Leaching of gold and silver from a Kupol composite sample: assessment of the CANMET enhanced leaching process (CELP)

In an earlier study (Deschênes et al., 2009), gold and silver were shown to be efficiently extracted from samples taken from the Kupol Mine in Russia using lead nitrate in a cyanide leach system. In the current study, we compared the technical and economic merits of a novel technology known as CANMET enhanced leaching process (CELP) with the conventional cyanidation/acidification-volatilization-recycling (AVR) process by utilizing eight metallurgical variability samples along with a representative large composite sample representing the first two years of mill feed from the Kupol site. The composite sample exhibited assays of 33.4 g/t Au and 289 g/t Ag. Metallurgical findings indicated that CELP yielded comparable gold extractions and slightly higher silver extractions than cyanidation/AVR under half the cyanide concentration utilized in the conventional method (1,000 ppm NaCN in CELP versus 2,000 ppm in cyanidation/AVR). Total costs per ton for both processes were found to be approximately equal, although implementing CELP would negate a capital expenditure of about $5 million required for the AVR system. Further evaluations on variability samples confirmed CELP's effectiveness, which led to the decision to adopt CELP at Kupol, thus allowing the use of conventional leach equipment and streamlining the flowsheet due to the remote operations of the mine.