Study On Sulphuric Acid Pressure Leaching Of A Laterite From Yuanjiang In Yunnan Of China

Pressure leaching has been used in the extraction process of zinc, copper, manganese and aluminum since it was brought forward. Pressure acid leaching of nickel laterites has the advantages of high nickel and cobalt recoveries and effective separation of iron, alumium and silicon from nickel and cobalt, therefore it will become the preferred technology for laterites processing in the future. Until recently, there has been no systematic research on the pressure leaching of Yuanjiang laterite ore in Yunnan, China, which contains maghemite and magnetite. In this paper, the pressure leaching of Yuanjiang laterite was studied. The results will be helpful to the processing of Yuanjiang laterite ore.In this paper, the factors affecting metal extraction such as temperature, acid to ore ratio, agitation rate and leaching time were investigated. The results indicate that acid to ore ratio and temperature are the leading factors influencing nickel and cobalt extractions and iron and aluminium contents in the leach liquor. As the leaching temperature increases, nickel and cobalt extractions increase and the contents of iron and aluminum in the leach liquor decrease. The nickel and cobalt extractions increase with the increase of acid to ore ratio, however, high acidity leads to the increase of acid consumption and inhibits the hydrolysis of iron and aluminium. Increasing agitation speed can enhance the hydrolysis of iron and aluminium.The optimal conditions for leaching of Yuanjiang laterite ore are as follows:temperature 270℃, acid to ore ratio 0.7:1 (g/g), liquid to solid ratio10:1(g/g), agitation speed 450r/min and leaching time 45min. Under these conditions, nickel, cobalt, iron and aluminium extractions can reach 99.67%,93.42%,13.88% and 20.10%, respectively. The acid consumption is 518.5g acid/kg ore.The leaching behaviour of the minerals in Yuanjiang laterite ore during pressure acid leaching and the composition of the solid residues were studied using X-ray diffraction and scanning electron microscopy /X-ray energy dispersive spectroscopy. Lizardite and goethite are leached preferentially to maghemite and magnetite. Maghemite and magnetite are dissolved completely at 270℃. The dissolution of the main iron minerals such as goethite, maghemite and magnetite increase with the increases of temperature, acid to ore ratio and leaching time. Hematite, alunite and silicon oxide are the dominant phases of the solid residues. Minor nickel and cobalt are adsorbed to the surface of the solid residues or co-precipitation with hematite, alunite and silicon oxide.The kinetics of sulphuric acid pressure leaching of Yuanjiang laterite ore was also investigated. The leaching kinetics accords with the unreacted shrinking core model. Interfacial chemical reaction is the rate-controlling step of the leaching reaction. The kinetic equation of the leching reactions of nickel and cobalt is 1-(1-x)1/3=k-t. The activation energy for the leching reactions of nickel and cobalt are 41.41 kJ/mol and 43.70 kJ/mol, respectively.