As the fourth-largest industry waste residue, after iron slag, steel slag, and red mud, in China, the comprehensive utilization of nickel slag is imminent. Coal-based reduction combined with magnetic separation was considered an efficient method to extract iron from nickel slag. During the coal-based reduction of Jinchuan ferronickel slag, the growth characteristics and kinetics of metallic iron were investigated in this paper. The metallisation rate and metal iron grain size gradually increased with the reduction temperature or the reaction time, and the coal-based reduction process was divided into the rapid formation period and the aggregation growth period of the metallic phase. The granularity distribution of metallic iron obeyed the Doseresp sigmoidal function, and the activation energy of grain growth at different stages were 52.482 ± 4.448 kJ·mol⁻¹ and 26.426 ± 3.295 kJ·mol⁻¹, respectively. Meanwhile, a mathematical growth model of the metallic iron grains was also established.

In this study, a novel technology for the comprehensive utilization of low-grade iron ore is presented. For the iron ore with a Fe content of 24.91%, a pilot-scale study of pre-concentration, suspension magnetization roasting, grinding, and low-intensity magnetic separation was conducted, and an iron concentrate with a grade of 62.21% and a recovery of 85.72% was obtained. The products were analysed using chemical elemental analysis, particle size analysis, X-ray diffraction, scanning electron microscopy, and vibrating sample magnetometry. The results indicated that hematite was reduced by CO and H₂ mixture and transformed into ferrimagnetic magnetite in the suspension magnetization roasting, which was easily recovered in the subsequent magnetic separation. Additionally, a pre-concentration tailing with a SiO₂ content of 81.55% and a magnetic tailing of the roasted ore with a SiO₂ content of 79.57% were obtained, which can be used as building materials. This presents significant implications for the comprehensive utilization of low-grade iron ore.

In the present paper, high-voltage pulse discharge (HVPD) was proposed to enhance the separation characteristic of magnetite quartzite. The technical indicators of concentrate grade 61.76% and recovery 83.26% were obtained at pulse number 90, loading voltage 35 kV, and grinding time 9 min. The liberation of breakage products was improved by 26.81 percentage points via HVPD. The liberation of grinding products also increased significantly via HVPD, whereas the advantage of HVPD was weakened by the extensions of grinding time. The magnetism of magnetic separation concentrate is significantly enhanced after high-voltage pulse discharge pretreatment, which is conducive to the efficient separation of magnetite quartzite. Quantum chemical computation showed that the bandgaps of magnetite and quartz were 0.155 and 5.797 eV, respectively. Scanning electron microscope (SEM) analysis indicated that a lot of pores were generated on the surface of HVPD products. Dans le présent article, on a proposé la décharge d’impulsion à haute tension (HVPD) pour augmenter la caractéristique de séparation de la magnétite-quartzite. On a obtenu les indicateurs techniques de 61.76% de la qualité du concentré et 83.26% de la récupération à 90 impulsions, 35 kV de charge du voltage et une durée de broyage de 9 min. La libération des produits de fragmentation était améliorée de 26.81% via HVPD. La libération des produits de broyage a également augmenté de manière significative via HPVD, alors que l’avantage de HVPD était affaibli par les extensions de temps de broyage. Le magnétisme du concentré de séparation magnétique est augmenté de manière significative après le prétraitement par décharge d’impulsion à haute tension, ce qui conduit à la séparation efficace de la magnétite-quartzite. Le calcul chimique quantique a montré que la bande interdite de la magnétite et du quartz était respectivement de 0.155 eV et 5.797 eV. L’analyse au microscope électronique à balayage (MEB) a indiqué qu’un grand nombre de pores étaient engendrés à la surface des produits de HVPD. GRAPHICAL ABSTRACT