The Influence of Integrated Gravity Circuit on Efficiency of Gold Extraction at a Carbon-in-Leach Plant

Abstract

In gold ores, the precious metal particles may occur as nuggets (> 0.5 mm) and down to sub-microscopic particles. Coarse particles are generally recovered by gravity concentration before leaching of the bulk material with sodium cyanide. A mine in West Africa operates a Carbon-In-Leach plant where a gravity circuit has recently been installed. Purpose of this study was to investigate the effect of gravity circuit on efficiency of metallurgical operations in the processing plant. A quantitative research was selected to determine the variables in analysing the influence of integrated gravity circuit on the efficiency of gold extraction. The plant efficiencies before and after the installation of the Gravity Recoverable Gold (GRG) circuit were investigated, focusing on the milling, CIL, and reagent consumption in the various circuits. Using multiple linear regression, a model was constructed and the relationship between variables was determined. From the results, mill's throughput increased from 13.5 million tonnes to 13.9 million tonnes per year after the installation of the GRG circuit. In models 1 and 2, all p-values were less than the 5% significance level chosen for the study. Cost-benefit analysis of reagent use before and after gravity installation showed that plant consumption of reagents decreased from 43 264 – 36 481 tonnes, 13 144 – 10 141 tonnes, 1 779 – 1 538 tonnes, 3 208 – 1 551 tonnes, 9 274 – 8 045 tonnes for lime, sodium cyanide, activated carbon, hydrochloric acid and caustic soda respectively. GRG circuit dramatically reduced the gold in tailings and increase gold recovery rate and purity by 1% and 2% respectively. Overall, the mine's annual ore processing capacity increased by 2.34 %. Installation of additional Knelson concentrators can be key to addressing the excess gravity-recoverable gold suspected to exist in the circuit with continuous checks and balances performed