ENK has commercialised a proprietary, low cost heap leach process for nickel laterites.
ENK has demonstrated the percolation and extraction of nickel at a large scale demonstration plant at Çaldag in Turkey with continuous operations over a three year period, irrigating the heaps with dilute sulphuric acid and producing saleable mixed hydroxide product from the downstream precipitation plant. Recoveries of 72% have been used in the Çaldað bankable feasibility study for both nickel and cobalt.
The pregnant solution from the leach is collected in ponds and recirculated through the heaps to maximise the metal content before being pumped to the precipitation plant. First the iron content is precipitated by raising the pH level, which is thickened and filtered and disposed of as the only waste product from the process. Then the liquor from the iron thickener is treated by raising the pH further with soda ash to produce a nickel-cobalt hydroxide precipitate with a nickel content of above 30% that is filtered and packaged in bulk bags which are placed in containers for shipment.
Environmental Benefits of Heap Leach Technology
ENK believes that the heap leach technology it has developed provides significant environmental benefits over conventional nickel laterite operations. Operation of the heap leach in close proximity to the mine minimises the transport distances for the unrefined ore, thereby reducing truck movements on roads.
The heap leach technology also considerably reduces the carbon dioxide emissions generated per tonne of nickel produced when compared to conventional nickel laterite operations. ENK is assessing options to improve this reduction further through conventional means such as tree planting and CO2 capture.
The conversion of sulphur to sulphuric acid at each site’s acid plant releases energy which can be used to create steam and in turn generate electricity which will be in excess of the project’s needs. The sulphuric acid is entirely used up in the heap leaching process. The excess power generated will be sold to the local electrical grid which will reduce the requirement for the grid to be supplied with electricity generated by burning fossil fuels.
