Mo-Si compound-based ultrahigh temperature structural material (UHTM) is a new high-temperature structural material with great potential due to its high melting point, high hardness, and suitable density. As an important material to meet the demands of advanced high-temperature structural applications in the range 1200–1600 °C, in oxidizing and aggressive environments, it has attracted the attention of researchers in aerospace, energy, chemical industry, machinery, mechanical metallurgy, and other fields. This study could provide a reference for the research and application of Mo-Si intermetallic compounds as UHTMs. Based on their crystal structure and properties, we summarized the preparation, limitations, and modification methods of Mo-Si intermetallic compounds and reviewed the research progress in their toughness reinforcement and medium-temperature resistance improvement. Based on the literature review, there has been a certain level of progress in the research on modification of Mo-Si intermetallic compounds worldwide. However, both the high brittleness at room temperature and insufficient strength at high temperature have not been solved yet.

Basic oxygen furnace (BOF) slag contains a significant amount of iron-containing species, which is considered to be iron resources and therefore need to be recovered. In this work, the oxidation behaviour of BOF slag under air (at selected oxidation temperatures and holding time) was investigated to explore the potential of transforming non-magnetic wustite in the BOF slag into magnetic spinel, which may subsequently be recovered by magnetic separation. The experimental results show that the iron-containing spices in the BOF slag can be oxidised into magnetic spinel phases in the investigated temperature range of 1000–1150°C and thereafter be recovered by magnetic separation. The formation of these phases is closely related to the oxidation temperatures and holding time: a higher oxidation temperature and longer holding time lead to a larger amount of formed magnetic species; however, the amount of formed magnetic species decreases at elevated temperature (>1050°C) and with extended holding time (>40 min).

Although steel slag exhibits cementitious properties, the addition of steel slag in cement is still limited due to both the presence of excess iron oxides and instability of free lime and periclase. This paper proposes a method for oxidizing molten slag in air, aiming at extraction of superfluous wustite and stabilization of free lime and periclase. Mineralogical characteristics of raw slag and modified products were examined using X-ray diffraction (XRD), scanning electron microscopy equipped with backscattered electron imaging (SEM-BEI), energy dispersive spectrometry (EDS) and thermogravimetric analysis (TGA) with differential scanning calorimetry (DSC). Thermodynamic calculations were performed to aid to discuss the experimental results. The results indicate that non-magnetic wustite and periclase are transformed into magnetic spinel (magnetite/magnesioferrite) after oxidation. Temperature has a significant effect on the formation of spinel. The mass fraction of free lime decreases from 3.54 wt.% to 0.96 wt.% as a result of the conversion from free lime to calcium ferrite.

Metallurgical industries often discharge slag containing valuable elements that are poorly utilized when producing copper alloys and silicon-manganese alloys. To improve the utilization rate, in this study, a method to mix copper slag with water-quenched silicon-manganese slag and CaO for roasting and modification was proposed. In this work, FactSage 8.0, DSC-TG, and XRD were used to examine the phase change during the modification process and investigate the impacts of the CaO content, roasting temperature, and holding time on the modification effect. The results showed that the addition of water-quenched silicon-manganese slag and CaO could effectively promote the transformation of fayalite to (Mn, Mg, Fe)Fe2O4, with the highest conversion rate occurring at a 10% CaO content. An increase in the temperature and prolongation of the time facilitated fayalite transformation, but excessive temperature or time could result in iron loss. The optimal recovery rate and iron grade were achieved with roasting at 1400 °C for 60 min. This method can provide a concentrate suitable for producing copper-containing antibacterial stainless steel and wear-resistant cast iron, and the tailings can be used to produce ceramic materials.

Significant amounts of smelting slag are generated during the production of steel, refined copper, and refined magnesium. These slags contain abundant valuable metallic elements, such as Fe, Cu, Zn, Co, and Mg, that have not been fully utilized in the past. This study proposes a method for modifying copper slag by mixing it with steel slag and magnesium slag, followed by roasting with additions of Fe₂O₃ and MgO. The samples were roasted at 1400 °C for 30 min, cooled to 1000 °C at 1.5 °C/min, and then water-quenched to room temperature. Phase transformations during modification were analyzed using FactSage 8.0, DSC–TG, and XRD. The effects of factors such as the content of Fe₂O₃ and MgO on the modification efficiency were investigated. The results indicate that, under the condition of maintaining a steel slag: copper slag: magnesium slag ratio of 37:37:26 and adjusting the basicity (CaO/SiO₂ ratio) with CaO to 2.0, the addition of Fe₂O₃ and MgO promotes the formation of spinel. However, excessively high contents of Fe₂O₃ and MgO lead to refinement of the spinel grains and reduce the iron grade of the concentrate. Within the investigated composition range, the samples with total Fe₂O₃ and MgO contents of 27.66 wt% and 7.56 wt%, respectively, showed the best magnetic separation performance among the tested compositions. Through magnetic separation, the concentrate has good economic and industrial application value in industries such as steelmaking and powder metallurgy, while the tailings can be utilized as raw materials for manufacturing ceramics, glass–ceramics, cement, and concrete.

Steel, copper, and magnesium slags are typical metallurgical solid wastes containing potentially recoverable Fe, Ca, Mg, and Si. Copper slag is relatively rich in iron, but much of this iron is bound in fayalite or Fe–Mg olivine, which limits direct recovery by magnetic separation. Steel slag contains substantial CaO, MgO, and iron oxides, whereas magnesium slag is rich in CaO and also contains MgO; together, they can supply the alkaline and Mg-bearing components required for the phase reconstruction of iron-bearing silicates. The compositional complementarity of the three slags therefore provides a basis for iron recovery and the controlled conversion of non-magnetic constituents. In this study, steel, copper, and magnesium slags were mixed at a mass ratio of 37:37:26. CaO was added to regulate the basicity and promote the redistribution of Fe from olivine-type silicates into magnetically recoverable spinel-group phases. The effects of CaO addition and the combined water-quenching onset temperature/slow-cooling duration on phase transformation, microstructure, and iron recovery were investigated. The samples were held at 1400 °C for 30 min, cooled at 1.5 °C min⁻¹, and water quenching was initiated at 1300, 1200, 1100, or 1000 °C. The results showed that an appropriate CaO dosage promoted the conversion of Fe–Mg olivine toward Ca₂SiO₄ and Fe- or Mg-bearing oxide phases, whereas excessive CaO favored calcium-ferrite formation. Among the S1–S4 samples, S3, with a basicity of 2.0, showed the highest mean concentrate yield and iron recovery, yielding a concentrate with a T. Fe grade of 19.02% and an iron recovery of 90.89%. In the T1–T4 experiments conducted using S4, lowering the water-quenching onset temperature necessarily extended the slow-cooling duration and was associated with changes in spinel morphology and magnetic-separation performance. The particle-area distribution changed non-monotonically from T1 to T3, whereas T4 exhibited pronounced aggregation into larger blocky spinel domains and showed the highest mean T. Fe grade and iron recovery in this series. When water quenching was initiated at 1000 °C, the concentrate T. Fe grade and iron recovery reached 20.75% and 94.86%, respectively. Within the fixed three-slag ratio and investigated parameter ranges, CaO addition and cooling history affected phase redistribution and magnetic separation, although the resulting magnetic products showed only limited iron enrichment.