Nickel leaching from laterite ores by combination of organic and sulfuric acid

Abstract

Atmospheric agitation leaching of nickel from laterite ore using sulfuric acid has poor selectivity to iron. This results in a high acid consumption and high iron concentration in the pregnant leach solution. In this study, the leaching behavior of nickel and co-dissolution of iron and magnesium in a mixture of citric acid and sulfuric acid were investigated and compared with those using an individual acid. Series of leaching experiments were conducted under variations of sulfuric and citric acids concentrations in individual and a mixture of these inorganic and organic acids. Kinetics analysis of nickel leaching from limonite ore by a mixture of 2 M citric acid and 0.5 M sulfuric acid and saprolite ore by 0.5M citric acid and 2M of sulfuric acid were also performed. The experimental results obtained in this present research show that citric acid is more effective to be used for saprolite ore than limonite in term of the resulted nickel extraction level. The highest nickel extraction from limonite and saprolite ore by a combination of citric acid and sulfuric acid are 73% and 91%, respectively, after 8h of leaching at 95oC with solid liquid ratio of 5 %, stirring speed 200 rpm using 0.5 M citric acid + 2 M sulfuric acid and 2 M citric acid+0.5 M sulfuric acid, respectively. The leaching kinetics study shows that nickel extraction from limonite ore by a mixture of 2 M sulfuric acid and 0.5 M citric acids is controlled by diffusion through solid product layer, while the nickel extraction from saprolite ore by a mixture of 0.5 M sulfuric acid and 2 M citric acid is controlled by interface reaction with activation energies of 11.47 kJ/mol and 102.36 kJ/mol, respectively.