Improving utilization efficiency of refractory iron ore resources is a common theme for the sustainable development of the world’s steel and iron industry. Magnetization roasting is considered as an effective and typical method for the beneficiation of refractory iron ores. After magnetization roasting, the weakly magnetic iron minerals, including hematite, limonite and siderite, are selectively reduced or oxidized to ferromagnetic magnetite, which is relatively easier to enrich by magnetic separation after liberation pretreatments. The primary magnetization roasting methods include shaft furnace roasting, rotary kiln roasting, fluidized bed roasting, and microwave assisted roasting. This review highlights the developments in magnetization roasting of difficult to treat iron ores, including shaft furnace roasting, rotary kiln roasting, fluidized bed roasting, and microwave assisted roasting in the past decade. Fluidized bed roasting and microwave assisted roasting are considered as the most effective and promising methods, which is essential to be reviewed. Meanwhile, the effective and future magnetization roasting technologies are recommended throughout this review.

The mechanism and kinetics of the reduction of hematite to magnetite in a laboratory-scale, micro-fluidized bed reactor were isothermally investigated. The procedure consisted of the isothermal heating in a flow of a 20%CO–80%CO₂ mixture at temperatures from 500 °C to 600 °C. It was found that the Avrami–Erofe’ev model of nucleation and 1D growth (n = 1.58) successfully described the phase transition of hematite to magnetite, and the value of activation energy ΔE_a of the reaction was estimated to be 48.70 kJ/mol. The microstructure properties for specimens with different conversion degrees were analyzed using the Brunauer, Emmett and Teller (BET) method and scanning electron microscopy (SEM). The results showed that the magnetite nuclei were needle-like, and the hematite specimens became thoroughly porous after complete reduction to magnetite. The physical and chemical processes of the reaction were also discussed.

In this study, a process of magnetizing roasting followed by low-intensity magnetic separation (MR-LMS), which is used to separate and recover iron from a low-grade carbonate-bearing iron ore (containing 34.6 wt.% Fe), was investigated. A magnetic concentrate containing 65.4 wt.% Fe with an iron recovery rate of 92.6 wt.% was obtained under optimal conditions: roasting temperature of 800°C, roasting time of 8 min, bitumite ratio of 10:100, grinding fineness of around 85 wt.% passing 38 µm, and magnetic intensity of 0.12 T. In addition, the phase transformation and magnetic properties were analyzed by X-ray diffraction (XRD) and vibrating sample magnetometry (VSM) to reveal the mechanism.

The size distribution of metallic iron particles is important to better understand the coal-based reduction mechanisms of refractory iron ores. This study was focused on the particle size distribution behavior of metallic iron in coal-based reduction products of an oolitic iron ore. The size of metallic iron particles was measured using image analysis, and the data obtained were analyzed using frequency and cumulative distributions. The curves of the size-frequency distribution and cumulative passing percentage of metallic iron particles exhibited nearly the same trend with respect to particle size. The particle size distribution of metallic iron particles was markedly influenced by both reduction time and temperature. The number of metallic iron particles with large size increased with the reduction time and temperature. Goodness-of-fit tests indicated that the power function and the cumulative distribution function (CDF) of the log-normal distribution best fitted the experimental data of size frequency distribution and cumulative passing percentage of metallic iron particles, respectively.