Producing magnetite concentrate via self-magnetization roasting in N2 atmosphere: Phase and structure transformation, and extraction kinetics

Fluidized Reduction Kinetics of Boron-Bearing Iron Concentrate by Hydrogen at Low Temperatures Based on Model-Fitting and Model-Free Methods

Pyrometallurgy is the most effective way to comprehensively utilize boron-bearing iron concentrate, and there is an urgency for an environmentally friendly and efficient method to achieve the prereduction of boron-bearing iron concentrate. In this study, the mechanism and kinetics of isothermal hydrogen reduction of boron-bearing iron concentrate in a fluidized bed at 500-570 °C were discussed. The reduction degree was quantified in combination with the online gas composition analysis technique, and the phase and microstructure of the reduced products were characterized. The results exhibited that the apparent activation energy remained constant during the whole reduction process, with average values of 50.67 and 48.08 kJ/mol calculated by the model-free and model-fitting methods, respectively, and the reaction was controlled by the contracting sphere model. The formation of a microporous metallic iron facilitated the rapid penetration of hydrogen to the reaction interface. Therefore, the intrinsic chemical reaction at the interface determined the whole reaction process.

Study on Magnetization Roasting Kinetics of High-Iron and Low-Silicon Red Mud

High-iron and low-silicon red mud is not only an alkaline solid waste from Bayer process alumina production, but it is also a very important secondary iron resource. Magnetization roasting is considered as an effective and typical method for the iron recovery and removal of impurities in red mud. In this work, based on the characteristics of large specific surface area and high porosity of red mud, the kinetics of magnetization roasting and phase transformation of red mud were studied. Thermodynamic analysis results show that the reduction of iron oxide in red mud is more easily promoted by CO as reducing agent at low roasting temperature. The reduction reaction is prone to overreduction, and fayalite and ferrospinel can be formed in the reaction system. The phase transformation and iron reduction mechanism during the roasting process were evaluated. Most of hematite and goethite in the red mud decomposed in the process of magnetization roasting, released CO2, and transformed into strongly magnetic magnetite. The reaction process has some characteristics controlled by homogeneous reaction. The process of magnetization roasting reduction with CO was controlled by the hybrid control dynamics model, and the apparent activation energy was 38.31 kJ·mol-1.

Pilot Study on a New Conveyor Bed Magnetization Roasting Process for Efficient Iron Extraction from Low-Grade Siderite

Realizing the large-scale development and utilization of siderite, a difficult iron ore reserve, has great practical significance in ensuring the supply of iron ore resources. Therefore, a new in-house conveyor bed magnetization roasting–dry cooling process was pilot-tested using low-grade siderite from the Daxigou iron ore mine. A two-stage weak magnetic separation method was used for a beneficiation test to investigate the influence of temperature and CO content on the magnetization of siderite. At 600 °C and 800 °C under suspension, iron minerals were converted into magnetite with an effective 3–5 s residence time. Furthermore, at 600 °C and 750 °C, increasing the calcination temperature increased the iron grade and the concentrate recovery rate. However, calcination at temperatures >750 °C resulted in a slight decrease in the iron grade and recovery rate of the concentrate. 61.50% Fe grade and 80.30% concentrate recovery rate were obtained under 750 °C from magnetization roasting. Magnetization roasting in a reducing atmosphere provides mainly magnetite as the roasted ore, and increased CO content can efficiently promote this effect. At 700–780 °C and when the CO content was increased to more than 3 wt.%, the improvement of the roasting effect was very limited. Rapid cooling of the roasted ore using a mixture of circulating exhaust gas and air could prevent considerable oxidation of the magnetic ferrous material. Therefore, the preferred process conditions are 700–780 °C with a CO content range of 1–3%. It provided a concentrate iron grade of 59.27–61.50% and a recovery rate of 78.32–80.30%. The results of this study provide a reference for the development of conveyor bed magnetization technology, process design, and production control.

High-Efficiency Iron Extraction from Low-Grade Siderite via a Conveyor Bed Magnetization Roasting-Magnetic Separation Process: Kinetics Research and Applications

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.

Recovering Iron Concentrate from Low-Grade Siderite Tailings Based on the Process Mineralogy Characteristics

Refractory iron ore is often discarded as tailings. This causes a great waste of iron resources. In this paper, the flash roasting-magnetic separation process was designed by combining the magnetic separation process of magnetite and the process mineralogy of iron tailings. The flash suspension roasting effects with 3–4 s roasting time were evaluated by magnetic separation. The MLA results show that the tailings are ground to a fineness of P90 −75 μm, where the distribution of siderite and M/H in the −75 μm particle size is 85.37% and 92.75%, respectively. Moreover, M/H and siderite are mainly associated with muscovite and quartz. This indicates that regrinding for contiguous bodies of M/H and siderite is beneficial for improving the grade and recovery of iron concentrates. The results of the flash roasting-magnetic separation process show that a mixed iron concentrate containing 60.10% Fe with an iron recovery of 81.13% would be achieved after selective grinding and staged magnetic separation of the roasted ore. The result indicates that the flash suspension roasting effects with 3–4 s roasting time are achievable. The study provides an efficient approach for recovering refractory iron from tailings.