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Laterite ore is one of the important sources of nickel (Ni). However, it is difficult to liberate Ni from ore structure during reduction roasting. This paper provided an effective way for a robust recovery of Ni from laterite ore by H2 reduction using sodium thiosulfate (Na2S2O3) as a promoter. . It was found that a Ni content of 9.97% and a Ni recovery of 99.24% were achieved with 20 wt% Na2S2O3 at 1,100°C. The promoting mechanism of Na2S2O3 in laterite ore reduction by H2 was also investigated. The thermogravimetric results suggested the formation of Na2Mg2SiO7, Na2SO3, Na2SO4, and S during the pyrolysis of laterite with Na2S2O3, among which the alkali metal salts could destroy the structures of nickel-bearing silicate minerals and hence release Ni, while S could participate in the formation of the low-melting-point eutectic phase of FeS-Fe. The formation of low-melting-point phases were further verified by the morphology analysis, which could improve the aggregation of Ni-Fe particles due to the capillary forces of FeS-Fe as well as the enhanced element migration by the liquid phase of sodium silicates during reduction.

Abstract The large-scale utilization problem of red mud remains a challenge. During the reduction of laterite ores to prepare ferronickel product, sodium or calcium salt usually needs to be added, but it would increase the raw material cost. Thus, the feasibility of co-reduction followed by magnetic separation of strong alkaline waste red mud and a limonitic laterite ore to prepare ferronickel was investigated. A ferronickel product containing 1.71 wt% nickel and 86.00 wt% iron was obtained, under the optimized co-reduction conditions of the red mud dosage of 20 wt%, the anthracite dosage of 16 wt%, the co-reduction duration of 70 min. The corresponding nickel and the total iron recoveries were 96.37 wt% and 97.72 wt%, respectively. Results showed that the co-reduction and comprehensive recovery of the iron ore in the red mud were achieved. [ABSTRACT FROM AUTHOR]

This study investigates the reactions of Na2SO4 and its effects on iron and nickel reduction in the roasting of a high-iron and low-nickel laterite ore through gas composition, X-ray diffraction, and scanning electron microscope analyses. Results showed that a reduction reaction of Na2SO4 to SO2 was performed with roasting up to 600°C. However, no clear influence on iron and nickel reductions appeared, because only a small amount of Na2SO4 reacted to produce SO2. Na2SO4 reacted completely at 1000°C, mainly producing troilite and nepheline, which remarkably improves selective reduction of nickel. Furthermore, the production of low-melting-point minerals, including troilite and nepheline, accelerated nickel reduction and delayed iron reduction, which is attributed to the concurrent production of magnesium magnetite, whose structure is more stable than the structure of magnetite. Reduction reactions of Na2SO4 resulted in weakening of the reduction atmosphere, and the main product of Na2SO4 changed and delayed the reduction of iron. Eventually, iron metallization was effectively controlled during laterite ore reduction roasting, leading to iron mainly being found in wustite and high iron-containing olivine. [ABSTRACT FROM AUTHOR]

In Part II, the correlation between Fe–Ni grain growth and characteristic fusion temperatures of the Na2SO4–laterite mixtures, and phase transformations of the reduced pellets were investigated. For the mechanism of sodium sulphate, Na+is able to liberate the hosted nickel and iron within lizardite, while SO42–is the sulphur source for the formation of Fe–FeS eutectic compound which can decrease the characteristic fusion temperatures to promote the growth of ferronickel grains. The mean particle size of ferronickel increased from 7.4 μm to 48.6 μm with the addition of 20 wt% Na2SO4. [ABSTRACT FROM PUBLISHER]

The selective reduction of nickel and adequate growth of ferronickel grains are imperative for efficient preparation of ferronickel from nickeliferous laterite ore via the process of direct reduction followed by magnetic separation. In Part I, reduction/sulfidation behaviors of a saprolitic laterite ore in the presence of sodium sulfate were investigated, with an emphasis on thermodynamic analysis, selective reduction/sulfidation ratios and kinetics. To separate the interactions between Ni and Fe, chemical titration analysis was adopted to determine the contents of various Ni and Fe species in the roasted pellets, and a modified equation to assay metallic iron content was proposed. [ABSTRACT FROM AUTHOR]

Abstract: A high nickel grade ferronickel was produced from laterite ore using the selective reduction-wet magnetic separation process, with the addition of sodium sulfate (Na2SO4). The ferronickel concentrate assaying 9.87% Ni, with a nickel recovery of 90.90% can be obtained, when laterite ore was reduced at 1200°C for 50min with the addition of 10wt.% Na2SO4 and 2wt.% coal. Based on the results of the X-ray Diffraction, Scanning Electron Microscopy, and Energy Dispersive X-ray Spectroscopy analyses, the thermal decomposition and reduction reaction of Na2SO4 were carried out. Sodium oxide from the thermal decomposition of Na2SO4 reacted with silicate minerals to form nepheline. The formation of the molten phase accelerated the migration rate of the metallic particles and suppressed the reduction of the ferrous minerals in the weak reduction atmosphere. Sulfur reacted with metallic iron to form troilite, thereby facilitating the aggregation of ferronickel particles to form bigger particles. [Copyright &y& Elsevier]

Laterite ores account for >60% of the world's nickel resources. This ore contains considerable amount of scandium, a strategic material in increasingly high demand in various industries. Here, an innovative two-step process was developed in which scandium is first concentrated in a slag phase using carbothermic reduction and then is leached using NaOH cracking process. The byproduct of the first step is metallic iron enriched with nickel and cobalt (ferronickel alloy). The carbothermic reduction process was performed at 1400–1600 °C using lignite as a reductant and calcia and/or silica as a fluxing reagent. A systematic study was carried out using a fractional factorial design methodology to investigate the quantitative effect of four variables. Utilizing the results, an empirical model was built to optimize the process for maximizing scandium concentration. Under the optimum conditions, scandium was successfully concentrated in the slag phase >14 times compared with that in the feed material, while at the same time a high-grade ferronickel alloy was produced. Furthermore, fundamental investigations were performed to elucidate the carbothermic reduction reaction mechanism. For NaOH cracking process, the investigated operating parameters were baking temperature, NaOH-to-slag ratio, baking time, and liquid-to-slag ratio. After optimization, 88% of scandium was recovered, indicating the predictability of the empirical model for scandium recovery. Unlabelled Image • A two-stage process was developed to recover scandium from laterite ore. • Scandium was concentrated in a slag phase using carbothermic reduction process. • Scandium was then leached using NaOH cracking process. • Statistical analyses were used to assess factor effects and to perform optimization. • Fundamental investigations were performed to elucidate the reaction mechanisms. [ABSTRACT FROM AUTHOR]