In last decade, the utilization of CO₂ resources in steelmaking has achieved certain metallurgical effects and the technology is maturing. In this review, we summarized the basic reaction theory of CO₂, the CO₂ conversion, and the change of energy-consumption when CO₂ was introduced in converter steelmaking process. In the CO₂–O₂ mixed injection (COMI) process, the CO₂ conversion ratio can be obtained as high as 80% or more with a control of the CO₂ ratio in mixture gas and the flow rate of CO₂, and the energy is saving and even the energy consumption can be reduced by 145.65 MJ/t under certain operations. In addition, a complete route of CO₂ disposal technology is proposed combining the comparatively mature technologies of CO₂ capture, CO₂ compression, and liquid CO₂ storage to improve the technology of CO₂ utilization. The results are expected to form a large-scale, highly efficient, and valuable method to dispose of CO₂.

To further clarify the dewatering performance and torque evolution during the tailings thickening process, a self-made rake was connected to a rheometer to monitor the shear stress and torque. The dewatering performance of the total tailings was greatly improved to a solid mass fraction of 75.33% in 240 min. The dewatering process could be divided into three stages: the rapid torque growth period, damping torque growth period, and constant torque thickening zone. The machine restart was found to have a significant effect on the rake torque; it could result in rake blockage. Furthermore, the simultaneous evolution of the torque and solid mass fraction of thickened tailings was analyzed. A relationship between the torque and the solid mass fraction was established, which followed a power function. Both the experimental and theoretical results provide a reference for the deep cone thickener design and operation to enhance the dewatering performance.

Rapid flocculation and settlement (FS) of mine tailings is significant for the improvement and development of the filling process, whereas the settlement velocity (SV) of tailings in FS has been recognized as a key parameter to evaluate the settlement effect. However, the influence of temperature on the SV and its mechanism have not been studied. FS experiments on tailings with various ambient temperatures were carried out. The SVs of tailings with a solid waste content of 10wt% and an anionic polyacrylamide content of 20 g·t⁻¹ were measured at different temperatures. The SV presented an “N”-shaped variation curve as the temperature changed from 5 to 40°C. The mechanism of these results can be explained from the perspective of the electric double-layer repulsive force, molecular dynamics, and the polymer flocculation principle, as revealed from the scanning electron microscopy of floc particles. The findings will be beneficial in the design of tailings dewatering processes and save costs in the production of cemented paste backfill.

The microwave-assisted reduction behaviours of two low-grade iron ores having a similar Fe content of 49wt% but distinctly different mineralogical and liberation characteristics were studied. Their performances in terms of the iron grade and recovery as obtained from statistically designed microwave (MW) roasting followed by low-intensity magnetic separation (LIMS) experiments were compared. At respective optimum conditions, the titano-magnetite ore (O1) could yield an iron concentrate of 62.57% Fe grade and 60.01% Fe recovery, while the goethitic ore (O2) could be upgraded to a concentrate of 64.4% Fe grade and 33.3% Fe recovery. Compared with the goethitic ore, the titano-magnetite ore responded better to MW heating. The characterization studies of the feed and roasted products obtained at different power and time conditions using X-ray diffraction, optical microscopy, vibrating-sample magnetometry, and electron-probe microanalysis explain the sequential reduction in the iron oxide phases. Finally, taking advantage of the MW absorbing character of the titano-magnetite ore, a blend of the same with the goethite-rich ore at a weight ratio of 60 : 40 (O2 : O1) was subjected to MW roasting that resulted in a concentrate of 61.57% Fe grade with a Fe recovery of 64.47%.

Magnesium titanate was prepared directly through external coal reduction of seashore titanomagnetite concentrate and magnesium oxide (MgO). The effects of roasting temperature and the type and dosage of reductants on the purity of generated magnesium titanate particles were systematically investigated. Scanning electron microscopy and energy-dispersive spectroscopy analyses were performed to characterize the magnesium titanate particles and observe their purity under different conditions. Results showed that the roasting temperature remarkably influenced the purity of magnesium titanate. At 1200, 1300, and 1400°C, some magnesium ferrite and magnesium aluminate spinel were dissolved in magnesium titanate. However, as the roasting temperature increased to 1500°C, relatively pure magnesium titanate particles were generated because no magnesium ferrite was dissolved in them. The type and dosage of the reductants also remarkably affected the purity of magnesium titanate. The amount of fine metallic iron disseminated in the magnesium titanate particles obviously decreased when lignite was used as a reductant at a dosage of 70wt%. Thus, high-purity magnesium titanate particles formed. At a roasting temperature of 1500°C and with 70wt% lignite, the magnesium titanate product with a yield of 30.63% and an iron content of 3.01wt% was obtained through magnetic separation.

An improved method of (NH₄)₂SO₄ roasting followed by water leaching to utilize zinc oxidized ores was studied. The operating parameters were obtained by investigating the effects of the molar ratio of (NH₄)₂SO₄ to zinc, roasting temperature, and holding time on zinc extraction. The roasting process followed the chemical reaction control mechanism with the apparent activation energy value of 41.74 kJ·mol⁻¹. The transformation of mineral phases in roasting was identified by X-ray diffraction analysis combined with thermogravimetry–differential thermal analysis curves. The water leaching conditions, including the leaching temperature, leaching time, stirring velocity, and liquid-to-solid ratio, were discussed, and the leaching kinetics was studied. The reaction rate was obtained under outer diffusion without product layer control; the values of the apparent activation energy for two stages were 4.12 and 8.19 kJ·mol⁻¹. The maximum zinc extraction ratio reached 96% while the efficiency of iron extraction was approximately 32% under appropriate conditions. This work offers an effective method for the comprehensive use of zinc oxidized ores.

Crystalline rare-earth (RE) carbonates having large particle size were prepared from the lixivium of weathered crust elution-deposited rare-earth ores using the precipitation method with ammonium bicarbonate as the precipitant. Their chemical composition was studied using elemental and thermogravimetric analyses (TGA), and their structure and morphology were characterized using Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The results demonstrate that the crystalline rare-earth carbonate is a hydrated basic carbonate or oxycarbonate and not astable intermediate carbonate in the process of thermal decomposition. The particle size of crystalline rare-earth carbonates with large particle size is in the range of 50–200 μm. With an RE₂O₃ content of up to 95wt%, the quality of crystalline rare-earth carbonates is higher compared to the Chinese National Standard (GB/T 28882–2012). The quality of the product is superior to the Chinese National Standard.

The specific distribution characteristics of inclusions along with the sliver defect were analyzed in detail to explain the formation mechanism of the sliver defect on the automobile exposed panel surface. A quantitative electrolysis method was used to compare and evaluate the three-dimensional morphology, size, composition, quantity, and distribution of inclusions in the defect and non-defect zone of automobile exposed panel. The Al₂O₃ inclusions were observed to be aggregated or chain-like shape along with the sliver defect of about 3–10 μm. The aggregation sections of the Al₂O₃ inclusions are distributed discretely along the rolling direction, with a spacing of 3–7 mm, a length of 6–7 mm, and a width of about 3 mm. The inclusion area part is 0.04%–0.16% with an average value of 0.08%, the inclusion number density is 40 mm⁻² and the inclusion average spacing is 25.13 μm. The inclusion spacing is approximately 40–160 μm, with an average value of 68.76 μm in chain-like inclusion parts. The average area fraction and number density of inclusions in the non-defect region were reduced to about 0.002% and 1–2 mm⁻², respectively, with the inclusion spacing of 400 μm and the size of Al₂O₃ being 1–3 μm.

The effect of three heat processes with different calcium contents on the evolution of inclusions during the ladle furnace refining process of AISI 321 stainless steel was investigated. The size, morphology, and composition of the inclusions were analyzed by scanning electron microscopy and energy-dispersive X-ray spectroscopy. After the addition of aluminum and titanium, the primary oxide in the AISI 321 stainless steel was an Al₂O₃–MgO–TiO_x complex oxide, in which the mass ratio of Al₂O₃/MgO was highly consistent with spinel (MgO·Al₂O₃). After calcium treatment, the calcium content in the oxide increased significantly. Thermodynamic calculations show that when the Ti content was 0.2wt%, the Al and Ca contents were less than 0.10wt% and 0.0005wt%, respectively, which was beneficial for the formation of liquid inclusions in molten steel. Moreover, the modification mechanism of calcium on TiN-wrapped oxides in combination with temperature changes was discussed.

The dilatometric curves of B1500HS high-strength steel at different heating rates were measured by a Gleeble-3800 thermal simulator and analyzed to investigate the effect of heating rate on austenitization. Results show that the value of starting temperature and ending temperature of austenite transformation increase with the rise of heating rates, whereas the temperature interval of austenite formation decreases. The kinetic equation of austenite transformation was solved using the Johnson–Mehl–Avrami model, and the related parameters of the equation were analyzed by the Kissinger method. For those calculations, the activation energy of austenite transformation is 1.01 × 10⁶ J/mol, and the values of kinetic parameters n and ln k₀ are 0.63 and 103.03, respectively. The relationship between the volume fraction of austenite and the heating time at different heating rates could be predicted using the kinetic equation. The predicted and experimental results were compared to verify the accuracy of the kinetic equation. The microstructure etched by different corrosive solutions was analyzed, and the reliability of kinetic equation was further verified from the microscopic perspective.

The influence of welding speed on the joint microstructures of an austenitic stainless steel (ASS) produced by friction stir welding (FSW) was investigated. The FSW process was conducted using a rotational speed of 400 r/min and welding speeds of 50 and 150 mm/min. The study was carried out using electron backscattered diffraction (EBSD) technique in different regions of the resultant stir zones (SZs). The results show that the texture of the advancing side (AS) was mainly composed of

and cube

texture components along with partial

component. Moving from the AS toward the center and the retreating side (RS), the cube texture component disappeared and the

component developed and predominated the other components. Higher welding speed greatly affected and decreased the intensity of the textures in the resultant SZs. Moreover, higher welding speed (lower heat input) resulted in lower frequency of cube texture in the AS.

To simulate the wear and corrosion behavior of high-strength EH47 hull steel in a complicated marine environment in which seawater, sea ice, and sea sand coexist, accelerated wear and corrosion tests were performed in a laboratory setting using a tribometer. The effect of large loads on the behavior of abrasion and corrosion in a 3.5wt% NaCl solution with ice and sand to simulate a marine environment were investigated. The experimental results showed that the coefficient of friction (COF) decreases with increasing working load; meanwhile, the loading force and sand on the disk strongly influence the COF. The mechanisms of friction and the coupling effect of abrasion and corrosion in the 3.5wt% NaCl solution with sand were the wear and corrosion mechanisms; furthermore, the wear mechanism exerted the predominant effect.

This study investigated the hot corrosion performance of a dissimilar weldment of Ni-based superalloy and stainless steel joined by CO₂-laser welding and improved by high-velocity oxy-fuel (HVOF) coating in a Na₂SO₄−60wt%V₂O₅ environment at 900°C. A dissimilar butt joint of AISI 321 and alloy 825 was fabricated by CO₂-laser welding with low heat input after obtaining the optimum welding parameters by bead-on-plate trials. The metallurgical and mechanical properties of the laser weldment were evaluated. The tensile test results indicated the occurrence of fracture in the base metal AISI 321 side. The HVOF process was employed to coat Ni−20wt%Cr on the weldment. To evaluate the surface morphology of the corrosion products formed on the uncoated and Ni−20wt%Cr-coated weldments, scanning electron microscopy (SEM) analysis was performed. Energy-dispersive spectroscopy (EDS) was used to determine the different elements present on the surface scales. The existence of oxide phases on the weldments was determined by X-ray diffraction (XRD). The cross sections of the weldments were characterized by SEM with EDS line mapping analysis. The results indicated that the Ni−20wt%Cr-coated weldment exhibited superior hot corrosion resistance due to the development of Cr₂O₃ and NiCr₂O₄ protective oxide scales.