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The Bayan Obo ore deposit is a world-renowned polymetallic coexistence mine that integrates important elements, such as rare earths, iron, niobium, and titanium. The chemical properties of niobium and titanium are similar, and the two often coexist in the Bayan Obo deposit as isomorphs, making them difficult to separate. Therefore, the separation of niobium and titanium is crucial for the efficient utilization of niobium resources in the Bayan Obo ore deposit of China. To discuss the feasibility of separating niobium and titanium by selective electrolysis, cyclic voltammetry and square wave voltammetry were used to study the reduction mechanism of niobium oxide and titanium oxide in NaF–Na3AlF6 molten salt. The results revealed significant differences in the diffusion coefficients and reduction steps of Nb5+ and Ti4+ during reduction at a molybdenum cathode. At 950 °C, the diffusion coefficient of Nb5+ during reduction at a molybdenum cathode was 3.57 × 10–6 cm2/s. Also, in the NaF–Na3AlF6 system, Nb5+ underwent a three-step reduction as follows: Nb(V)→Nb(IV)→Nb(I)→Nb. The diffusion coefficient of Ti4+ during reduction at the molybdenum cathode was 9.92 × 10–7 cm2/s, and Ti4+ underwent a two-step reduction in the NaF–Na3AlF6 system: Ti(IV)→Ti(I)→Ti. When Nb2O5 and TiO2 were both present in the NaF–Na3AlF6 system, the deposition potential of niobium metal (−0.64 V) differed from that of titanium metal (−0.77 V). These differences in diffusion coefficient, reduction step, and deposition potential enabled selective electrolytic separation of niobium and titanium.

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Phase equilibria in the CaO-La2O3-Nb2O5 system are of great significance for the utilization and application of rare earth and Nb resources. In the present work, the phase equilibria in high w(Nb2O5) corner of the CaO-La2O3-Nb2O5 system were studied by high-temperature equilibrium and quenching technology. Based on the continuity of phase diagram, a “Concavity and Convexity Rule” was proposed to predict the reasonable range of the unknown liquidus line. Finally, the isothermal sections and liquidus projection of the CaO-La2O3-Nb2O5 phase diagram were constructed, which include the primary phase fields of CaNb2O6, LaNbO4, Ca2Nb2O7, (Ca, Nb, La)O, and related liquidus lines at 1823, 1773, and 1673 K. Moreover, the subsolidus phase field of (Ca, Nb, La)O-LaNbO4-Ca2Nb2O7 with peritectic nonvariant reaction and CaNb2O6-LaNbO4-Ca2Nb2O7 with eutectic nonvariant reaction were determined, respectively.

The effect of the addition of B2O3 and the CaO/Al2O3 ratios on the CaO–Al2O3–B2O3 melts’ structure was fully analyzed by molecular dynamics (MD) simulations. The results show that, with the increase in CaO/Al2O3 ratios, the charge compensation for [AlO4]5− tetrahedron changed from the oxygen tricluster structure to the charge provided by Ca2+, and the structure of [AlO4]5− tetrahedron was stabilized. The addition of B2O3 reduced the degree of polymerization of the aluminate melt, which, in turn, lowered the melt viscosity; in the systems with CaO/Al2O3 mole ratio less than 1, the added B2O3 mainly existed in the form of [BO3]3−, which reduced the symmetry and the strength of the melt network structures; in the higher CaO/Al2O3 ratio systems, the depolymerization ability of the addition of B2O3 on aluminate network structures was enhanced with the increase in CaO/Al2O3 ratios, and the overall degree of polymerization of the melt decreased. The viscosity measurement shows that B2O3 lowers the viscosity of CaO–Al2O3 melts, which was consistent with the results predicted by MD simulations.

In the current work, the phase equilibria of CaO-SiO2-La2O3-Nb2O5 system at 1200 °C in reducing atmosphere (PO2 = 10−15 atm) was investigated according to the melting separation process for extracting lanthanum and niobium resources from Bayan Obo tailing. High temperature equilibrium experiment, scanning electron microscope, and energy dispersive spectrometer (SEM-EDS) were used to determine the compositions of equilibrium phases. According to the experiment results, the phase equilibria of the CaO-SiO2-La2O3-Nb2O5 system in reducing atmosphere were ascertained and the 1200 °C isothermal phase diagram of CaO-SiO2-La2O3-Nb2O5 system in reducing atmosphere was constructed. The research results not only play an important role in guiding the development of the lanthanum and niobium extraction process, but also enrich the thermodynamic data of relevant silicate slag systems.

It is of great economic, environmental and social benefit to discover harmless treatment and resource utilization options for spent lithium-ion batteries (LIBs), which contain a large proportion of valuable metal elements (e.g., Li, Ni, Co, Mn, Cu, and Al) and poisonous chemicals (e.g., lithium hexafluorophosphate and polyvinylidene fluoride). The present work summarized the leading technologies and hot issues in the disposal of spent LIBs from new energy vehicles. Moreover, development of the trend of innovative technologies for the recycling of spent LIBs is recommended.

The process of granulation in blast furnace slag (BFS) by gas quenching can effectively recover the waste heat of BFS and improve the value-added nature of the BFS byproduct. With decreasing temperature, BFS crystallizes into melilite, anorthite, spinel, etc. Mineral crystallization, however, is not conducive to the production of amorphous BFS beads. This study uses thermodynamic simulation and remelting experiments to study the influences of basicity, acidity, and the MgO and Al2O3 content of the BFS on the crystallization. By controlling the composition of the BFS, mineral crystallization in the process of granulation in BFS, by gas quenching, could be prevented. The results show that increasing the basicity of the BFS causes the mineral crystallization temperature to increase rapidly. The mineral phase then crystallizes at a higher temperature, which is not conducive to the formation of an amorphous phase. Increasing the acidity of the BFS can greatly decrease the crystallization temperature, e.g., when the acidity increases to 1.3, amorphous BFS beads can be obtained at the gas quenching temperature (1623 K). Although increasing the MgO and Al2O3 contents in the BFS had little effect on the crystallization temperature and yield, the preparation of amorphous BFS beads by gas quenching could be realized by adjusting the acidity of the BFS.

Mold electromagnetic stirring (M-EMS) has been widely used in many continuous casters. In order to have a deep insight into the collision-coalescence among inclusions under M-EMS by a Eulerian approach, the effects of Archimedes electromagnetic force on the inclusion are expressed by three-dimensional Archimedes electromagnetic slipping velocity and Archimedes electromagnetic collision. Numerical results show that a turbulent collision is the most important factor to cause inclusions to collide with each other, Archimedes electromagnetic collision has a minor effect, Stokes collision is the third factor, and Brownian can be ignored. In the case of M-EMS, there are two recirculation zones above and below the M-EMS central cross-section, and the inclusion spatial distributions have the inverted U-shape.

Sulfuric acid-based leaching is a promising cleaner method to produce chromium salts, but its feasibility for treating low Fe(II)-chromite still remains to be proven. A Box–Behnken design (BBD)-based set of experiments for sulfuric acid leaching of low Fe(II)-chromite was utilized in this work for generating an experimental dataset for revealing the functional relationships between the processing parameters and the extraction yields of Cr and Fe. The dependent variables were found to exhibit strong intercorrelations and the models developed on the basis of statistical criteria showed excellent prediction accuracy. The optimum process conditions of leaching treatment were found to be a temperature of 176 °C, a dichromic acid/chromite mass ratio of 0.12, and a sulfuric acid concentration of 81%. Furthermore, the dissolution behavior of chromite in the leaching process and the effect of dichromic acid were experimentally investigated. It was found that the decomposition efficiency was highly dependent on the Fe(II) content of chromite, and that the dichromic acid acted both as an oxidant and a catalyst in the leaching process. On the basis of the results of this study, a novel process for treating low-Fe(II) chromite was proposed.

The Al2O3-SiO2, La2O3-Al2O3, and La2O3-SiO2 binary phase diagrams were estimated by Redlich−Kister expression. La4.67Si3O13 (=La4.67(SiO4)3O) was introduced to improve the existing phase diagrams. The Al2O3-SiO2-La2O3 ternary phase diagram extrapolated by Kohler method was optimized. Then, the liquidus of Al2O3-SiO2-La2O3 system at 1600 °C was compared with Al2O3-SiO2-RE2O3 (RE = Rare Earth Elements) systems and experimental results in other literature. The high temperature experiments were conducted in the tube furnace at 1500 °C. Then the field emission scanning electron microscope (FE-SEM), energy dispersive spectrometer (EDS), and X-ray diffraction (XRD) were employed to verify the calculated liquid region and precipitates phase at 1500 °C. Moreover, the liquidus of binary systems were compared with FactSage results and experiments. The optimized ternary phase diagram shows the relatively reliable region of liquid phase, and it is significant to the seal glass of solid oxide fuel cells and other fields being related to RE containing silicates.

Ce-doped nano-α-Fe2O3 was successfully synthesized via the hydrothermal method. The properties of the prepared particles were studied by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS) and electrochemical methods. It was found that the Ce element can be doped into the α-Fe2O3 lattice resulting in lattice distortion, which can refine the grain and improve the crystal surface’s integrity significantly. In addition, doping of Ce element can shorten the Fe−O bond length in the α-Fe2O3 crystal, cause a blue shift of the stretching vibration band, enhance binding energy of Fe−O and the chemical stability of the α-Fe2O3 crystal.

To characterize the splashing behavior under the impact of the top-blown gas jet in converter, in this paper a physical model is developed with the prototype of a 200 t converter in China. We captured the impact cavity morphology triggered by the top-blown gas jet of the oxygen lance, and found that the impact cavity shape gradually changed following the sequence of “disc„ → “bowl„ → “cone„ with the increase in the gas flow, leading to the variation of the splashing modes. Moreover, the splashing inside and outside the converter was characterized quantitatively under the different top-blown gas jet conditions. The results showed that the splashing on the furnace inner wall concentrated at the region adjacent to the molten bath surface, implying severe flushing of the furnace lining of this region. The critical gas flow of splashing outside the converter is 32.3 Nm3·h−1, corresponding to a gas flow of 39,000 Nm3·h−1 in the prototype. In addition, the foaming slag can suppress the splashing during the smelting process. The statistics of the splashing flux provide a reference for maintaining the safety of the workers and the converter equipment.

To solve the nozzle clogging issue in the continuous casting process of 253MA steel, a method of modifying solid inclusions to liquid phases is proposed. The CALPHAD technique was employed to predict the liquid region of the Al2O3-SiO2-Ce2O3 system. Then a thermodynamic package based on the extracted data during the phase diagram optimization process was developed. This package was then used to compute the appropriate aluminum addition, which was 0.01% in 253MA steel. The Si-Al alloy was chosen as the deoxidant according to the thermodynamic analysis. The solid inclusions were ultimately modified to liquid phases at 1500 °C when cerium was added through the equilibrium experiments in a MoSi2 tube furnace.

The chromium elution behavior of stainless steel (SS) slag depends highly on the chromium distribution, and the molten modification process proved to effectively improve the chromium enrichment in stable phases. However, the phase transformation and variation of chromium stability during the subsequent cooling process is still poorly understood. In this work, the phase composition and chromium distribution of SS slag from different quenching temperatures were experimentally studied, and the stability of chromium-bearing phases was evaluated using standard leaching tests. The results indicated that dicalcium silicate and spinel phases had formed in the molten slag at 1600 °C, while the dicalcium silicate disappeared and the phases of merwinite and melilite precipitated when the temperature decreased from 1600 to 1300 °C (at a rate of 5 °C/min). During this cooling process, the chromium migrated from other phases into the spinel, significantly suppressing the chromium elution. The leaching results also demonstrated that the potential chromium-bearing phases of glass, dicalcium silicate and merwinite are unstable and are presumably the main source of chromium release. The treated SS slag meets the requirements for the utilization of chromium-bearing slag in the cement and brick industries.

The stabilization of chromium is of great importance to the use of stainless steel slag (SSS), and the influence of lime on the stability of chromium is currently unclear. In this work, the variation of phase transformation and chromium distribution with slag basicity (CaO/SiO2) were investigated experimentally, and the leaching ability of chromium was evaluated. Results showed that chromium-bearing phases were glass, dicalcium silicate (C2S), spinel, and periclase, while the degree of enrichment of chromium in these phases was found to be closely related to the basicity. The optimal basicity obtained in this research was 1.5, with the chromium mainly present in the stable spinel and exhibiting the lowest leaching ability. The product layer structure of unmelted lime was studied as well, showing a periclase layer and a Ca2SiO4 layer. Some CaCr2O4 had formed in the periclase layer, which is potentially hazardous for the environment and living organisms.

To release the environmental pressure from the massive discharge of bauxite residue (red mud), a novel recycling method of red mud in steel making process was investigated through high-temperature experiments and thermodynamic analysis. The results showed that after the reduction roasting of the carbon-bearing red mud pellets at 1100–1200 °C for 12–20 min, the metallic pellets were obtained with the metallization ratio of ≥88%. Then, the separation of slag and iron achieved from the metallic pellets at 1550 °C, after composition adjustment targeting the primary crystal region of the 12CaO·7Al2O3 phase. After iron removal and composition adjustment, the smelting-separation slag had good smelting performance and desulfurization capability, which meets the demand of sulfurization flux in steel making process. The pig iron quality meets the requirements of the high-quality raw material for steel making. In virtue of the huge scale and output of steel industry, the large-scale consumption and zero-waste recycling method of red mud was proposed, which comprised of the carbon-bearing red mud pellets roasting in the rotary hearth furnace and smelting separation in the electric arc furnace after composition adjustment.

The sodium salt roasting process was widely used for extracting vanadium due to its high yield rate of vanadium. However, the serious pollution was a problem. The calcium roasting process was environmentally friendly, but the yield rate of vanadium was relatively lower. Focusing on the calcium metavanadate produced in the calcium roasting process of vanadium minerals, the mechanism of the carbonate leaching for calcium metavanadate and its leaching kinetics of calcium metavanadate were studied. With the increase of the leaching agent content, the decrease of the particle size, the increase of the temperature and the increase of the reaction time, the leaching rate of vanadium increased, and the constant of reaction rate increased. In the carbonate leaching process, the calcium carbonate was globular and attached to the surface of calcium metavanadate. In the solution containing bicarbonate radical, lots of cracks formed in the dissolution process. However, the cracks were relatively fewer in the solution containing carbonate. In the present study, the carbonate leaching for calcium metavanadate was controlled by diffusion, the activation energy reached maximum and minimum in the sodium bicarbonate and the sodium carbonate solution, respectively. The activation energy value in the ammonium bicarbonate solution was between those two solutions. The kinetic equations of the carbonate leaching for calcium metavanadate were as follows: 1 − 2/3η − (1 − η)2/3 = 4.39[Na2CO3]0.75/r0 × exp(−2527.06/T)t; 1 − 2/3η − (1 − η)2/3 = 7.89[NaHCO3]0.53/r0 × exp(−2530.67/T)t; 1 − 2/3η − (1 − η)2/3 = 6.78[NH4HCO3]0.69/r0 × exp(−2459.71/T)t.

Because of the acute toxicity of Cr(VI)-bearing substances, the pollution problem caused by chromite process residue has become a worldwide concern. In the view of relevant studies, the technologies based on the alkali treatment cannot fundamentally resolve the pollution problem, because the oxidation of Cr(III) to Cr(VI) is unavoidable during chromite decomposition. In contrast, the oxidation of Cr(III) to Cr(VI) can be controlled by the sulfuric acid treatment of chromite, and the Cr(VI) pollution can be eliminated from the original source of production. Many research studies focusing on the resolutions of the key obstacles hindering the development of the sulfuric acid treatment process have been carried out, and significant progress has been achieved. In this study, a clean hydrometallurgical process without the generation of hexavalent chromium is demonstrated. First, the chromite was decomposed and leached by sulfuric acid solution in the presence of an oxidant. Then, iron was hydrothermally removed from the acid solution as the precipitate of jarosite. Finally, chromium salts were obtained by adjusting the basicity of the solution, separation and drying. With the aim of realizing industrialization, future research emphasis on the development of the sulfuric acid treatment process is proposed in this study.