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A new roasting process with a conveying bed was constructed and used to remove sulfur of high-sulfur bauxite. Roasting temperature, phase transformation, microcrystal, specific surface area of high-sulfur bauxite, and the mechanism of the reaction during the roasting process were analyzed. The digestion properties of roasted bauxite were also investigated. The results showed that the sulfur in high-sulfur bauxite can be efficiently removed by roasting in the conveying bed at 520‒720 °C for 2 s. Major reactions of high-sulfur bauxite during roasting were the dehydration of minerals, desulfurization of pyrite, sulfation of SO2, and decomposition of sulfate. The rate of mineral dehydration reaction was significantly slower than that of the desulfurization reaction. The specific surface area of roasted ore greatly increased, and the microcrystal of Al-O mineral was refined, which was conducive to Al2O3 digestion. The mass fraction of sulfide sulfur in high-sulfur bauxite was reduced from 1.20% to 0.01%, and the relative digestibility of alumina reached more than 99% when roasting at 600 °C for 2 s. This paper provides revelations and instructions for the process development and application of high-sulfur bauxite.

Steel is one of the most important industrial materials, which mainly comes from the smelting of iron ore. In view of the huge steel consumption every year, the exploitation of vast reserves of siderite ores is significant for improving the self-sufficiency rate of iron ore resources and ensuring the strategic security of the iron and steel industries. This paper investigated the influence of temperature, time, and other parameters on the magnetic properties of roasted siderite ores using the method of suspended roasting and analyzed the washability of roasted ores under weak-magnetic-field conditions using the magnetic separation tube experiment. The findings of the study explained the iron phase transformation process, i.e., FeCO3 was transformed into Fe3O4 by suspension magnetization roasting. Furthermore, the saturation magnetization of the roasted ore increased in due time at a constant temperature range of 550–750 °C and a roasting time of less than 5 s. It also increased with increasing temperature and constant time. The roasted ore achieved the best magnetic characteristics after roasting at 750 °C for 5 s. After low-intensity magnetic separation, the iron grade of the concentrate changed to 55.12%, with a recovery rate of 90.34%. The study results provide a reference for the development and application of siderite suspension magnetization roasting technology.

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.

The reaction process, mechanism, and kinetics of the desulfurization of high-sulfur bauxite during calcination were investigated using thermal analysis–infrared analysis. A conveyor-bed calcination system was used to study the variations in the physical phase, desulfurization rate, and alumina dissipation rate of high-sulfur bauxite in the range of 500 °C–650 °C. The results show that sclerite monohydrate, kaolinite, rhodochrosite, pyrite, and dolomite mainly decompose during the calcination of high-sulfur bauxite, generating H2O(g), CO2, and SO2 as gaseous products. The decomposition of sclerite monohydrate and kaolinite and the dehydroxylation reactions of rhodochrosite and pyrite occur at <650 °C, with inseparable temperature overlap. High-sulfur bauxite desulfurization follows a three-dimensional spherical diffusion mechanism, with an activation energy of 181.16 kJ/mol, controlled by the diffusion rate of O2 or SO2 through the solid product layer. High-sulfur bauxite was calcined at 600 °C–650 °C for around 3.5 s in a conveyor bed, resulting in a negative divalent sulfur content of <0.03 wt.%, desulfurization rate of >0.98, and relative dissolution rate of alumina of >99%, satisfying the requirements of aluminum extraction via the Bayer method. The desulfurization rate predictions of the kinetic model were consistent with the experimental data.