Atmospheric pressure acid leaching of Caldag lateritic nickel ore

•Coarser Caldag lateritic nickel ores were leached more readily.•The greatest extraction of Ni, Co and Fe was achieved at a 10/1 liquid-to-solid ratio.•Nickel and iron were easily leached from the coarse particle size fraction.•More than 90% of Ni and Co were extracted from Caldag lateritic nickel ore.

Nickel, cobalt and iron were extracted from Caldag lateritic nickel ore under atmospheric pressure acidic leaching conditions. The following variables were examined to understand their effects on extraction: sulphuric acid concentration, liquid-to-solid ratio, leaching temperature, leaching time, and particle size. After 6 h of leaching, 91.9% Ni, 93.5% Co and 80.5% Fe were obtained under the following conditions: 2 M H2SO4, 90 °C, liquid-to-solid ratio = 10/1(mL/g), stirring speed = 500 rpm, and laterite particles < 0.053 mm. The results indicated that there is no benefit gained in the leaching of nickel by grinding finer than 0.150 mm under the conditions explored, whereas the greatest cobalt extraction was achieved with the use of the finest particles. XRD and SEM–EDX results verified that nickel was associated with asbolane, goethite/hematite and clay-like mineral phases. In addition, kinetic analyses of the nickel extraction revealed an activation energy of 51.6 kJ/mol.

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