Tielei Tian

To support the production of high-titanium pellets for the gas-based shaft furnace–electric furnace route used to prepare high-titanium feedstock, the phase evolution and structural development of pellets prepared from titanium concentrate, vanadium–titanium powder, and Xuanhua powder were systematically investigated. The results show that the roasting temperature for high-titanium vanadium–titanium pellets should be controlled within 1240–1260 °C. When the titanium concentrate addition is 5 wt%, the pellets exhibit the optimum compressive strength. When the titanium concentrate addition is further increased to 10 wt%, the compressive strength decreases, but the pellets still satisfy the strength requirement for gas-based shaft furnace operation. The addition of titanium concentrate promotes the formation of pseudobrookite, which fills pores and forms crystal-bridge-like bonding with hematite, thereby enhancing pellet consolidation. However, excessive titanium concentrate addition leads to the formation of large amounts of pseudobrookite, which coats hematite grains, suppresses hematite recrystallization, and hinders oxygen diffusion within the pellets. The consolidation of high-titanium vanadium–titanium pellets is dominated by hematite recrystallization and is further strengthened by the intergrowth of hematite with the newly formed Fe₂TiO₅-TiO₂ solid solution, resulting in a denser pellet structure.

The preparation of glass microbeads by gas quenching of blast furnace slag is an effective way to achieve efficient recovery and resource utilization of the residual heat from blast furnace slag. However, due to the high viscosity and easy crystallization of blast furnace slag, there are problems such as low bead formation rate, opaque glass microbeads, and poor chemical stability. MnO tempering agent was developed, and the influence of MnO on the crystallization behavior and rheological properties of the tempered slag was analyzed. The evolution law of the crystallization phase of the tempered slag was clarified, and a viscosity-crystallization coupling control method conducive to the bead formation of blast furnace slag was proposed. The results show that during the isothermal process, when the MnO content in the tempered slag is in the range of 0.17 - 12.24%, with the increase of its content, the initial crystallization temperature and the amount of crystal precipitation gradually decrease, effectively inhibiting the precipitation of crystals. However, when the MnO content exceeds 12.24%, the excessive MnO increases the activity of the easily precipitated phase, and the initial crystallization temperature increases instead. Therefore, when the MnO content in the tempered slag is 12.24%, the crystallization ability is the weakest, and the glass phase content is the highest. In the continuous cooling process, when the MnO content in the tempered slag is 12.24% and the cooling rate exceeds 3 °C/s, the tempered slag completely solidifies into a glassy state.

The forming of rings was a bottleneck of magnesian flux pellets in a rotary kiln, which limited production efficiency. This paper analyses how the coal ash content affects bonding strength and melting behaviour by using magnesian flux pellet powder and coal ash. Also, the mineral phase, microstructure and liquid phase composition of pellet powders that have different coal ash content are analysed in a study. The results show that when the ash content is less than 0.5%, the ash has little influence on the ring-forming material, but when the ash content is more than 0.5%, the ash significantly strengthens the bonding process of the pellet powder. That is, the ash content should not exceed 0.5%. In addition, the consolidation mechanism of the magnesium fluxes spherical ring is mainly solid-phase consolidation. Anorthite and mullite are formed in magnesian flux pellet powders when coal ash is added, resulting in a change in mineral composition. It is worth noting that anorthite exhibits high reactivity with other mineral phases, leading to eutectic reactions. When more coal ash is added, the chemical composition of the mineral phase changes in the briquettes, and the liquid phase exhibits gradual increments in SiO ₂ , MgO and Al ₂ O ₃ content. According to the phase diagram of Fe ₂ O ₃ -CaO-SiO ₂ -3wt%MgO-6wt%Al ₂ O ₃ , the position of the silicate mineral phase shifts towards the high SiO ₂ region, which has the lower temperature. The liquid phase ratio of the briquette increases in this region, ultimately resulting in the formation of rings in the rotary kiln.

Multi-source ferrous metallurgical dust and sludge are significant components of iron-containing solid waste in the iron and steel industry. It is crucial for the sustainable operation of steel enterprises to recycle iron from ferrous metallurgical dust and sludge (FMDS) for use in steel smelting. However, besides Fe, FMDS also contains valuable elements such as Zn, Pb, K, and Na, among others. While these valuable elements hold high recovery value, they impede the direct reuse of FMDS by iron and steel enterprises. This paper introduces the compositional characteristics of multi-source ferrous metallurgical dust and sludge, analyzes the main recycling technologies associated with FMDS at the present stage of development, and discusses the characteristics of different technologies. In view of this, a new idea of the “cooperative treatment of multi-source ferrous metallurgical dust and sludge—full quantitative recovery of valuable elements” is put forward. This new idea integrates a variety of treatment processes to directly recycle FMDS within the steel plant, enhancing the adequacy of dust and sludge recovery and reducing the risk of environmental pollution. This paper provides a reference for achieving the full quantification and utilization of high-value-added FMDS in steel plants.

The silicon content in molten iron is an important indicator, to characterize the temperature of blast furnace (BF) and the quality of molten iron, which is of great significance to the stable operation of large proportion pellets in the BF smelting. Aiming at the problem of poor prediction performance and insufficient accuracy of silicon content, a prediction model of silicon content in molten iron was established based on KMeans++ and improved XGBoost algorithm to divide the information from different BF conditions in the smelting process, The genetic algorithm(GA) was adopted to optimize the model iteratively, which improved the accuracy of the results and reduced the training time for optimal results. The experimental result showed that the prediction hit of the model was improved by clustering the data and reached above 90% on average, and the accurate prediction of silicon content in molten iron in case of a large proportion of pellets of BF smelting was realized.

High-proportion pellet smelting is the direction of optimization of blast furnace burden structures in the future. In this paper, the effect of SiO₂ content on the softening and dropping properties of magnesia flux pellets was studied. And the influence of SiO₂ content on the mineralogical composition and microstructure of magnesia flux pellets was analyzed, which clarified the reason for the air permeability of the middle and lower columns of magnesia flux pellets becoming poor during smelting. The results show that with increasing SiO₂ content, the T₁₀ (softening start temperature) and T_S (melting start temperature) of the column gradually decrease, and the melting range increases; in particular, T₁₀ and Ts decrease dramatically when the SiO₂ content exceeds 6%. The maximum pressure difference increases from 15.0 kPa to 20.7 kPa, and the characteristic value increases from 644.8 kPa·°C to 1334.8 kPa·°C when the SiO₂ content of magnesia flux pellets increases from 6% to 8%. The mineralogical composition difference between low-silica magnesia flux pellets (SiO₂=3.5%) and high-silica magnesia flux pellets (SiO₂=7.0%) at different temperatures is caused by a large amount of unreacted SiO₂ in high-silica magnesia flux pellets. SiO₂ and silicate produce a large amount of liquid phase at low temperature, which reduces T_S. In addition, the dropping temperature of high-silica magnesia flux pellets is higher than that of low-silica magnesia flux pellets. It’s due to the existence of particulate SiO₂ in the primary slag, which causes the slag to become sticky and makes it difficult to separate the slag from iron.

The forming of rings was a key problem of magnesian flux pellets in rotary kiln, which seriously limited production efficiency. Pellet powder and flux were the raw materials of the ring. Based on this, the bonding strength, melting behavior and microstructure of pellet powder and its mixed powder with flux were investigated. The influence of basicity (R = CaO/SiO₂) on ring behavior of pellet powder was analyzed, and ring formation mechanism of magnesian flux pellets was clarified. The results showed that acid pellet powder was not easy to form rings due to lower bonding strength of briquettes. Due to changes in bonding process after mixing of flux, magnesian flux pellet powder produced ferrite and silicate liquid phase with lower melting point, which promoted diffusion and recrystallization of hematite and enhanced compressive strength of briquettes, then finally caused rings to form. Moreover, it is required to control roasting temperature below 1200 °C, which is a necessary condition for magnesian flux pellet powder to form an initial ring which was easy to be destroyed.

The trivalent chromium (Cr) leached from stainless steel slag can be oxidized into hexavalent Cr with strong toxicity in the natural storage process, thus causing severe pollution to the surrounding soil, water, and atmosphere. Currently, the toxicity hazards caused by high Cr concentrations in plants, animals, and humans have attracted widespread attention from across the world. In this study, an overview is presented regarding the occurrence mode, leaching mechanism, and influencing factors for the presence of Cr in the soil of stainless steel slag under natural landfilling conditions. Meanwhile, a summary is made for the research progress in Cr absorption, transport, and accumulation in the soil–plant system. Besides, allowing for the toxicity and detrimental effect of Cr( vi ) in the soil as well as the application of biological and chemical methods for the remediation of Cr( vi )-contaminated soil, a review is conducted on the approach to recycling Cr from stainless steel slag and the application of chemical remediation and biological methods to remedy Cr-containing soil. Finally, a discussion is conducted about the transfer and transformation behavior of Cr in soil–plant system, the practical application of soil remediation technology and the prospect of research in this field.

The forming of rings was a key problem of magnesian flux pellets in rotary kiln, which seriously limited production efficiency. Pellet powder and flux were the raw materials of the ring. Based on this, the bonding strength, melting behavior and microstructure of pellet powder and its mixed powder with flux were investigated. The influence of basicity on ring behavior of pellet powder was analyzed, and ring formation mechanism of magnesian flux pellets was clarified. The results showed that acid pellet powder was not easy to form rings due to lower bonding strength of briquettes. Due to changes in bonding process after mixing of flux, magnesian flux pellet powder produced ferrite and silicate liquid phase with lower melting point, which promoted diffusion and recrystallization of hematite and enhanced compressive strength of briquettes, then finally caused rings to form. Moreover, it is required to control roasting temperature below 1200℃, which is a necessary condition for magnesian flux pellet powder to form an initial ring which was easy to be destroyed.