Thiosulfate-copper-ammonia leaching of pure gold and pressure oxidized concentrate
1
Aalto University, School of Chemical Technology, Department of Materials Science and Engineering
2
VTT Technical Research Centre of Finland
Publication date: 2017-05-10
Corresponding author
Antti Porvali
Aalto University, School of Chemical Technology, Department of Materials Science and Engineering, Vuorimiehentie 2, 02150 Espoo, Finland
Aalto University, School of Chemical Technology, Department of Materials Science and Engineering, Vuorimiehentie 2, 02150 Espoo, Finland
Physicochem. Probl. Miner. Process. 2017;53(2):1079-1091
KEYWORDS
TOPICS
ABSTRACT
In this research cyanide-free leaching of pure gold and pressure oxidized refractory gold concentrate by thiosulfate-copper-ammonia solutions were examined. A quartz crystal microbalance (QCM) was used to study gold leaching as a factorial series where the best gold leaching rate (2.987 mg/(cm2∙h)) was achieved with a solution consisting of 0.2 M (NH4)2S2O3, 1.2 M NH3, 0.01 M CuSO4 and 0.4 M Na2SO4. Temperature had the greatest effect on the gold leaching rate. An increase in thiosulfate concentration (0.1–0.2 M) increased gold dissolution. The combined effect of temperature and ammonia concentration had a statistically significant effect on the gold leaching rate at 0.1 M M2S2O3. Combination of applied potential and NH3:S2O3 ratio had a statistically significant effect on the gold leaching rate at 0.2 M M2S2O3. An increase in applied potential decreased the gold dissolution rate at low ammonia concentrations but increased it at high concentrations. A pressure oxidized gold concentrate was leached for 6 hours in the batch reactor leaching experiments. The effect of rotative velocity (1.26–1.56 m/s) and slurry density (10–30 wt%) was investigated at the following leaching parameters: 0.2 M Na2S2O3, 0.6 M NH3, 0.01 M CuSO4, 0.4 M Na2SO4. Lower slurry density (10 wt%) resulted in a higher Au leaching efficiency. An increase in the rotation rate did not have an effect on the final Au leaching recovery. The best Au leaching efficiency (89%) was achieved with 590 rpm mixing, 1.56 m/s rotative velocity and 10 wt% slurry density.
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