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Taking a tailings in Inner Mongolia as the research object, the process mineralogy was studied. The results of multi-element analysis showed that the REO content in the raw materials was 6. 2%, and the results of mineral composition analysis showed that the rare earth minerals were mainly cerium fluorocarbon and monazite, and also contained a small amount of cerium fluorocarbonite and Yellow River minerals. The gangue minerals were mainly iron minerals, fluorite, pyroxene, amphibole, and so on. The results of particle size sieve analysis showed that the particle size was 62.9% passing 25 µm, and the fine particle size of rare earth minerals would adversely affect the flotation recovery. The adsorption kinetics were studied, and the effects of P8 dosage and pH value on the floatability of the minerals were investigated by the adsorption kinetics study, and the optimal pH value of the fluorocerite flotation was 9. The kinetic fitting of P8 adsorption by the kinetic equation shows that P8 has strong capture ability, and the appropriate dosage can completely float the basilite. In the flotation tests, the hydroxamic acid collector P8 has good capture performance and selectivity, and the sodium silicate having good inhibitory effect on gangue minerals pyroxene and amphibole minerals were used as inhibitors. FM-132 was used as foaming agent. Laboratony experiments were carried out to determine the optimal flotation conditions such as collector dosage, inhibitor dosage, slurry concentration, flotation temperature and flotation time. Through a locked-cycle process of one roughing and two cleanings, a rare earth concentrate with a grade (REO) of 51.85% and a recovery of 79.12% can be obtained, which can effectively separate and recover the rare earth minerals in the tailings, and provide technical support for the recovery and application of rare earth in the industry, so as to realize the efficient utilization of rare earth resources. [ABSTRACT FROM AUTHOR]

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]

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]

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]

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]

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]

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]