High pressure acid leaching of a refractory lateritic nickel ore

This paper describes the experimental findings of the extraction of nickel and cobalt by high pressure acid leaching (HPAL) of a refractory limonitic nickel laterite ore from the Gördes region of Manisa in Turkey. By optimizing the basic HPAL process parameters: leaching at 255 °C with 0.30 sulfuric acid to ore weight ratio with a particle size of 100% −850μ for 1 h of leaching, it was found that 87.3% of nickel and 88.8% of cobalt present in the ore could be extracted into the pregnant leach solution (PLS). However, these extraction results were found to be relatively low compared with other similar studies. In order to understand the possible reasons for this relatively lower extraction, further investigations have shown that together with a problem related to the kinetics of the dissolution reactions, a persistent acid resistant refractory mineral present in this sample also limited the leaching process. Attempts were made with different additives to solve this problem. The effects of chemical additives such as HCl, Na2SO4, FeSO4, Cu+ and sulfur were tested and the effect of each addition on the degree of extraction of nickel and cobalt was determined.

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► Leaching temperature, leaching duration, sulfuric acid to ore weight ratio and particle size of the limonitic nickel laterite ore were studied.
► Optimum parameters determined as 255 oC, 0.30 sulfuric acid to ore weight ratio, a particle size of 100% −850μ, 1 h of leaching duration with 30% w/w.
► 87.3% of Ni and 88.8% of Co in the ore extracted into the PLS but, found to be below the desired values due to difficult leaching of primary hematite.
► Heat treatment of the limonitic ore shows that goethite fully transformed to hematite then a tremendous fall in the Ni and Co extractions observed.
► To dissolve the Ni and Co in the primary hematite in the limonitic nickel ore, additions of HCl, ferrous ions, cuprous ions and sulfur were studied.