cyanide leaching only 6% of gold was extracted. Of the remainder, the gold associated with the arsenopyrite fraction was in solid solution, as was some of the gold in the pyrite fraction. When samples were pyrolysed in nitrogen or carbon dioxide, so that the pyrite and arsenopyrite were decomposed to pyrrhotite, and cyanide leached, recoveries improved to between 40–50%. Microscopic examination of the leached panicles indicated that the gold was encapsulated in the pyrrhotite, and therefore still inaccessible to the leaching reagents. When fresh samples were pyrolysed at 700°C for 30 minutes, and then oxidised for two hours in pure oxygen at 550°C and cyanide leached, the gold recovery increased to 97%. As the oxidation temperature increased to 650°C the gold recovery decreased to 78%. In air, a maximum recovery of 86% was obtained at a roasting temperature of 550°C for 6 hours.