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In this study, reductive roasting followed by low-intensity magnetic separation were used to upgrade iron ore from Gua mines in Jharkhand. The work aimed to maximise the recovery of iron values by upgrading to a high-grade product suitable for pelletisation and sintering. The received ore contains 58% Fe, 7.82% silica, 4.26% alumina and 4.97% loss...
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... thermal analysis/thermogravimetric analysis (DTA/TG) in Figure 5 reveals that one endothermic and two exothermic peaks were observed. The first exothermic peak is due to the release of moist- ure at 100°C and in DTA endothermic peak at 350°C indicating that maximum heat was absorbed by the sample. ...
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... This suggests that regardless of particle size, the reduction temperature does rise with the level of metallization degree and reduction degree. The presence of ash layer diffusion into the dense microporous structure also contributes to the reaction rate controlling resistance, according to initial preliminary investigations from the literature [38,39]. But compared to other kinetic models, higher apparent Ea values and slower chemical reaction activity between the gaseous carbon-monoxide and iron ore based on the shrinking core model now the rate controlling resistance. ...
... In order to distinguish it from natural magnetite, magnetite obtained by magnetization reduction roasting is called artificial magnetite. Thermodynamic studies indicate that oolitic hematite can be converted into strong magnetic artificial magnetite through magnetization reduction roasting, suggesting its theoretical feasibility [16][17][18][19][20][21]. However, the dense structure and fine dissemination of oolitic hematite pose challenges during magnetization roasting, leading to high CO diffusion resistance and the occurrence of under-reduction or over-reduction. ...
Magnetization reduction roasting is an important method for the utilization of oolitic magnetite. In this study, the magnetization reduction behavior and kinetics of oolitic hematite in gas-based roasting were systematically investigated by X-ray photoelectron spectroscopy (XPS). The results revealed that under optimal roasting conditions of 650 °C, a roasting time of 60 min, and a CO concentration of 30%, the magnetization reduction rate of the roasted product reached 44.34%. Furthermore, the weak magnetic separation concentrate presented a TFe of 58.09% and a concentrate iron recovery of 94.3%. The results of the XPS spectrum indicated that the peak area ratio (Fe2+/Fe3+) gradually increased with an increase in roasting temperature, roasting time, and CO concentration, while over-reduction occurred when the roasting temperature exceeded 750 °C. The investigation of magnetization roasting kinetics for varying particle sizes demonstrated that the magnetization reduction process is controlled by chemical reaction, with a corresponding activation energy range of 42.96 kJ/mol to 63.29 kJ/mol, indicating the particle size has little effect on the magnetization reduction of oolitic hematite.
... The propagation of this crack proceeds when the reduction temperature is between 900 and 1000 • C. Thus, thermal and volume expansion does favor reducing gas porosity, which propagates cracks and increases iron whisker growth within the iron ore metal matrix during reduction. The increase in gangue contents as shown in Table 3 and Table 4 may also hinder the growth of whiskers, especially when formidable binders (i.e., bentonite, molasses) are used during the pelletization and beneficiation process [28]. However, this process can be energy-demanding and time-consuming since the novelty of this study was to minimize and control the amount of carbon deposition in directly reduced iron in the conventional iron processing technology [29]. ...
Non-contact direct reduction (NDR) is an alternative technique in iron and steelmaking. Direct reduced iron production (DRI) uses it. To further harness the metallurgical and operational capabilities of the process for its suitability as an alternative feed in the blast furnace process, there is a need to study the effect of the reduction parameters on the weight loss, crack propagation level, gas porosity, iron whisker growth, and morphological characteristics of the DRI. Thus, this paper attempts to utilize the NDR process using commercially acquired goethite-hematite ore in a carbon-monoxide atmosphere from wood charcoal under specified isothermal conditions, with a reduction temperature range from 570, 800, and 1000°C. The effect of reduction parameters on weight loss, crack propagation, iron whisker growth, and morphological properties of the DRI was investigated using standardized reduction reaction practices under a nitrogen gas atmosphere with a flow rate of 120 mL. Mineralogical and morphological analyses of the direct reduced iron (DRI) and charcoal were performed using XRF and SEM/ED analysis. Proximate and ultimate analyses of the reductant were performed to ascertain their physical and chemical properties. The results show that reduction parameters tremendously influence the weight loss, crack propagation, gas porosity level, and metallurgical quality of the DRI. The reduction degree and swelling extent of the DRI also increase with crack propagation and iron whisker growth. Thus, the overall reduction mechanism still follows the usual stepwise chronological reduction order (Fe2O3 → Fe3O4 → FeO → Fe) regardless of temperature, with ash layer control being the reaction rate control. The NDR technique shows no carbon deposition in the DRI metal matrix. It indicates that this approach can serve as a viable alternative for DRI production in the ironmaking process.
... Wu et al. [48] investigated the morphological changes of goethite within the temperature range of 0-1000 • C. The conversion of goethite to hematite was classified into three categories, namely, inert zone, dihydroxylation zone, and recrystallization zone, as shown in Fig. 12. Adding a reducing agent converted goethite and Al-goethite to magnetite during thermal conversion, with the transformation temperature varying depending on the species of reducing agents [131,132]. A total iron grade of about 66.6% with iron recovery of approximately 90.4% could be obtained by reduction roasting goethite-rich iron ores using 10% coal at 800 • C for 30 min, followed by low-intensity magnetic separation [133]. According to the literature [134], a suitable temperature for converting goethite to magnetite through reduction roasting was between 650 • C and 700 • C in the atmosphere of 50%/50% CO/CO 2 . ...
In 2021, global alumina production reached over 135 million tons and discharged approximately 200 million tons of red mud, leading to severe environmental safety hazards. More than 70% of raw materials originated from gibbsitic bauxite. This work reviews existing and potential process from open literature to treat gibbsitic bauxite and reduce red mud discharge from the alumina production process, which are divided into two categories. The first strategy involves non-Bayer methods such as smelting reduction, reduction roasting, sub-molten salt, ammonium sulfate roasting, acid leaching, and calcification–carbonation. The current obstacle to implementing these methods is the lack of economics, making industrial application challenging. The second potential industrial application strategy is to modify the current Bayer process, with critical measures involving the enhancement digestion of inert aluminum-bearing minerals, dissociation and recovery of iron minerals, and separation of desilication products. Analyzing the reaction mechanism and process flow clarify that the modified Bayer method is more favorable to the cost-effectively and synergistic extraction of aluminum, iron, and other elements. The red mud obtained by the modified Bayer process can be efficiently utilized. Therefore, a mini-summary of the areas where red mud is expected to be substantially dissipated (e.g., the steel industry, cement building materials, and ecological restoration of red mud stockpiles) is provided. The review can advance the current technology on the comprehensive utilization of gibbsitic bauxite, especially process discharge reduction approaches and large-scale abatement ways for red mud. Our results can contribute to the future development of sustainable green alumina production.
... Roasting and reduction processes. Adapted from [24] Hematite reduction can be influenced by impurities present in the ore. Therefore, research has been carried out to perform magnetic separation after roasting low-grade iron ore [25,26]. ...
... Roasting and reduction processes. Adapted from Ref.[24]. ...
This research is aimed at the up-gradation of indigenous Pakistani iron ore, i.e., Dilband iron ore (hematite), by utilizing common metallurgical processes. First, the magnetic properties of the ore were determined. Initially, the iron ore samples contained 34 wt. % Fe in addition to other gangue materials. Therefore, the ore was subjected to a high-temperature reduction roasting process between 800 • C and 1000 • C. Additionally, the magnetic separation process was also employed. The influence of different roasting parameters, such as the reduction time, coal-to-ore ratio, and temperature, was examined. This was followed by characterization techniques using XRD (X-ray diffraction analysis), the Rietveld method, wet chemistry analysis, and a VSM (Vibrating Sample Magnetometer). The results suggest an excellent reduction at 900 • C for a coal/ore ratio of 20 wt. %, which was achieved within 2 h of the process. The Fe concentration increased tremendously from 34 to 56 wt. %, and in conjunction, magnetic properties were also induced (1.5 emu). The recovery was found to be substantial for the ore when the Fe content was 75 wt. %. Additionally, the economic feasibility of the processed ore was also studied, followed by an extensive analysis of the roasting and magnetic separation processes.
... The size fractions of studied materials were quite small, having particle sizes less than 0.1 mm. In [19,20], coarse-grained ores were used, but the initial iron content was also high (more than 50 wt.%). ...
... The roasting temperature ranges from 500 °C for roasting with CO [21] or biomass [22] to 800 °C for roasting with coal [2,3,20,23]. The higher temperatures for roasting with coal is associated with the starting temperature of its gasification of 700-750 °C. ...
Iron-bearing wastes are permanently accumulating, and increasing the use of low-grade ores only accelerates this tendency. In addition to huge area occupation, iron tailings impose several risks associated with environmental pollution by toxic substances and extremely small particles. Consequently, an urgent problem of metallurgy is utilization of iron-bearing wastes with iron recovery. In this paper, composition, granulometric properties and beneficiation of tailings from the Central mining and processing plant in Kryvyi Rih, Ukraine have been studied using X-ray diffraction, X-ray fluorescence, microscopy, and magnetization measurements. The beneficiation has been conducted using magnetizing roasting with carbon monoxide followed by dry low-intensity magnetic separation. Initial tailing materials, sampled at different distance from the slurry pipeline of the tailing pond, consisted mainly of quartz (34-80 wt.%) and hematite (13-58 wt.%), in addition to minor goethite (~3 wt.%) and magnetite (0.7-1.7 wt.%). The content of hematite correlates with the amount of iron, decreasing from 53 to 26 wt.% as the distance from the slurry pipeline increases to 500 m. The results of particle size analysis showed that the tailings were represented by fine-grained material with a predominant fraction <0.05 mm. Chemical and mineralogical analysis revealed uneven distribution of hematite and quartz between different granulometric fractions. In general, the content of hematite and total Fe decreased as the size fraction increased. Magnetizing roasting of raw samples and granulometric fractions <0.05 mm, 0.063-0.071 mm, 0.071-0.1 led to a significant change in mineral composition and magnetic properties. The transformation of hematite and goethite into magnetite reduced the mineralogical complexity of the tailing materials, resulting in an enhance in mass magnetization to 11-62 Am2/kg in comparison with initial values 0.3-1.5 Am2/kg. After magnetic separation, X-ray diffraction analysis confirmed that the magnetic concentrates consisted almost completely of magnetite and non-magnetic residues contained major quartz. The saturation magnetization of the concentrates increased to 75-88 Am2/kg. It was shown that the content of iron in magnetic concentrates reached 68.5-70.2 wt.% and iron recovery 77-96 wt.%, depending on size fraction. The results of this article shows that the tailings are represented by fine-grained liberated material with variable Fe content that can be upgrade using magnetizing roasting and magnetic separation into two valuable products, such as iron concentrate and silica powder.
... Moreover, the complete conversion of goethite to magnetite can be achieved at different temperature ranges: at 500-600 °C in (Wu et al., 2012), 700 °C in (V. P. , and 800 °C in (Ravisankar et al., 2017). The latter correlates well with the results obtained in this article. ...
Mineral and magnetic transformations can be very helpful in processing low grade iron ores by increasing the iron content, removing impurities or improving the magnetic susceptibility. But the pathways and conditions of this transformations can be very divergent for various type of iron ores, depending on structure, mineral and chemical compositions. In this work, mineral, chemical, and granulometric properties of low-grade iron ores from the Ingulets deposit, Kryvyi Rih basin, Ukraine have been studied in addition to their oxidative and reductive roasting. The initial samples of banded hematite quartzites (BHQs) are represented by equigranular grains of quartz and hematite of <0.1 mm. Goethite-hematite quartzite has a non-uniform structure, in which the disperse goethite contains larger grains of hematite, quartz and kaolinite. The major chemical components of hematite quartzite are Fe2O3 (31-32 wt.% of Fe) and SiO2, while goethite-hematite quartzite exhibits a higher content of Al2O3 and Fe2O3 (42.5 wt.% of Fe), as well as lower content of SiO2. Granulometric analysis of hematite quartzite reveals uneven distribution of minerals and total iron between different size fractions. An almost complete liberation of hematite grains in the crushed ore is observed in the granulometric fractions of 0.05-0.1 mm (more than 80%) and <0.05 mm (about 90%). Oxidative roasting of ores leads to weight losses in the range of 0.5-8%, implying the thermal decomposition of goethite to hematite and siderite to magnetite. The latter also leads to a slight increase in the magnetization of the sample at 600 °C. Reductive roasting results in a significant increase in magnetization associated with the formation of magnetite starting at 300 °C, while a complete conversion of hematite and goethite occurs at 500-600 °C. At temperatures higher than 700 °C, the conversion of magnetite to antiferromagnetic wüstite was observed for all samples, resulting in a decrease in magnetization. Hence, reductive and oxidative roasting of low-grade iron ore of the Ingulets deposit result in magnetic and chemical modifications that can be considered as a promising preparatory technique for further processing.
... The experimental results confirm that the conveyor bed process system is effective for the application of the magnetized roasting of siderite. The use of a three-stage suspension cooling process enables rapid cooling of the roasted ore to <200 °C and prevents the oxidation of magnetite [28][29][30]. The low hematite (magnetite) content of the roasted ore confirmed that the cooling process was effective. ...
Upgrading and utilizing low-grade iron ore is of great practical importance to improve the strategic security of the iron ore resource supply. In this study, a thermal analysis–infrared (IR) analysis–in-situ IR method was used to investigate the reaction mechanism and kinetics of Daxigou siderite. Experiments were conducted using a conveyor bed magnetization roasting process (CBMRP) to investigate the magnetization of siderite. Multi-stage magnetic separation processes were adopted to extract magnetite. The results show that simultaneously the iron carbonate in siderite decomposes, and magnetite is formed between 364 °C and 590 °C under both inert and reducing atmospheres. The activation energy of the magnetization roasting reaction is 106.1 kJ/mol, consistent with a random nucleation and growth reaction mechanism. Magnetization roasting at 750–780 °C for approximately 3.5 s in the CBMRP results in a magnetic conversion rate of >0.99% of the iron minerals in the siderite. A beneficiation process of one roughing, one sweeping, and three cleaning processes was adopted. A dissociation particle size of −400 mesh accounting for 94.78%, a concentrate iron grade of 62.8 wt.%, and a recovery of 68.83% can be obtained. Overall, a theoretical and experimental basis is presented for the comprehensive utilization of low-grade siderite.
... A beneficiation of Indian goethite-rich iron ore via reduction roasting followed by low-intensity magnetic separation was reported by Ravisankar et al. (2019). They reported that after the magnetic separation and reduction process at 800 °C with 10% coal for 30 min, 90.44% of the 66.58% Fe existed in the ore was recovered. ...
... Sarkar et al. (2016) reported a similar result of a significant weight loss observed over 400 °C which due to the release of the majority of the volatile matters in low-rank coal. Ravisankar et al. (2019) also reported a weight loss of carbon at 500 °C when using non-coking coal as a reducing agent on beneficiation of goethite-rich iron ore. ...
The volume shrinkage and reduction behavior of low-grade iron ore goethite during the solid-state carbothermic process was studied and compared to synthetic goethite. The carbothermic reduction process using low-grade coal as a reducing agent was carried out in the temperature range 1000-1200 °C up to 60 min of reaction time. The results demonstrated that the volume shrinkage, reduction degree, and metallization degree of reduced samples increase with increasing temperature and reaction time. Compared to the reduced samples using synthetic goethite, the volume shrinkage, reduction degree, and metallization degree of the reduced samples using iron ore are lower due to the presence of impurities in Sebuku iron ore concentrates, which include Mg, Mn, Al, and Si. The highest volume shrinkage observed at 1200 °C for 60 min reaction time for the reduced samples using iron ore and synthetic goethite was 63.57±0.57 and 76.51±1.53%, respectively. The observed phases at this point were metallic iron (Fe) and spinel (Fe,Mg)Al2O4. The volume shrinkage of the reduced samples was caused primarily by the weight loss due to carbon, oxygen, and combined water evaporation, as well as the sintering of gangue oxides and metallic iron particles, and partial melting of these phases.
... Magnetic separation techniques are suitable for iron ores having magnetic properties that can be altered through the hydroxyl groups in the iron minerals. In addition, magnetite has high magnetic susceptibility than hematite and goethite [4,6,7]. ...
In this paper, the removal processes for silicon (Si), aluminum (Al) and phosphorus (P) impurities from low-grade iron ore, in which hematite (Fe2O3), goethite (FeO(OH)), and quartz (SiO2) are the main mineral constituents, have been presented. The reverse froth flotation process was applied to remove silicon and aluminum impurities from the iron ore using dodecyltrimethylammonium bromide (DTAB) and dodecylamine acetate (DAA) cationic collectors at a broad slurry pH ranging from 2 to 12. Whereas alkaline roasting followed by a water washing process was employed to remove phosphorus impurity from the iron ore under the various sodium hydroxide concentrations, different roasting temperatures, and prolonged varying times. Results showed that the maximum removal rate of SiO2 and Al2O3 achieved were 58.3% and 31.0% via reverse froth flotation using DTAB collector at pH 12, whereas 38.7% SiO2 and 10.0% Al2O3 with DAA collector. The level of total (SiO2+Al2O3) impurities in the tailing as iron ore product from the reverse flotation was reduced from 7.4 mass% to 4.4 mass% as the initial level. On the other hand, about 61% of phosphorus in the iron ore was removed by the combined alkaline roasting and water washing at the conditions optimized as 50 g/kg-ore NaOH at 300° C for 0.5 h. The grade of phosphorus impurity reached 0.04 mass% from 0.09 mass% (initial grade). Simultaneously, the iron grade and level of SiO2+Al2O3 impurity in the iron ore product from reverse flotation of the low-grade iron ore with DTAB collector reached 60.0 mass% and 4.4 mass%, which are acceptable levels for ironmaking.
