African Eagle has chosen to employ straightforward and proven atmospheric acid leach in agitated tanks to dissolve the ores (with the addition of sulphuric acid) and recover the nickel, otherwise known as atmospheric tank leaching (“ATL”). ATL is a well proven technology for processing other metals, such as cobalt, copper and gold, and uses standard processes and equipment.
This follows a comprehensive metallurgical test work campaign that demonstrated that the Dutwa principal ores were amenable to ATL and that this process was more favourable to the overall project economics and operating environment, and possesses a lower risk profile than either high pressure acid leach (“HPAL”) or heap leaching.
Unlike many other nickel laterites, it is the low iron and high silica content that enables the Dutwa ores to be amenable to leaching at atmospheric pressure as there is less that needs to be leached and subsequently removed from solution when it is purified prior to producing the concentrate. The silica remains essentially inert and does not react with the acid at atmospheric pressure, lowering the overall acid consumption. The Dutwa “FeSi” ores also have a low (2-3%) magnesium content, which further reduces their acid demand.
ATL is reportedly achieving recent success at the Ravensthorpe mine, owned & operated by First Quantum in Western Australia. First Quantum released information in the first quarter 2012 on the Ravensthorpe’s operation, which showed the ATL plant performing above design capacity after being brought back into operation as recently as the fourth quarter 2011. It is important to note that the problems Ravensthorpe experienced when previously owned by BHP Billiton were not related to the ATL plant. It is also under consideration for use at Weda Bay, Eramet’s project in Indonesia.
African Eagle’s pilot plant test work campaign will be conducted at the same laboratory, SGS Lakefield Oretest in Perth (Western Australia) and in the same pilot plant that was used for the Ravensthorpe test work. First Quantum’s success with the ATL plant confirms the scaling from pilot plant to operation.