The effect of Pb(NO3)2 addition on the processing of blended Fort Knox and True North ores at the Fort Knox mine, Alaska

Abstract

Fairbanks Gold Mining Inc. (FGMI) began blending and processing True North ore at its Fort Knox mill on April 12, 2001. Gold extraction subsequently dropped from 88% to 71% during the last week of April 2001. Twenty-five percent of the gold values remaining in the leach tailings were gravity-recoverable free gold. Significant quantities of stibnite and arsenopyrite were also identified in the tailings. In laboratory bottle-roll tests, the gold extraction from a composite of leach circuit feed collected during the same period was 72.6% when leached at an average NaCN concentration ofO. 16g/kg. The extraction increased to 82.4% with 0.5 g/kg NaCN and increased to 91.7% with 0.5 g/kg NaCN plus 0.075 g/kg Pb(NO3)2. A passivating layer, resulting from sulfide mineral dissolution, surrounded the liberated gold particles and likely contributed to the reduced gold recovery. The gold recovery can be substantially increased by the addition of lead nitrate. Lead species remain in the solid residues after leaching and were not mobilized using meteoric water mobility procedure.