PROCESSING OF HIGH SILVER-GOLD ORES WITH GLYCAT~(TM) TECHNOLOGY

摘要

Gold and silver are traditionally extracted from high silver-gold ores by cyanidation with high concentrations of cyanide in both the leaching and Merrill-Crowe metal recovery steps. Cyanide is continually consumed during the cyanidation process and additional cyanide needs to be added in order to maintain cyanide levels at the optimum leaching concentration. This paper investigates an alternative gold and silver extraction process, consisting of a cyanide-catalysed glycine leaching system, known commercially as GlyCat~(TM). The silver-gold ore used in this study contained 3.13 g/t gold and 64 g/t silver. The gold was predominantly present as native gold and the silver predominantly present as silver halides. The leaching conditions for the GlyCat~(TM) system were glycine at 7.5 g/L, ferricyanide at 1.5 g/L, with the sodium cyanide (NaCN) concentration maintained at 200 ppm for the duration of the test. Cyanidation leaching was undertaken with NaCN maintained at concentrations of 1000 ppm for the duration of the test. A level of 1000 ppm cyanidation was adopted for this study as it represents a level that would typically be employed industrially for this type of ore. The leaching rate in the GlyCat? system was found to be approximately tenfold faster than the 1000 ppm cyanidation system, with higher gold recovery after 6 hours at 98% for the GlyCat? system. Gold and silver recovery from cyanidation leaching at 1000 ppm after 48 hours were 97.1% and 80% respectively, compared to 96.7% and 75.6% respectively for the GlyCat~(TM) system for the same time period. Gold and silver recovery from cyanidation leaching at 200 ppm after 48 hours was much lower at 85.5% and 52.0% respectively. In the GlyCat~(TM) system, 0.81 kg/t of NaCN was consumed compared with 2 kg/t in the 1000 ppm cyanidation system. Lime consumption was also lower for the GlyCat~(TM) system, with 2.82 kg/t lime consumed compared to 4.3 kg/t lime for the 1000 ppm cyanidation system. Lower mercury dissolution was observed in the GlyCat~(TM) system, with 0.7% dissolved into solution, compared to 10% during the cyanidation at 1000 ppm. The concentration of free cyanide present in the final leach solution for the GlyCat~(TM) process was 175 mg/L, which was approximately 20% of the free cyanide present in the final leach from the 1000 ppm cyanidation process. The results showed that the GlyCat~(TM) leaching system achieved a similar level of gold and silver metal recovery to cyanidation at 1000 ppm, but with reduced cyanide consumption, reduced lime consumption and reduced mercury dissolution compared to the cyanidation system. Cyanidation at 200 ppm achieved significantly lower gold and silver recoveries compared to the GlyCat~(TM) leaching system.