Study On Mechanism And Technology Of Selective Reduction-Magnetic Separation To Concentrate Nickel From Low Grade Laterite Ore

The rapid expansion of domestic stainless steel manufacture dramatically increased demand for nickel in recent years. Study on using low grade laterite ore to produce ferronickel is in the ascendant. With the funding of National Natural Science Foundation of China (Theoretic Study and Process Development on Manufacturing High Nickel Concentrate from Low Grade Laterite,50974135,2010) and National Development and Reform Commission (Key Technology for Highly Efficient Utilization of Low Grade Laterite, NDRC-Hitech Office 2009-606,2009), this paper has been focused on the mineralogical study of low grade laterite ore samples from Indonesia and selective reduction-magnetic separation process to manufacture high nickel grade concentrate from laterite. This work also conducted study on raw laterite mineralogy, mechanism of selective reduction, optimization of selective reduction parameters, and both nickel and sulphur behavior during reduction.The study of mineralogy and crystal chemistry of raw laterite ore sample found that:the limonitic sample consists of some 80%and 13% silicate minerals. Goethite and silicates are the Ni host phases which contain 0.87 % and 1.19 % Ni, respectively. The saprolitic sample consists of some 65% silicate minerals and 30% goethite. Silicates and goethite are the Ni host phases, which contain 1.07% and 1.59% Ni respectively. Cobalt was mostly found occurring in asbolane from both laterite ore samples.The thermodynamic study of nickel laterite selective reduction found that:from the thermodynamic viewpoint, under the conditions that the CO concentration between 10% to 50% and temperature between about 435℃to 720℃, the selective reduction of NiO over FeO could be achieved. From the industrial practice, however, this is too strict to be conducted. The addition of silica and sulphur was reported to be beneficial both to selectivity of the reduction and the growth of nickel metallic.The optimization of selective reduction-magnetic separation process found that:Concentrate assaying 5.1% nickel could be manufactured from single limonitic laterite ore sample with nickel recovery of 98.79%. The reduction was conducted under the conditions that 3.0% additive and 3.0% coal was added, blend basicity at 0.07 and the calcination was carried out at 1250℃for 60 min. When 40.0% SN laterite sample,5% reductant and 6.0% CaSO4 was added, the LN sample was calcinated at 900℃for 15min and then 1100℃for 60 min. Concentrate assaying 6.01% nickel was thus manufactured at a recovery of 92.08%.The Mineralogy and crystal chemistry study of reduced sample found that:main phase of reduced sample was y Fe-Ni, wustite, spinel et al.. Relatively high Ni was observed from y Fe-Ni, whereas Fe was mainly presented in wustite and spinel, the selective reduction was thus achieved. The present of sulphur contributed more formation of metallic phase with size over 10μm, the mean size of y Fe-Ni particles were increased from 5.8μm to 16.1μm after the additive was added. Iron monosulphide was observed as well as Fe-Ni-Co solid solution which with high nickel concentration, but no nickel sulphide, due to the replacement reaction between Fe and Ni/CoS. The thermodynamic theories and phase diagram successfully predicted the selective reduction and mechanism of sulphur behavior.