IMPROVEMENT OF CYANIDATION AT NEW BRITANNIA MINE

摘要

The New Britannia Mine processes a quartz-carbonate gold ore containing 4.63 g/t Au at a rate of 2,200 tpd. The ore contains approximately 3.0 percent arsenopyrite, 2.7 percent pyrite and the rest is gangue minerals. Eight to ten percent of the gold is refractory to leaching. Two years ago, New Britannia Mine experienced cyanidation problems. Gold extraction was not stable and occasionally decreased significantly. Preliminary test work, at laboratory scale and in the plant, indicated that lead nitrate addition was beneficial. A laboratory study was initiated to evaluate the level of control of the parameters (grinding size, dissolved oxygen, pH, free cyanide and lead nitrate) to optimize the efficiency of the process. It was found that lead nitrate addition is required to alleviate the effect of metallic sulphides. This addition causes a significant increase in the gold leaching kinetics and a reduction in the cyanide consumption. The optimum system appeared to be: leaching for 24-30 hours at pH 11.8, 50 g/t lead nitrate, 250 ppm NaCN and 8 ppm O_2. The gold extraction was 89.8 percent with grinding at 89 percent-74Fm (leached tail at 0.48 g/t). Cyanide and lime consumption are 0.40 kg/t NaCN and 1.9 kg/t respectively. Following the incorporation of lead nitrate, overall gold extraction was increased from 89.2 percent to 91.1 percent but no change was noticed in cyanide consumption. The gross profit is