Pressure leaching of Çaldağ lateritic nickel ore

Önal, Mehmet Ali Recai
The purpose of this study was to investigate the process optimization of combined high pressure acid leaching (HPAL) and mixed hydroxide precipitation (MHP) route for the extraction of nickel and cobalt from Çaldağ lateritic nickel ore. In order to extract nickel and cobalt values into pregnant leach solution (PLS), several process parameters of HPAL including acid load, temperature, leaching duration and particle size were investigated in comparative manner at constant solid concentration and agitation speed. After HPAL trials, it has been found that more than one combination of parameters offered higher than 90% extraction efficiencies for both nickel and cobalt. Among them, 0.325 kg/kg acid load, 250°C, 1 hour duration and 100% -1 mm particle size was selected as the optimum conditions with 94.1% Ni and 94.0% Co extractions. A stock of PLS was prepared under the stated conditions that was treated by downstream operations in order to obtain MHP. Initially by two-stage iron removal of downstream operations major impurities iron, chromium and aluminum were nearly completely removed with acceptable nickel and cobalt losses from PLS. Then, the nickel and cobalt were precipitated by two-stage mixed hydroxide precipitation. In the first step of MHP, the optimum conditions were chosen as pH=7.10, 60°C and 1 hour duration. The intermediate product obtained at these conditions contained 44.3% Ni, 3.01% Co with 3.06% Mn contamination. In summary, it was found that Çaldağ nickel laterite ore was readily leachable under HPAL conditions and PLS obtained was easily treatable in order to produce saleable MHP.