The high magnesium nickel laterite ore need first be dehydrated if it is treated by the pirometallurgical means. The nickel laterite ore was dehydrated in a laboratory scale sintering pot in this study. The dehydration mechanism was studied by using the thermo-gravimetric (TG) tests, differential thermal analysis (DTA), and X-ray diffraction (XRD) experiments. The measurements indicated that chlorite (Fe,Mg,Al)6(Si,Al)4O10(OH)8 and serpentine Mg21Si12O28(OH)34H2O are the primary phases, while FeO(OH) and (Fe,Mg,)3Si4O10(OH)2 are the minor phases in the ore. The water in the ore can be divided as free water, crystal water, and hydroxyl group. During the heating process, the temperature range for the removal of the free water is 25~140˚C, for the crystal water it is 200~480 ˚C, and for the hydroxyl group it is 500~800˚C. The experiments with various coal dosages show that the temperatures of off-gas and burden increase with an increase in coal dosage. The sinter samples were analyzed using XRD. The results demonstrated that olivine (Mg,Fe)2SiO4 and spinel MgFe2O4 are the main bonding phases
In consideration of the abundant moisture of limonitic nickel laterite mined, it is essential to determine whether the self-possessed moisture of limonitic nickel laterite after pre-dried is appropriate for sintering. Thus, based on the characterization of limonitic nickel laterite, the influence of its self-possessed moisture on sintering performance was expounded by sinter pot tests and the relevant mechanism was revealed by the systematical analyses of the granulation properties of sinter mixture, thermodynamic conditions during sintering and mineralogy of product sinter. The results indicate that the self-possessed moisture of limonitic nickel laterite indeed has significant influence on its sintering performance. At the optimum self-possessed moisture of 21 mass%, sinter indices are relatively better with tumble index, productivity and solid fuel rate of 48.87%, 1.04 t m−2 h−1 and 136.52 kg t−1, respectively, due to the superior granulation properties of sinter mixture and thermodynamic conditions during sintering, relatively large amount of silico-ferrite of calcium and alumina and tighter sinter microstructure. However, sintering performance of limonitic nickel laterite is still much poorer than that of ordinary iron ores. It is feasible to strengthen limonitic nickel laterite sintering by inhibiting the over-fast sintering speed and improving the thermodynamic conditions during sintering.
Limonitic laterite contains low iron and nickel grades and much high smelting minerals and loss on ignition (LOI), identified as refractory iron ore for sintering. Thus, sinter pot tests of limonitic laterite via pressurized densification sintering and its intensification mechanism were conducted, and the industrial application prospect was explored. The results indicate that the sintering performance of the limonitic laterite of the new process is significantly improved with the tumble index and productivity increased by 19.2% and 18.6%, respectively, and solid fuel rate lowered by 10.3%. The external pressure field promotes the synchronization of heat front velocity and combustion front velocity for better sintering heat and mass transfer conditions, which also greatly improves the mineral compositions and microstructure of the product sinter. The microstructure is converted from large thin-wall pores into small thin-wall or large thick-wall pores with the sinter porosity decreased by 42.4%. Much close interlocking texture between hercynite and silico-ferrite of calcium and alumina (SFCA) is formed with hercynite grains aggregation and growth, and SFCA amount substantially increased. The better sintering performance will bring about a remarkable economic benefit of 282.78 million RMB/a if the industrial application is implemented. The pressurized densification sintering process is considered as one of the effective technologies for improving limonitic laterite sintering.
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