Innovative methodology for recovering titanium and chromium from a raw ilmenite concentrate by magnetic separation after modifying magnetic properties

Technological research of process for producing titanium rich slag and complex titanium-containing ferroalloy

This paper demonstrates the results on the experimental smelting of the titanium rich slag and complex titanium-containing ferroalloy under the large-scale laboratory conditions that simulate industrial one. The technological researches of the process were performed on an ore-thermal furnace with 200 kVA transformer power. The titanium rich slag was produced from the low-grade ilmenite concentrate, i.e. the low TiO2 content and the high content of impurities. During the production of the high-grade titanium slag (TiO2 content: 75-80%), the impurity elements are transferred into the associated alloyed metal (cast iron). Thus, it can be used to smelt the steel. As a result, samples of titanium slag have been produced with the content of the main components, %: TiO2 - 80.2; Al2O3 - 4.5; SiO2 - 1.97; Cr2O3 - 1.3 and Fe2O3 - 9.87. Then, in metallurgical practice a complex titanium-containing ferroalloy was first smelted from the previously produced titanium rich slag using a carbothermic approach. The high-ash coal was applied as a carbon-bearing reducing agent. The ash was more 45%. As a result of tests, a pilot batch of the alloy was produced with the following chemical composition, %: Ti - 20-25; Si - 35-45; Al - 10-15; C - 0.2-0.5; P - no more than 0.08; and ferrum. The main component content in the produced alloy suggests that it can serve as an alternative to a mechanical mixture (FeSi45, aluminum shavings, low-percentage ferrotitanium) for steel alloying and deoxidation purposes.

Efficient iron recovery from iron tailings using advanced suspension reduction technology: A study of reaction kinetics, phase transformation, and structure evolution

Recycling iron tailings is significant for environmental security and resource recovery, as they contain iron-rich minerals. Given the complex composition of iron minerals and the low grade of iron present in the tailings, innovative suspension roasting-magnetic separation (SRMS) technology was proposed to treat iron tailings that would separate out the iron minerals for recovery. In this study, the reduction kinetics, phase transformation, and structure evolution of the iron tailings were investigated to explain the mechanism behind magnetite production from iron tailings. These studies were conducted using chemical analyses, X-ray diffraction, Brunauer-Emmett-Teller specific surface area, and scanning electron microscopy. The results showed that high temperatures during the suspension reduction process were conducive to improving the reduction rate of the iron tailings. The best kinetics model for this reduction reaction of iron tailings is the P1 model, which demonstrated a linear increase in the conversion degree with the extension of the reaction time. The corresponding mechanism function was f(α) = 1, the apparent activation energy (E_α) was 51.56 kJ/mol, and the kinetics equation was k = 3.14exp(- 51.56/RT). Using the SRMS technology, magnetite gradually formed from hematite, starting at the outer particle layers and moving inward toward the core. The microcracks and pores in the surface of the particles increased, which promoted CO penetration into the particles where it reacted with the hematite. Our results provide important insight into the efficient and clean recycling of iron tailings.

A semi-industrial experiment of suspension magnetization roasting technology for separation of iron minerals from red mud

Red mud is a type of solid waste derived from the alumina extraction process. It can be considered as a secondary resource for recovering iron values because of its high content of ferric oxide. In this study, an innovative technology called suspension magnetization roasting (SMR) was applied to treat red mud to recycle iron. Based on the lab-scale experimental basis, we adopted the single factor method to perform the semi-industrial scale experiments. Under the optimum conditions, the recovery and grade of iron in the iron concentrate were 95.22 % and 55.54 %, respectively. Chemical phase analysis, vibrating sample magnetometer, and XRD combined with Mössbauer spectroscopy were employed to assess the characteristics of red mud and roasted products. Occupancy of Fe content in magnetite was raised to 89.91 % in SMR products from 0.75 % in the red mud; saturation magnetization was enhanced from 0.40 A·m²/kg to 32.44 A·m²/kg; and the hematite and goethite phase were transformed into Fe₃O₄ (A), Fe₃O₄ (B) and γ-Fe₂O₃ phase. In addition, transmission electron microscopy analysis revealed that both magnetite and maghemite were found in the roasted product. This study demonstrates that SMR is a promising technology for the recovery of iron from red mud.

Influence of Hydrofluoric Acid Leaching and Roasting on Mineralogical Phase Transformation of Pyrite in Sulfidic Mine Tailings

Under the oxidative roasting process, pyrite, as a major mineral in sulfidic mine tailings, can transform to iron oxides. Generated iron oxides, if exhibiting enough magnetic properties, can be recovered via magnetic separation resulting in partial mine tailings valorization. However, due to the presence of various minerals and sintering possibility, it is advantageous to remove impurities and increase the pyrite content of mine tailings prior to the roasting procedure. In this case, hydrofluoric acid that has no influence on pyrite can be used to leach most inorganic minerals, including aluminosilicates. Therefore, this study investigated and compared the influence of the roasting process with and without hydrofluoric acid leaching pretreatment on mineralogical phase transformation of pyrite and magnetic properties of thermally generated minerals. Several tests and analyses were performed to study mineralogical phase transformation, morphology, elemental composition, surface characterization, and magnetic properties. Results of this study indicated that without acid leaching pretreatment, pyrite was mainly transformed to hematite. However, via acid leaching, fluorine, as a more electronegative element over oxygen, entered the compound and neglected the role of oxygen in thermal oxidation, instead reducing sulfur content of pyrite to only form pyrrhotite.

Formation of zinc sulfide species during roasting of ZnO with pyrite and its contribution on flotation

In this paper, formation of zinc sulfide species during roasting of ZnO with FeS₂ was investigated and its contribution on flotation was illustrated. The evolution process, phase and crystal growth were investigated by thermogravimetry (TG), X-Ray diffraction (XRD) along with thermodynamic calculation and scanning electron microscopy-Energy-dispersive X-ray spectroscopy (SEM-EDS), respectively, to interpret the formation mechanism of ZnS species. It was found that ZnS was initially generated at about 450 °C and then the reaction prevailed at about 600 °C. The generated Fe_xS would dissolve into ZnS and then form (Zn, Fe)S compound in form of Fe₂Zn₃S₅ when temperature increased to about 750 °C. This obviously accelerated ZnS phase formation and growth. In addition, it was known that increasing of ZnO dosage had few effects on the decomposition behavior of FeS₂. Then, flotation tests of different zinc oxide materials before and after treatment were performed to further confirm that the flotation performances of the treated materials could be obviously improved. Finally, a scheme diagram was proposed to regular its application to mineral processing. It was systematically illustrated that different types of ZnS species needed to be synthetized when sulfidization roasting-flotation process was carried out to treat zinc oxide materials.