Abstract
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.
Highlights
Nickel, as a ferromagnetic metal with a high corrosion resistance, plasticity, and magnetism, has been intensively used in many applications involving nickel-based alloys and stainless steel as well as in fuel cells (Sudagar et al, 2013)
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
The reaction mechanism is described as follows: 1) During the heating step, Na2S2O3 decomposed to S, Na2SO4, and Na2S. 2) S reacted with iron oxides, which decomposed from goethite in the laterite nickel ore to form FeS; Na2SO4 and Na2S destroyed the structures of the nickelbearing silicate minerals at higher temperatures, releasing the nickel wrapped in magnesium-containing silicate minerals and forming a low-melting-point eutectic phase (Na2Mg2Si2O8). 3) During the H2 reduction stage, NiO and iron oxide were reduced to their metal phases, after which the fine nickel and iron particles directionally aggregated and grew with the help of FeS-Fe
Summary
As a ferromagnetic metal with a high corrosion resistance, plasticity, and magnetism, has been intensively used in many applications involving nickel-based alloys and stainless steel as well as in fuel cells (Sudagar et al, 2013). Lu et al (2013) investigated the effect of sodium sulfate on the hydrogen reduction process of nickel laterite ore. Limited studies on this topic have been reported, especially the effect and mechanism of sodium thiosulfate on promoting the laterite ore reduction. In current study, sodium thiosulfate was employed to improve the grade and recovery of nickel by hydrogen reduction of laterite followed by magnetic separation. Based on the collected data, the promotion mechanism of sodium thiosulfate for hydrogen-thermal reduction of laterite ore was proposed. After the reduction process was complete, the ore samples were cooled to room temperature under a nitrogen atmosphere (0.1 L/min). The main chemical composition of nickel laterite ore and the contents of Fe and Ni in each sample were determined by inductively coupled plasma atomic emission spectrometry (ICP-AES-9000(N + M), a commercial product of Thermo. Where WL is the net weight loss; mT is the mass of the sample at the temperature of T; m1050 is the mass of the sample at 1050°C; and m is the initial mass of sample
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