Gold recovery optimization of a refractory concentrate by ultrafine grinding – a laboratory study

Minerals & Metallurgical Processing , 2011, Vol. 28, No. 2, pp. 94-101

González-Anaya, J.A.; Nava-Alonso, F.; Pecina-Treviño, E.T.

ABSTRACT:

This laboratory work presents a study of the effect of ultrafine grinding on the gold recovery of a highly refractory gold concentrate. The particle size of the concentrate was P₈₀ = 46 μm and the main species present were quartz (28.58%), dolomite (25.63%), pyrite (20.93%), arsenopyrite (15.39%) and 112 g/t gold. After optimizing hydrated lime and lead nitrate additions, standard cyanidation with 1% NaCN, pH = 12.3, 25% S/L permits to recover only 9.4% of the gold. Different particle sizes were submitted to cyanidation. When the concentrate was ground to ultrafine sizes (P₈₀= 4.6 μm), the gold recovery for the same cyanidation conditions increased to 67%, with cyanide consumption of 66.7 kg NaCN/t. Additional tests were performed in order to reduce the cyanide consumption. The reduction of the cyanide concentration in the leaching solution from 1 to 0.5% and the addition of 100 g Pb(NO₃)₂/t allowed the reduction of the cyanide consumption to 27.6 kg NaCN/t (58% reduction), while maintaining the same gold recovery of 67%. The remaining gold could be present as very fine inclusions or in solid solution in the matrix.