Dissolution behaviour of a Turkish lateritic nickel ore

The atmospheric pressure sulphuric acid leaching characteristics of Adatepe (Eski?ehir, Turkey) laterite ore that has recently been put into operation was investigated. The effects of sulphuric acid concentration (5-95%), temperature (20-95 °C) and time (30-240 min) on leaching were determined by nickel, iron and arsenic analyses. The amounts of Ni, Fe and As in solution were observed to increase with increase of temperature from 20 °C to 70 °C for sulphuric acid concentrations between 5% and 95%. Further increase of temperature to 95 °C showed that the dissolution of Ni, Fe and As were increased until 60% sulphuric acid concentration and over 60% a decrease in the dissolution percentages was observed due to the probable formation of nickel and silicon containing ferric sulphate type compounds that cause nickel loss from the leach solution. Experimental results showed that maximum nickel dissolution of 99.2% at 95 °C could be reached in 120 min of leaching time for a sulphuric acid concentration of 60%. The congruency of Ni dissolution with respect to Fe was found to be congruent over about 25% Ni and 15% Fe dissolution values. XRD analyses on the residues obtained after leaching showed that it was not required to dissolve all goethite phase to reach maximum dissolution of nickel contained in the sample. An activation energy of 30.36 kJ/mole was determined for Ni dissolution showing that leaching is controlled by external diffusion and chemical reactions.