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Silicon has been applied in many fields, such as high-purity semiconductors, high-temperature resistant materials, optical fiber connection materials, organosilicon compounds, and alloys. In this work, silicon was extracted from the Bayan Obo tailing by high-temperature electrolysis. The reduction process of Si(IV) and the effect of CaF2 content on the reduction process were studied in the SiO2–CaO–CaF2 melt. The Si(IV) ions in the SiO2–CaO system with 10 wt pct CaF2 were reduced by a one-step four-electrons transfer process. In the SiO2–CaO melt with 15, 20, and 30 wt pct CaF2, the reduction process of Si(IV) was a two-step two-electrons transfer process: Si(IV) + 2e → Si(II) and Si(II) + 2e → Si(0). The reduction process of Si(IV) to Si(II) was reversible and was controlled by diffusion. The diffusion coefficient was 1.52 × 10−8 cm2 s−1. Si and WSi2 were prepared under a current density of − 0.55 A cm−2 at 1738 K. It was found that the WSi2 alloys were formed because of the alloying of Si(IV) and W. [ABSTRACT FROM AUTHOR]

Bayan Obo tailings are rich in rare earth elements (REEs), iron, and other catalytic active substances. In this study, mine tailings were calcined at different temperatures and tested for the catalytic combustion of low-concentration methane. Upon calcination at 600°C, high catalytic activity was revealed, with 50% CH4 conversion at 587°C (space velocity of 12,000 mL/g h). The physicochemical properties of catalysts were characterized using thermogravimetric analysis, X-ray diffraction, scanning electron microscopy, hydrogen temperature-programmed reduction (H2-TPR), and X-ray photoelectron spectroscopy (XPS). Compared to the raw ore sample, the diffraction peak intensity of Fe2O3 increased post calcination, whereas that of CeCO3F decreased. A porous structure appeared after the catalyst was calcined at 600°C. Additionally, Fe, Ce, Ti, and other metal elements were more highly dispersed on the catalyst surface. H2-TPR results revealed a broadening of the reduction temperature range for the catalyst calcined at 600°C and an increase in the reduction peak. XPS analysis indicated the presence of Ce in the form of Ce3+ and Ce4+ oxidation states and the coexistence of Fe in the form of Fe2+ and Fe3+. Moreover, XPS revealed a higher surface Oads/Olatt ratio. This study provides evidence for the green reuse of Bayan Obo mine tailings in secondary resources.

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]

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]