The effects of SiO₂ content on the compressive strength, reduction behavior and melting-dripping properties of the pellets were investigated under experimental conditions. The experimental results indicated that the compressive strength of pellets gradually decreased with increasing SiO₂ content, mainly because the pellets with high SiO₂ had poor crystallization capacity, a more liquid phase and more pores. With increasing SiO₂ content from 2.19 wt% to 8.13 wt%, the reduction degree of pellets descreased due to the generation of 2FeO·SiO₂. Based on the morphology analysis, inside of the pellets, 2FeO·SiO₂ caused the compact structure and fewer microspores with increasing SiO₂ content, which was unfavorable for the reduction process and resulted in the decrease of the reduction degree. Also, increasing the SiO₂ content had negative effects on the melting-dripping properties of pellets. The melting-dripping properties can be improved by adding some sinter with high basicity in the mixed burden. The current work established the relation between SiO₂ content and reduction-melting behavior of pellets, which can provide theoretical and technical support for the effective utilization of pellets with different SiO₂ content in blast furnace process.

This work presents a semi-smelting reduction and magnetic separation process for the recovery of iron and alumina slag from iron rich bauxite ore. The effect of the process parameters on the recovery rate of iron, maximum particle size of the iron nugget, and the Al₂O₃ content of the alumina slag was investigated and optimized. The results show that the iron nuggets and alumina slag can be obtained in a short time through a semi-smelting reduction and magnetic separation process. The maximum particle size of iron nugget is about 15 mm, and the recovery rate of the iron and Al₂O₃ grade of the alumina slag are 96.84 wt % and 43.98 wt %, respectively. The alumina slag consisted mainly of alumina (α-Al₂O₃), calcium hexaluminate (CaAl₁₂O₁₉), gehlenite (Ca₂Al₂SiO₇), and small amounts of hercynite (FeAl₄O₇), and metallic iron (M.Fe).

Adding MgO to sinter is considered to be a popular counter measure to cope with the use of high Al₂O₃ ores. The purpose of this paper is to investigate the effect of the MgO content on the reduction melting behavior in order to clarify the main mechanism of melting and dripping under simulated blast furnace (BF) conditions. It was found that reduction behavior was inhibited with an increased MgO content; the reduction mechanism was further investigated by means of XRD, SEM, and kinetic analysis. The influence of MgO on the melting mechanism of high basicity sinter was also studied. The softening start temperature and softening temperature increased, and the softening zone increased as a whole with the increased MgO contents from 1.3 to 2.0 wt%. The melting temperature was similar, because the MgO remained in an unslagged state and existed in wustite as FeO-MgO solid solution. The dripping temperature was increased; the main reason for this was that high melting-point slags appeared, and that it was more difficult for carburization to occur with increased MgO content. The most appropriate MgO content in the sinter was 1.3 wt% according to principal component analysis (PCA).

With the gradual depletion of high-quality iron-ore resources, ironmaking blast furnaces have gradually shifted to using high-content Al₂O₃ iron ore. Under this condition, the addition of MgO in the slag is adopted to alleviate operation problems caused by the high content of Al₂O₃. However, the proper value of the MgO/Al₂O₃ ratio for blast-furnace slag systems (Al₂O₃ = 8–25%) is not systematically studied. In this paper, we discuss the proper MgO/Al₂O₃ ratio on the basis of blast-furnace slag systems under different Al₂O₃ contents. On the basis of thermodynamics and phase-diagram analysis, it could be concluded that: (1) the MgO/Al₂O₃ ratio is not limited when Al₂O₃ in slag is less than 14%, (2) the MgO/Al₂O₃ ratio is required to be in the range of 0.40–0.50 when Al₂O₃ in the slag is 15–17%, and (3) the MgO/Al₂O₃ ratio should be 0.45–0.55 when Al₂O₃ in the slag is larger than 18%. The proper MgO/Al₂O₃ ratio value has been established in various industries, and it has achieved significant economic and social benefits.

With a view to satisfying the requirements of environmental protest and efficient usage of resources, a novel process for efficiently extracting vanadium (V), titanium (Ti), and iron (Fe) from vanadium-bearing titanomagnetite concentrate was developed. In the new process, vanadium is pre-extracted by additive-free roasting under the air atmosphere and alkaline leaching technologies. In this paper, transformation of vanadium-bearing titanomagnetite concentrate in the roasting is investigated based on thermodynamic analyses and experimental discussion. Thermodynamic analyses show that oxidation of V(III) into V(V) would happen in the roasting experiment over the range of 327–1327 °C and vanadium-iron spinel phase (FeV₂O₄) can be oxidized more easily than magnetite (Fe₃O₄) when the temperature is higher than 861 °C. Experimental results show that some compounds (V₂O₅, Fe₂Al₄Si₅O₁₈, and Fe₂SiO₄) with low melting temperature were obtained by solid reactions at low temperature and melted as a binding phase at elevated temperature. Liquids were generated due to some chemical reactions or phase transformation reaction (Fe₂V₂O₄(s) → Fe₂O₃(s) + liquid) at elevated temperature. Main phases of Fe₂O₃ and Fe₂TiO₅ are connected and sintered with the binding phases of the compounds with low melting temperature or the mixtures with low liquidus temperature. In addition, higher roasting temperature leads to higher vanadium leaching efficiency over the range of 800–1200 °C. However, over-burning would happen at 1250 °C, some of vanadium oxide was wrapped by silicate network, and the conversion of V(III) into V(V) was prevented from occurring. Therefore, the vanadium leaching efficiency decreased from 59.1% (T_roa. = 1200 °C) to 57% (T_roa. = 1250 °C).