The Influence of Integrated Gravity Circuit on the 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 the bulk material with sodium cyanide to enhance leaching efficiency. A mine in West Africa operates a carbon-in-leach (CIL) plant where a gravity circuit has recently been installed. The purpose of this study was to investigate the effect of the gravity-integrated circuit on the overall efficiency of metallurgical operations in the CIL plant. In this investigation, a quantitative research approach was selected to determine the variables in analysing the influence of the integrated gravity circuit on the efficiency of gold extraction. The general plant efficiencies before and after the installation of the Gravity Recoverable Gold (GRG) circuit were investigated, with a focus on the milling circuit, CIL circuit, and reagent consumption in the various circuits. A model was constructed using multiple linear regression analysis, and the relationship between the variables was determined. From the results, the mill's throughput increased from 13.5 million tonnes per year to 13.9 million tonnes per year after the installation of the GRG circuit. In models 1 and 2, all coefficient 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 the 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. Again, the GRG circuit dramatically reduced the gold loadings onto activated carbon with an overall reduction in tailing grade and increased the gold recovery rate and purity by 1% and 2%, respectively. Overall, the mine's annual ore processing capacity increased by 2.34 %. Therefore, installing additional Knelson concentrators (gravity units) can be key to addressing the excess gravity-recoverable gold suspected to exist in the circuit with continuous checks and balances performed.