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
