PYROLYSIS OF ARSENOPYRITE FOR GOLD RECOVERY BY CYANIDATION

Gold in arsenopyrite or high-arsenic pyrites commonly exists as submic roscopic or ''invisible'' inclusions, making it refractory to cyanide leaching. Current practice favour an oxidising roast to liberate the g old for cyanidation because it is fast and energetically self supporti ng, However the SO2 gas it produces can create a handling problem. One alternative we are investigating is pyrolysis under N-2, CO2 and SO2 atmospheres. Instead of gaseous SO2, the process produces elemental su lfur and, if present in the ore, arsenic metal or solid arsenic oxide. Pyrolysis experiments were conducted on a gold-containing refractory arsenopyrite ore to determine the effect of temperature, time and atmo sphere on the cyanidation characteristics of the pyrolysis product. In N-2 and CO2, the ore behaved similarly, reaching maximum mass loss at 700 degrees C and yielding maximum gold recoveries of 35 and 48 %, re spectively. Pyrolysis under SO2 was faster reaching maximum mass loss at 600 degrees C and resulting in gold recoveries of up to 61%. The lo w gold recovery for N-2 and CO2 pyrolysed products was due to the enca psulation of the exsolved gold particles by pyrrhotite as it recrystal lised during the process. All the pyrolysis products, although compose d mainly of pyrrhotite, did not seem to be highly active in cyanide so lutions.