Kibali Gold Mine Ultrafine Grinding Circuit: Case Study from commissioning to optimized operation


Thamsanqa Mahlangu, Randgold Resources, Kibali Gold Mine; Craig Brickhill, FLSmidth (Pty) Ltd; Guy Ngombe Kalenga, Kibhali Gold Mines; Byron Sirchia, FLSmidth South Africa, Process Department; Beddy Mukonkole Sindani, Kibali Gold Mine; Patrick Mande, Kibali Gold Mine; Gustav Du Toit, Kibali Gold Mine

With ore reserves becoming more complex and finely disseminated, ultrafine grinding mills are becoming more common in metallurgical plants. Important applications of stirred mills are to improve the recovery of valuable metals such as gold into and/or from flotation concentrates.  Kibali gold mine gold processing plant recovers gold from the primary circuit into a flotation concentrates with a mass pull ranging between 10 and 15%.  The flotation concentrate, is subjected to ultrafine grinding in eight (8) parallel FLS VXP 2500 mills and subsequently undergoes a two-stage pre-oxidation process at controlled pH, prior to cyanide addition.  The plant was commissioned in 2014 with an initial installation of four (4) mills. Four (4) more mills were added as the operation moved from a dual oxide – sulphide circuit to a twin sulphide full flotation operation.  This was consistent with an almost 100% increase in the flotation concentrate tonnes being treated in the circuit from 1500 to 2700tpd.   Various optimisation test-campaigns have been conducted since the mills were first installed with the aim of optimising mill performance, and thus subsequent dissolution efficiencies downstream in the cyanide leach process.  Key mill performance indicator, primarily specific energy consumption to achieve the specified grind of between 15 and 22microns, was studied by running various tests at different levels and combinations of the following parameters: •           media filling •           mill rotational speeds •           feed slurry flowrate •           grinding assembly configuration •           media density •           grinding assembly configuration (tested in 2016/7 – more results available?)   Based on the testwork results, optimum operating parameters were established. A financial analysis was also conducted to estimate the impact of VXP product grind on plant economics. This paper provides details of the testwork and financial analysis conducted on these mills.
Keywords: Kibali Gold Mines, Ultrafine Grinding, Flotation gold Concentrates, optimisation, VXP mills