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The rare earth minerals in Bayan Obo are poor, fine, scattered and variegated, so it is very difficult to achieve efficient separation. Superconducting magnetic separation technology is an efficient separation technology for refractory minerals. In this paper, the magnetic field induced by a matrix in a superconducting magnetic field is studied based on a finite element method and a separate numerical calculation method, and a model for the trajectories of rare earth mineral particles in Bayan Obo is obtained. The matching relationship between the matrix parameters and the capture radius is obtained through model calculation, as is the optimal capture radius and capture efficiency. The results show that the magnetic field gradient and magnetic field force decrease with increasing distance from the surface of the matrix and that the critical distance of the magnetic field induced by the matrix is 1.5 times the diameter of the matrix. The particle capture radius and capture efficiency are inversely proportional to the matrix diameter. When the matrix diameter is 0.06 mm, the capture efficiency is higher than at other diameters. The theoretical capture efficiency of rare earth mineral particles of size 20–38 µm is approximately 98%, but for particles below 10 µm, the capture efficiency is only 30%. The research results provide a quantitative selective capture law for the matrix diameter and particle diameter, which provides theoretical guidance for production practice. [ABSTRACT FROM AUTHOR]

NbC particle reinforced copper matrix composites with 1%, 2%, 3% and 4% NbC were prepared via microwave sintering using niobium carbide particles and electrolytic copper powder as raw materials. The effects of niobium carbide mass fraction and microwave sintering temperature on the properties of copper matrix composites were investigated by observing the microstructure and testing the density, hardness, and conductivity. The results show that the NbC particles in the copper matrix can be evenly distributed on the matrix except for a small amount of particles that agglomerate and grow up; with the increase of sintering temperature, the density, conductivity and hardness of copper matrix composites increased: the density increased from 5.8 g/cm³ to 7.208 g/cm³ ; the conductivity increased from less than 10% IACS to 63.8% IACS. The hardness increased from 35 HV to 64.5 HV. With the increase of the mass fraction of the reinforced phase, the hardness increased from 36 HV to 64.5 HV at 1 000 °C, the density decreased from 7.208 g/cm³ to 5.86 g/cm³, and the conductivity decreased from 63.8% IACS to 24.1% IACS. When the mass fraction of NbC is 1%, the influence of sintering temperature is obvious. When the sintering temperature is 1 000 °C, the conductivity reaches the maximum, which is 63.8% IACS. [ABSTRACT FROM AUTHOR]

In recent years, the preparation of CMAS nanocrystalline glass-ceramics has shown potential as an application of secondary resourcing technology in utilizing Bayan Obo iron ore tailings containing rare earth elements. The crystallization mechanism for nanodiopside-type glass-ceramics was studied via an investigation of the nonisothermal crystallization kinetics of the glass system, combined with the in situ observation of softening and crystallization of the basic glass using a high-temperature laser confocal microscope. The results show that the activation energy of nucleation in the glass system is higher than that of crystal growth by using the Ozawa model. The crystallization mechanism changes as the crystallization fraction increases, that is, from the three-dimensional growth in which the nucleation rate increases with time in an interface-controlled manner (a > 1, b = 1, m = 3) at the initial stage of crystallization to a decreased nucleation rate in a diffusion-controlled growth (a = 0.5, b = 0.5, m = 3) at the middle and later stages. This process involves both surface crystallization and volume crystallization. The crystallization was observed in situ, and it was further confirmed that there exists a critical nucleation temperature between T g and T x , which is related to the interface free energy and critical Gibbs free energy difference. When the temperature exceeds the critical value of T g + 55 K, the system begins to exhibit visible crystallization. With an increase in temperature, the basic glass softened considerably, while the crystal grew significantly. In addition, the surface roughness can be used to characterize the crystallization process, providing a new research method for crystal growth. [ABSTRACT FROM AUTHOR]

A population-based metaheuristic algorithm that takes its cues from the foraging strategy of sparrows is called the sparrow search algorithm (SSA). While SSA is competitive when compared to other algorithms, it nevertheless has a propensity to carry out imbalanced exploitation and exploration and find the local optimum. Therefore, the modified adaptive sparrow search algorithm (MASSA), an SSA modification, is created to address these problems. To increase population variety, the MASSA uses a chaotic reverse learning technique. Second, to balance the exploitation and exploration capacities, a dynamic adaptive weight is added. In the end, an adaptive spiral search technique improves algorithm performance. Among 23 classical test functions, of which 13 are multidimensional and the other 10 are fixed dimensional, the best chaotic operator is found. It is proven that MASSA is superior. Simulation studies demonstrate that the MASSA described in this study is superior to previous algorithms in terms of stability, convergence speed, and convergence accuracy. Finally, a sample robot path planning problem is resolved using MASSA, and the experimental outcomes confirmed the viability and usefulness of MASSA. [ABSTRACT FROM AUTHOR]

For the meting process of glass-ceramics, the melts are simulated by using analytically pure materials high temperature. The effects of La2O3 on the viscosity and structure for the CaO-SiO2-MgO-Al2O3 melt are studied via both rotating-cylinder method and Raman spectroscopy. The results show that the viscosity and viscous flow activation energy decreases as the La2O3 content increases. The addition of La2O3 destroyed the silicate structural units(Qn)m the met. The percent of Q¹,Q² units increases with increasing amount of La2O3. However, the percent of Q³ units decreases with increasing amount of La2O3. In addition, the percent of Q0 units are slightly dependent on the La2O3 content. It indicates that the addition of La2O3 increase the number of non-bridging oxygen in the state structural units and reduce the degree of polymerization. La2O3 pay a role as network modifier in the melt. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The combustion activity improved significantly by adding Fe 2 O 3 and CeO 2. • Reduction of NO by CO was enhanced effectively by adding Fe 2 O 3 and CeO 2. • The combined process of catalytic combustion and catalytic denitration is proposed. • Synergistic catalytic effect of ferric oxide and cerium oxide is proposed. Abstract The processes of catalytic combustion and catalytic denitration of semi-coke were conducted in the presence of catalysts Fe 2 O 3 and CeO 2, The comprehensive performance of these processes was evaluated with thermogravimetry analysis and infrared spectroscopy. The results indicate that the combustion activity improved significantly when we added Fe 2 O 3 and CeO 2 separately. Furthermore, the mixture of Fe 2 O 3 and CeO 2 has better combustion efficienty. When Fe 2 O 3 and CeO 2 were added separately, there was a decline in NO and CO emission (NO: 10.11% vs. 6.48%, CO: 7.18% vs. 5.28%). Meanwhile, the mixture of Fe 2 O 3 and CeO 2 caused a great decline in the total amounts of NO and CO emission (NO: 20.70%, CO: 16.33%). The denitration effect is ascribed to the homogeneous reduction of NO by CO, enhanced by adding the catalysts CeO 2 and Fe 2 O 3. Fe 2 O 3 and CeO 2 are catalytically active in promoting not only coke combustion but also NO reduction. Fe 2 O 3 and CeO 2 are associated, synergically catalyzing the semi-coke combustion. [ABSTRACT FROM AUTHOR]

Graphical abstract Synergistic catalytic denitration process over the Fe 2 O 3 and CeO 2 mixture. Highlights • Iron and rare earth minerals enhanced the reduction of NO by CO. • Fe 2 O 3 and CeO 2 synergistically catalyzed the reduction of NO by CO. • CeO 2 promote the redox cycle of the Fe 2 O 3 catalyst. Abstract The catalytic activities of iron concentrate, rare earth concentrate, and rare earth tailings for semi-coke denitration were studied using thermogravimetric analysis combined with Fourier transform infrared spectroscopy. The results revealed that less NO was produced from semi-coke combustion with the addition of iron and rare earth minerals, and meanwhile CO production was reduced as well. It is likely that the addition of iron and rare earth minerals enhances the homogeneous reduction of NO by CO thus improving the removal efficiency of nitrogen oxides. The catalytic activity of rare earth tailings was higher than those of rare earth concentrate and iron concentrate. It is evidenced that ferric oxide and rare earth oxides in the tailings are associated, synergically catalyzing the homogeneous reduction of NO by CO. [ABSTRACT FROM AUTHOR]

• The study combines computational and experimental work on the Mo x Ce 1- x PO 4. • The incorporation of Mo improved the NH 3 -SCR activity on the Mo x Ce 1- x PO 4. • The reaction mechanism followed the Eley-Rideal and Langmuir-Hinshelwood mechanism. Developing CePO 4 -based NH 3 -SCR catalysts with high NO x conversion, N 2 selectivity, and SO 2 tolerance at low temperatures is challenging. Analyzing the atomic-level surface structure of these catalysts is particularly important. Hence, we conducted a combined computational and experimental study to design the surface structure of Mo x Ce 1- x PO 4 catalysts, corroborate the reaction performance and structural sensitivity, and investigate the relationship between active sites and structural performance at the atomic level. DFT calculations were used to systematically investigate the NH 3 and NO adsorption capacity of the Mo-doped CePO 4 solid solution structure model. The rationality of using the Mo-doped CePO 4 solid solution structure as a catalyst was further supported by DFT calculation data and experimental results from BET, XRD, Raman, SEM, TEM, HR-TEM, NH 3 -TPD, H 2 -TPR, XPS and in situ DRIFTS. The source of the excellent intrinsic NH 3 -SCR activity of the Mo-doped CePO 4 solid solution structure is disclosed. The role of the Mo dopant in the Mo-doped CePO 4 solid solution as an SO 2 trapping site to protect the catalytic active site from sulfation is discussed from a molecular perspective. [ABSTRACT FROM AUTHOR]

• The equilibrium potentials of forming Nd-Fe intermetallic compounds were measured. • The Nd 2 Fe 17 film was prepared by electrochemical method. • Reaction kinetics of forming Nd 2 Fe 17 intermetallic compound was studied. Nd 2 Fe 17 intermetallic compound exhibits excellent magnetic and microwave absorption properties due to its high saturation magnetization. This work investigated the electrochemical behaviors of neodymium ions on a solid iron electrode in molten LiF, focusing on the reaction kinetics of forming Nd 2 Fe 17 intermetallic compound. The results showed that Nd 2 Fe 17 firstly and then Nd 5 Fe 17 intermetallic compounds formed on the iron electrode. The equilibrium electrode potentials for forming the two intermetallic compounds were measured by open circuit chronopotentiometry. The reaction kinetics of forming Nd 2 Fe 17 intermetallic compound was investigated by cyclic voltammetry and chronopotentiometry. The electrode reaction of forming Nd 2 Fe 17 intermetallic compound was an irreversible process that was diffusion-controlled. The diffusion activation energy and heterogeneous charge transfer rate constant were obtained. The research on the reaction kinetics indicated that the charge transfer rate could be improved by increasing overpotential. The Nd 2 Fe 17 intermetallic compound was successfully prepared on a solid iron electrode by potentiostatic electrolysis. [ABSTRACT FROM AUTHOR]

• Nb is mainly in the +5 valence state and exists in the form of [NbO 6 ]7− octahedron. • The melt conductivity increases with the increase of Nb 2 O 5 content. • Ti in the melt is dominated by Ti4+ and exists in the [TiO 6 ]8− octahedron structure. Electrical conductivity is a very important physical parameter in the process of electrolytic extraction of niobium from molten niobium-enriched slag or preparation of ferroniobium alloy by reduction melting separation in electric arc furnace. The effects of Nb 2 O 5 , CaO/SiO 2 ratio and TiO 2 on the electrical conductivity of CaO-SiO 2 -Nb 2 O 5 -TiO 2 -CeO 2 -CaF 2 melt were studied by AC four-electrode method. The melt structure was studied by XPS to reveal the change rules of melt conductivity. The results show that the addition of Nb 2 O 5 or increasing the CaO/SiO 2 ratio in the melt can depolymerize the melt network structure and effectively improve the melt conductivity, and the activation energy of the conductivity is negatively correlated with the Nb 2 O 5 content and the CaO/SiO 2 ratio. With the increase of TiO 2 content in the melt, the melt network structure polymerizes, the melt conductivity decreases, and the activation energy of conductivity also showed a decreasing trend. [ABSTRACT FROM AUTHOR]

• The viscosity was proportional to the CeO 2 content and the CeO 2 /Al 2 O 3 ratio. • CeO 2 made the structure of the silicon oxide ionic group to be simple. • The viscosity of the melt was influenced by the combination of Ce4+ and Ce3+. The effect of the CeO 2 content and CeO 2 /Al 2 O 3 ratio on the melt viscosity of CaO-SiO 2 (-Al 2 O 3)-CeO 2 was determined using the rotating cylinder method. The structural characteristics of the quenched vitreous samples were investigated with a Raman spectrometer. The results showed that the melt viscosity of CaO-SiO 2 (-Al 2 O 3)-CeO 2 decreased significantly with increases in the CeO 2 content and the CeO 2 /Al 2 O 3 ratio. Q 3/ Q 2, which represents the degree of polymerization of the melt, decreased with an increase in the CeO 2 content and the CeO 2 /Al 2 O 3 ratio. Ce in the CaO-SiO 2 (-Al 2 O 3)-CeO 2 system was present as a mixture of Ce4+ and Ce3+ in high-purity Ar atmosphere at a temperature of 1540 °C. In the CaO-SiO 2 (-6%Al 2 O 3)-6%CeO 2 system, the melt viscosity was higher in the presence of Ce4+ and Ce3+ than in the presence of Ce3+, indicating that the melt viscosity of CaO-SiO 2 (-Al 2 O 3)-CeO 2 was determined by the combination of Ce4+ and Ce3+. CeO 2 acted as a network modifier in the melt. [ABSTRACT FROM AUTHOR]

The microstructure and hydrogen storage characteristics of V 48 Fe 12 Ti 15- x Cr 25 Al x (x = 0, 1) alloys prepared by vacuum arc melting were studied by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and pressure–composition isotherm measurements. It was confirmed that all of the alloys comprise a BCC phase, a Ti-rich phase, and a TiFe phase. Al as a substitute for part of the Ti content caused an increase of lattice parameters of the BCC phase and of the equilibrium pressures of hydrogen desorption, but decrease of the hydrogen storage capacities. The kinetic mechanism of the hydrogenation and dehydrogenation of the alloys was investigated by the classical Johnson–Mehl–Avrami equation. The reaction enthalpies (Δ H) for the dehydrogenation of alloys without and with Al were calculated by the Van't Hoff equation based on the PCI measurement data, which are 30.12 ± 0.14 kJ/mol and 28.02 ± 0.46 kJ/mol, respectively. The thermal stability of the metal hydride was measured by differential scanning calorimetry. The hydrogen desorption activation energies were calculated using the Kissinger method as 79.41 kJ/mol and 83.56 kJ/mol for x = 0 and 1, respectively. The results suggest that the substitution of titanium with aluminum improves the thermodynamic properties of hydrogen storage and reduces the kinetic performance of hydrogen desorption. • The V 48 Fe 12 Ti 15- x Cr 25 Al x (x =0, 1) alloys were prepared by vacuum arc melting. • The alloys consist of BCC phase, Ti-rich phase and TiFe phase. • The alloys have higher hydrogen desorption rate of about 88%. • The substitution of Ti with Al improves the thermodynamic properties. • The substitution of Ti with Al reduces the kinetic performance of dehydrogenation. [ABSTRACT FROM AUTHOR]

Abstract Mg 80– x Ni 20 Y x (x = 0–7) alloys were successfully prepared by using the vacuum induction melting method. The structural characterizations of the alloys were performed by using X-ray diffraction, scanning electron microscope, transmission electron microscope and X-ray photoelectron spectroscopy measurements. The effects of yttrium content on the microstructure and hydrogen storage properties of the as-cast alloys were investigated. The alloys are composed of a primary phase of Mg 2 Ni, lamella eutectic composites of Mg + Mg 2 Ni, and some amount of YNi 3. The YNi 3 has completely transformed into in situ formed nanoscale YH 2 and YH 3 , with the formation of Mg 2 NiH 4. Pulverization of the alloy particles was observed during the hydrogen absorption and desorption cycles. However, the phase composition remains unchanged even after 20 hydrogenation cycles. Yttrium addition significantly improved the hydrogen-absorption kinetic performance of the alloy. In addition, pressure-composition-temperature measurements indicated that the entropy and enthalpy changes for the formation and decomposition of MgH 2 and Mg 2 NiH 4 gradually decreased with the increase of yttrium content. Highlights • YNi 3 , Mg 2 Ni and lamella eutectic Mg + Mg 2 Ni phases were observed in the alloys. • YNi 3 fully decomposed, with the formation of nanometer YH 2 and Mg 2 NiH 4. • Increasing Y content significantly improves the hydrogen absorption kinetics. • The decomposition peak temperature was reduced from 586 K to 523 K. • Δ H and Δ S of the Mg/MgH 2 and Mg 2 Ni/Mg 2 NiH 4 transformations decreased. [ABSTRACT FROM AUTHOR]

Highlights • The Mg 85 Ni 15 -0.2 wt.% Ti and Mg 68 Ti 9 Ni 23 alloys were produced by casting. • The Mg 85 Ni 15 -0.2 wt.% Ti alloy had hydrogen storage capacity of 5.22 wt.% at 653 K. • Intersection of initial hydriding curves for different temperatures were discussed. • The dehydrogenation activation energies of the two alloys were much lower than MgH 2. • The hydrogenation enthalpy of Mg 85 Ni 15 -0.2 wt.% Ti was 5KJ/mol lower than MgH 2. Abstract The as-cast Mg 85 Ni 15 -0.2 wt.% Ti and Mg 68 Ti 9 Ni 23 alloys were produced with vacuum induction levitation melting furnace. The Mg 85 Ni 15 -0.2 wt.% Ti alloy had a reversible hydrogen storage capacity of 5.22 wt.% at 653 K. Intersection of hydrogen absorption curves at different temperatures, which could be found during the initial hydrogenation process, indicated two competed kinetic mechanism took part in the original hydrogenation. Pressure-composition isothermal (PCI) curves showed two pressure plateaus for all applied temperatures. The enthalpies, obtained by PCI data, of hydrogenation for these two alloys were estimated to be about 5 kJ/mol lower than MgH 2. Results of Kissinger plots, based on DSC data, showed the activation energy of dehydrogenation were 51.69 kJ/mol and 57.75 kJ/mol, which were much lower than pure MgH 2 , for Mg 85 Ni 15 -0.2 wt.% Ti and Mg 68 Ti 9 Ni 23 alloys, respectively. [ABSTRACT FROM AUTHOR]

We proposed a simple and high value-added technology for recycling NdFeB waste. Neodymium was successfully separated from FeNd alloy by chemical dealloying reaction FeNd + 2NdCl 3 → 3NdCl 2 + Fe in molten chlorides. In the dealloying process, the porous iron alloy with small pores (around 10 nm) and high surface area (2 ∼ 20 × 104 cm2 cm−3) was prepared. The separated neodymium can be recycled as metallic neodymium by spontaneous disproportionation 3NdCl 2 (l) → 2NdCl 3 (l) + Nd(s). In other words, the FeNd alloy only needs to be dipped in molten chloride to obtain metallic neodymium and porous iron alloy by the chemical dealloying method. And the LiCl-NdCl 3 salts can be recyclable. [Display omitted] • The chemical dealloying method of recycling NdFeB wastes was proposed. • The reaction process of the chemical dealloying method was revealed. • Nd was separated from FeNd alloy while porous iron alloy was prepared. Neodymium-iron-boron (NdFeB) magnets are the rare earth products with the largest output, and their recycling is of significance for the sustainable development of rare earth resources. Currently, the recycling technology of NdFeB wastes is more concerned with the recovery of rare-earth elements, while iron is regarded as a low-value by-product. In this work, chemical dealloying method in molten chlorides was proposed to separate neodymium from FeNd alloy and simultaneously to prepare porous iron alloy. The effects of the molar ratio of reactants, dealloying temperature and time on the separation efficiency of neodymium were investigated. The maximum separation efficiency of neodymium from FeNd alloy can reach 96 %. The separation process of neodymium and the formation process of porous iron alloy were estimated based on the ICP, XRD, XPS, SEM-EDS analyses of recycled products. Neodymium was separated from FeNd alloy by the reaction with Nd(III) ions to form Nd(II) ions in molten chlorides, while the porous iron alloy was formed. The formed Nd(II) ions can be transformed into Nd(III) ions and metallic neodymium particles by the disproportionation reaction. In the process, Nd(III) ions can act as a complement to react with FeNd alloy. And neodymium was recovered in the form of metallic neodymium and NdOCl from the chloride melt and the rinsing solution of porous iron alloy, respectively. The formed porous iron alloy had the surface area of unit volume in the range of (2 ∼ 20) × 104 cm2 cm−3, the pore width around 10 nm and good hardness. The porous iron alloy is a high value-added product. [ABSTRACT FROM AUTHOR]

• The M-doped CePO4 catalysts were prepared by the coprecipitation method. • The incorporation of M improved the NH 3 -SCR activity on the CePO 4. • The reaction mechanism followed the Eley-Rideal and Langmuir-Hinshelwood mechanism. A series of Metals doped M-CePO 4 (M =Zr, Co, Mo, Cu) catalysts were prepared via the coprecipitation method for selective catalytic reduction of NO with NH 3 (NH 3 -SCR). The results showed that the NO x conversion of M-CePO 4 were higher than that of CePO 4 , especially the Mo-CePO 4 catalysts exhibited the best low-temperature activity and N 2 selectivity, the Mo-CePO 4 catalysts can reach about 99% at 300 °C and excellent 70 h long stability with the coexistence of SO 2 and H 2 O. The effect of metal elements doping on physiochemical properties of catalysts were characterized by XRD, BET, Raman, TEM, XPS, H 2 -TPR and NH 3 -TPD. SEM and TEM analysis. The results showed that part of M ions doped into CePO4 lattice resulted in lattice shrinkage. More importantly, the MO x species could not only increased the relative content of Ce3+ and surface adsorption oxygen (O′) of M-CePO 4 catalysts, but also increased the specific surface area of the catalysts. It could provide more reaction sites for active gas to promote the activation of NH 3 and enhance oxidation–reduction performance. The in-situ DRIFTS results suggested that NH 3 were adsorbed on both Lewis and Bronsted acid sites which can easily react with NO x gas. The NO species were adsorbed on Mo-CePO 4 in the form of bidentate nitrate. The main reactants of Mo-CePO 4 catalysts were NH 3 linked to Lewis acid sites and bidentate nitrate species on the catalytic surface. The Eley–Rideal and Langmuir–Hinshelwood mechanisms coexisted in the SCR reaction route. According to the characterization results of the catalysts, the mechanism of Mo promoting the activity of NH 3 -SCR at low temperature was proposed (Fig. 13.). NH 3 binds to Lewis acid centers, and NH4+ adsorbs on Brønsted acid centers, monotone nitrates and bidentate nitrates. Studies had shown that NH 2 is an important medium in the reaction of NO (gas phase) to produce NH 2 NO and then decompose into N 2 and H 2 O. As shown in Fig. 12(a), the reaction of NH 3 -SCR on the catalyst follows the Eley-Rideal (E-R) mechanism. The NH 3 Lewis acid sites and NH4+ acid sites adsorbed on Brønsted react with NO (gas phase). As shown in Fig. 12(b), monodentate and bidentate nitrates reacted with adsorbed NH 3 species, following the Langmuir-Hinshelwood (L-H) mechanism [51]. The Mo6+/Mo5+ and Ce4+/Ce3+ redox cycles on the catalyst surface participate in the whole process of the catalytic reaction. At this stage, the electron transfer process promoted the conversion of oxygen vacancy and unsaturated chemical bond, thus enhancing the adsorption activation capacity of NO and NH 3 , promoting the decomposition of NO molecule, and improving the catalytic performance. The –NH 2 s species were intermediate adsorbed and reacted with the activated nitrate, eventually becoming N 2. In the process of NO reduction, NH 3 showed selectivity to the reaction intermediates, preferentially reacted with monotone nitrate and bidentate nitrate. [Display omitted] [ABSTRACT FROM AUTHOR]

In this study, glass-ceramics were prepared from stainless steel slag and iron tailing. Consequently, unstable heavy metals were converted to stable. With the adding of stainless steel slag, crystallization temperature and the mechanical properties of the resultant glass-ceramics increased first and then decreased, and it was found that secondary phase (Spinel) differed from major phase (Augite). The results of toxicities leaching test and Tessier five step sequential extraction showed that Cr content in the exchangeable state, carbonate bind state, ferromanganese oxide state and organically bind state of the basic glass were 0.04%, 0.08%, 7.82% and 1.13%, respectively. However, in the glass-ceramics, they exhibited the low content of 0, 0.04%, 2.02% and 0.40%. The residual content of Cr reached to 90.93% in the glass, whereas 97.55% in the glass-ceramics, being higher than that in the glass. The results indicated that Cr enters the silicate lattice, so as to realize the curing of chromium. • Preparation of glass-ceramics by iron tailings and stainless steel slag. • The residual state (stable state) of chromium in glass-ceramics was 98.9%. • TCLP results demonstrate the superiority of glass-ceramics in solidification Cr. • Glass-ceramics samples have excellent physical properties. [ABSTRACT FROM AUTHOR]

REEs are selectively separated from REPM wastes. The separated REEs are recycled in the form of rare-earth metals which can be directly applied in industry. Forming anode channels make the separation of REEs in the inside of REPM wastes feasible. • Rare-earth metal was directly recycled from REPM waste. • Forming anodic channels facilitated the oxidation of rare-earth elements inside the REPM waste. • The formation parameter and process of channels were proposed. Tens of thousands of tons of rare-earth permanent magnet (REPM) wastes are produced worldwide every year. The recovery of rare-earth elements from the wastes can effectively reduce the exploitation of rare-earth minerals. The recovery of neodymium and praseodymium from a REPM waste is investigated by electrolysis in molten LiF-CaF 2 where no anode gas releases, making the process environmentally attractive. Neodymium and praseodymium are selectively oxidized from the REPM waste and transformed into rare-earth ions. To facilitate the oxidation of rare-earth elements inside the REPM waste, we intended to make REPM electrode form channels by oxidation of Nd-Pr and Nd 2 Fe 14 B alloys. By analyzing the microstructure of REPM electrode after forming channels, it can be found that the channels provide continuous transport access of the electrolyte to the inside of the REPM electrode. The separation rates of Nd and Pr increase with increasing current, while the rate of oxidation reaction is proportional to current. In addition, the oxidation of Fe initially occurs at the inside of the REPM electrode where rare-earth elements have been first depleted. The separated rare-earth ions are directly prepared as rare-earth metals at the cathode by electrolysis, leaving the porous Fe 2 B alloy and metallic Fe. [ABSTRACT FROM AUTHOR]

The surface properties of the modified rare earth concentrate supported by γ-Al 2 O 3 and the factors affecting the catalytic activity were studied. Roasting and NaHCO 3 -oxalic acid leaching were used to study on surface properties of modified rare earth concentrates. The effects of modification treatment on the microstructure and catalytic activity of the impurity-removed samples were characterized by XRD, BET, TPD, TPR, XPS, in-situ DRIFTS. The results show that the optimum nitrogen removal efficiency of the modified rare earth concentrate loaded γ-Al 2 O 3 sample can reach 80.5%. For rare earth concentrates, the oxalic acid and the mineral are co-calcined together, and then leached by a NaHCO 3 , the content of calcium fluorophosphate and calcium fluoride is remarkably small, and the content of Ce 7 O 12 in the active powder is increased and the dispersion is more uniform. Active ingredients on the sample surface such as Ce, La, Mn were increased, the specific surface area of the sample was increased. The redox capacity of the rare earth concentrate surface and the NH 3 adsorption performance are enhanced. Ce coexists in the form of Ce3+ and Ce4+. Mn coexists in the form of Mn3+ and Mn4+. The synergistic action of cerium and manganese increases catalytic activity. • The catalyst is prepared by the method of calcination-NaHCO 3 -oxalic acid. • The maximum denitration rate of the catalyst can reach 80.5%. • The content of the active substance Ce 7 O 12 in the active powder is increased. • The redox capacity and NH 3 adsorption performance of the catalyst surface are improved. • The synergistic effect of cerium and manganese increases the catalytic activity. [ABSTRACT FROM AUTHOR]

We proposed a simple and sustainable approach to recover rare earths and iron from an ultrafine NdFeB waste. Rare earths were directly recovered by one-step precipitation in hydrofluoric acid and the dissolved iron was recovered in the form of nano-scale FeF 2 (s) and Fe(s) by electrodeposition. The hydrofluoric acid, which has removed iron by electrodeposition, could be still used for the leaching of the waste, making the hydrofluoric acid recyclable. • A simple and sustainable approach was proposed to recover rare earths and iron from an ultrafine NdFeB waste. • Rare earths were directly recovered by one-step precipitation. • The chemicals used in this approach were recyclable. In this work, a simple and sustainable approach is proposed to recover rare earths and iron from an ultrafine NdFeB waste. Rare earths are directly recovered by one-step precipitation in hydrofluoric acid and the dissolved iron by electrodeposition. The rate constant and activation energy of the reaction of rare earth hydroxide with hydrofluoric acid are investigated to understand the kinetics of iron leaching and rare earth precipitation. The rare earth precipitation is much faster than the iron leaching, enabling the rare earths separation from iron after a complete iron dissolution. The cathodic deposits of iron were characterized by X-ray photoelectron spectrometer (XPS) and scanning electron microscope (SEM). The nano-scale FeF 2 (s) and Fe(s) were deposited on Pt electrode in hydrofluoric acid solution with pH 2.3 and pH 2.89, respectively. The reduction of Fe(III) to Fe(0) was investigated by cyclic voltammetry, chronopotentiometry and open circuit chronopotentiometry. This reduction was a quasi-reversible process which was controlled by diffusion. The temperature dependence of the diffusion coefficient was established as lnD = −9.84 − 1805.43/ T and the activation energy value of the diffusion process was calculated to be −15.01 kJ mol−1. The relationship between the Gibbs energy of intermetallic Fe-Pt formation and the temperature was established to be Δ G = −487.53 + 0.936 T. The hydrofluoric acid after the electrodeposition could be recycled for the leaching of the ultrafine NdFeB waste again. [ABSTRACT FROM AUTHOR]

Impurity removal and modification of rare earth concentrate powder were conducted by roasting weak acid-weak alkali leaching to obtain the active components of denitrification catalysts. NH3 selective catalytic reduction catalyst samples were prepared by mixing and kneading with pseudo-γ-Al2O3 boehmite as carrier. The results showed that the Ce7O12 content in the active component samples increased and dispersed more evenly. The grain size of the samples was refined, the specific surface area increased, and the active sites exposed more. Ce coexists in the form of Ce3+ and Ce4+. Fe coexists in the form of Fe3+ and Fe2+, but Fe3+ is abundant. Some Ce, La, Nd, Pr, Fe, Mn, and other components formed solid melts during preparation, which increased the synergistic catalytic effect. The denitrification efficiency of the catalyst sample was 92.8% under the conditions of reaction temperature 400 °C, NO content was 600 ppm, NH3/NO ratio was 1.5, and O2 concentration was 4%. [ABSTRACT FROM AUTHOR]

It is a useful way to stabilize the elements of heavy metal in the glass-ceramics with the form of ions due to the environmental pollution of heavy metal, such as Cr. The glass-ceramics of excellent combination properties were prepared, and the effect of stabilizing Cr-containing stainless steel slag with different concentrations of nitric acid leaching test were investigated. It was found that the major crystalline phase was diopside or anorthite with or without the amount stainless steel slag. Moreover, the continuous refinement of grains exhibited with the increase of amount of stainless steel slag. The results indicated that the excellent physical and mechanical properties, including density (2.9 g/cm3), hardness (729.27HV0.3), bending strength (222.9 MPa), and the solid solution of Cr in excess of 0.00057% for the glass-ceramics were related to the change of microstructure and phase structure. There showed the potential for reusing and detoxifying stainless steel slag. [ABSTRACT FROM AUTHOR]