Optimisation of biooxidation nutrients for enhanced gold recovery: A case Study at Golden Star Bogoso/Prestea Limited

Abstract

With growing interest in the development of novel technologies for the treatment of refractory gold deposits, the biological oxidation process has gained wide range acceptance due to its relatively lower operating cost and environmental friendliness. However, with the downward plunge in gold prices in recent years, the profitability of using this process is questionable and for Golden Star Resources, the mine under study, the Biological Oxidation (BIOX) Plant is under care and maintenance because the cost of production outperformed the sale of products. In an effort to reduce the operating cost further to make this process an economically viable option, a nutrient optimisation study was undertaken, which is the main objective of this work. Chemical and mineralogical characterisation of flotation concentrate revealed average sulphide sulphur and organic carbon contents of 13.83% and 2.91% respectively, and a gold grade of 39.47 g/t. Acid leaching of the flotation concentrate for a 5 day residence time revealed that, 0.362 kg/t nitrogen (N), 0.702 kg/t phosphorus (P) and 0.417 kg/t potassium (K) could be made bio-available in the process stream. Sulphide sulphur oxidation was conducted using varying percentages of NPK relative to the Genmin standard of 1.7:0.3:0.9 kg/t of NPK, after which the products were subjected to gold leaching by cyanidation. For no nutrient addition (0% Genmin standard NPK), 46% sulphur oxidation (SOX) was achieved, whereas 100% addition 95.2% sulphur oxidation. The corresponding gold recoveries were about 73.9% and 95.7% respectively. Various SOX ranging between 41.1% and 95.7% were obtained for the different dropwise reductions in NPK, and subsequent cyanidation gave recoveries between 55.7% and 97.7%. The highest gold recovery of 97.7% was recorded after the flotation concentrate was oxidised with 0.58:0.30:0.90 kg/t of NPK to obtain a SOX of 91.2%. This thesis contributes greatly to knowledge as the results obtained set a platform for deeper research into reduced processing cost based on the optimisation of BIOX nutrients