Research On Microwave Assisted Sulphuric Acid Leaching Of Nickel And Cobalt From Low Grade Laterite Ore

The effects of reaction time, sulphuric acid concentration, temperature and microwave power on the recoveries of nickel and cobalt from laterite ore with sulphuric acid under the effect of microwave irradiation were studied. The results obtained from the experiments of orthogonal array showed that the optimum conditions of microwave power, sulphuric acid concentration, reaction time, and temperature were 600 W, 25% (v/v), 1.5 h, and 90°C, respectively. The kinetics of leaching laterite ore was also investigated. The results showed that the experimental data of the leaching rate accorded with the diffusion-controlled shrinking core model. The apparent activation energy of nickel and cobalt calculated through the Arrhenius equation were 43.0 kJ/mol and 87.7 kJ/mol. Kinetic experiments showed that the leaching of nickel in a sulphuric acid medium was controlled by chemical reaction occurring on the surface of laterite ore, and the reaction of cobalt was controlled by internal diffusion through the porous layer. Cobalt is difficult to leach from the laterite ore with low leaching rate. The main purpose of this paper is to improve the recoveries of nickel and cobalt.The recoveries of nickel and cobalt were 82.7% and 39.7%under a microwave power of 600 W in an 80 mL 25% (v/v) sulphuric acid solution at 90°C for 60 min. In order to heighten recoveries of nickel and cobalt, the different oxidant or reducer additives, such as (NH₄)₂S₂O₈, Ca(ClO)₂, H₂C₂O₄, CuCl, NaNO₂, Na₂S₂O₃, were added during the leaching process. The experiment results were showed as follows: (1) When NaNO₂ was added as additive, the highest recovery of cobalt was 85.2% and reached leaching balance at 5 min; the highest recovery of nickel was 90.5% and reached leaching balance at 60 min. (2) When Na₂S₂O₃ was added as additive, the highest recovery of cobalt was 70.2% and reached leaching balance at 5 min; the highest recovery of nickel was 90.7% and reached leaching balance at 60 min. (3) The recoveries of nickel and cobalt were 86.7%, 85.5%, 85%, 89.3% and 80.7%, 80.6%, 51.5%, 33.5% after adding H₂C₂O₄, CuCl, (NH₄)₂S₂O₈, Ca(ClO)₂, respectively. The recoveries of nickel and cobalt were improved greatly and leaching time was shortened after adding the additives.The advantages of the method of microwave assisted sulphuric acid leaching of nickel from low grade laterite ore are low energy consumption, strong selectivity for leaching, high efficiency of production and low pollution of environment etc. With the further perfection of this process will promote progress of processing technology of laterite ore.