离子型稀土矿山淋洗及尾水富集试验研究

对浸矿后离子型稀土原地浸矿场采用清水进行淋洗，在184天的清水淋洗过程中，尾水氨氮值从最开始的507mg/L，降低至140mg/L，淋洗尾水pH4.52~3.10。淋洗尾水采用两级反渗透膜分离，既回收有价资源稀土，又能使出水氨氮达标。结果表明，产水氨氮浓度稳定低于15mg/L，对稀土的截留率高于98.25%，浓水中稀土离子平均浓度313.4mg/L，可进一步回收稀土资源。     

Effect of scandium and zirconium alloying on microstructure and gaseous hydrogen storage properties of YFe3

RM₃ compounds (R = rare earth metals, M = transition metals) have rarely been studied for gaseous hydrogen storage applications because of unfavorable thermodynamics. In this work, the hydrogen storage properties of a single-phase YFe₃ alloy were improved by non-stoichiometric composition and alloying with Sc and Zr. Only the Y_1.1–ySc_yFe₃ (y = 0.22, 0.33) alloys consist of a single rhombohedral phase. The Sc substitution for Y leads to the reduction in the unit cell volume of the YFe₃ phase, and thus significantly increases the dehydriding equilibrium pressure and decreases the dehydrogenation temperature. The alloy Y_0.77Sc_0.33Fe₃ delivers a decomposition enthalpy change of 33.54 kJ/mol and a lowest dehydrogenation temperature of 135 °C, in comparison with 38.99 kJ/mol and 165 °C for the alloy Y_1.1Fe₃. The Zr substitution causes a similar thermodynamic destabilization effect, but the composition and microstructure of Y–Zr–Fe alloys need to be further optimized.     

Effect of Pr-Ga dual-alloys diffusion on magnetic properties and thermal stability of hot-deformed PrNd-Fe-B magnets

To investigate the influence of the addition of Pr–Ga alloys on magnetic properties and morphology of materials, the hot-deformed PrNd-Fe-B magnets were prepared by the addition of Pr–Ga alloys using a dual-alloys diffusion. The room-temperature coercivity of the hot-deformed PrNd-Fe-B magnets increases substantially from 1.68 to 2.34 T, while the remanence decreases from 1.42 to 1.24 T, by the addition of 5 wt% Pr–Ga alloys. Moreover, the thermal stability of coercivity improves from ?0.46%/^oC to ?0.42%/^oC. Two types of grain boundary phases (PrNd-rich and PrNd-Ga-rich) are generated at grain boundaries by microstructural analysis, resulting in the decrease of Fe element concentration from more than 60% to about 10% at grain boundaries. The decrease of ferromagnetic element concentration at grain boundaries and the refinement of grain are considered to be the main reasons for the improvement of coercivity and thermal stability.     

Behavior of phase transformation of Baotou mixed rare earth concentrate during oxidation roasting

Based on the new process named “Combination Method” for metallurgy and separation of Baotou mixed rare earth concentrate (BMREC), the aim of this paper is to clearly elucidate the phase change behavior of BMREC without additives during oxidative roasting at 450–800 °C. The results indicate that the bastnaesite in BMREC is decomposed at 450–550 °C, the weight loss is about 10.3 wt%, and the activation energy (E) is 144 kJ/mol. The bastnaesite in BMREC is decomposed into rare earth fluoride, rare earth oxides (La₂O₃, Ce₇O₁₂, Pr₆O₁₁ and Nd₂O₃), and CO₂, particularly, with the increase of roasting temperature, bastnaesite in BMREC is more completely decomposed into LaF₃, which causes a decrease in leaching rate of La during the HCl leaching process. Additionally, the maximum cerium oxidation efficiency reaches about 60 wt% when the roasting temperature is equal to or above 500 °C, and the oxidation reaction rate of cerium increases with the increasing roasting temperature.     

Revealing active species of CePO4 catalyst for selective catalytic reduction of NOx with NH3

Revealing the active species of the catalyst is conducive to the design of more efficient catalyst. Herein, we tried to demonstrate the roles of amorphous and crystalline structures on CePO₄ catalyst during selective catalytic reduction (SCR) of NO_x by NH₃. Higher calcination temperature promotes the transfer of amorphous structure to crystalline structure on the surface of CePO₄. Both amorphous and crystalline CePO₄ species on CePO-X samples can provide acid sites for NH₃ adsorption, but the former can provide more acid sites. The superior redox property of surface amorphous CePO₄ species contributes to its high NH₃-SCR activity at low temperature, but it also leads to the decrease of high temperature (>350 °C) NH₃-SCR activity due to the oxidation of NH₃. In contrast, crystalline CePO₄ species shows high activity only at high temperature because of its poor redox property. Therefore, it can be inferred that amorphous and crystalline structures on CePO₄ catalyst can be the efficient active species of NH₃-SCR at low and high temperature, respectively.     

In-situ measurement of mineral phase transition and kinetics in roasting process of Bayan Obo mixed rare earth concentrate by sodium carbonate

In this study, the Bayan Obo rare earth concentrates mixed with Na₂CO₃ were used for roasting research. The phase change process of each firing stage was analyzed. The kinetic mechanism model of the continuous heating process was calculated. This study aims to recover valuable elements and optimize the production process to provide a certain theoretical basis. Using X-ray diffraction (XRD), Fourier infrared spectroscopy, scanning electron microscopy with energy dispersive spectrometry, the reaction process and the existence of mineral phases were analyzed. The variable temperature XRD and thermogravimetric method were used to calculate the roasting kinetics. The phase transition results show that carbonate-like substances first decompose into fine mineral particles, and CaO, MgO, and SiO₂ react to form silicates, causing hardening. Further, REPO₄ and NaF can directly generate CeF₃ and CeF₄ at high temperatures, and a part of CeF₄ and NaF forms a solid solution substance Na₃CeF₇. Rare earth oxides calcined at a high temperature of 750 °C were separated to produce Ce_0.6Nd_0.4O_1.8, Ce₄O₇, and LaPrO_3+x. Then, BaSO₄, Na₂CO₃, and Fe₂O₃ react to form barium ferrite BaFe₁₂O₁₉; the kinetic calculation results show that during the continuous heating process, the apparent activation energy E reaches the minimum in the entire reaction stage in the temperature range of 440–524 °C, and the reaction order n reaches the maximum, which indicates that the decomposition product REFO significantly impacts the reaction system and reduces the activation energy. The mechanism function is F(α) = [?ln (1?α)]^1/3. The reaction order n reaches the minimum in the temperature range of 680–757 °C, and the apparent activation energy E is large. The difficulty of the reaction increases during the final stage. The reaction mechanism function is F(α) = [1?(1?α)^1/3]². Observing the entire reaction stage, the step of controlling the reaction rate changes from random nucleation to three-dimensional diffusion (spherical symmetry).     

Unraveling specific role of carbon matrix over Pd/quasi-Ce-MOF facilitating toluene enhanced degradation

Metal organic frameworks (MOFs) derivatives represented by quasi-MOFs have excellent physical and chemical properties and can be applied for the catalytic combustion of volatile organic compounds (VOCs). In this work, Pd/quasi-Ce-BTC synthesized by simple one-step N₂ pyrolysis was applied to the oxidation of toluene, showing excellent toluene catalytic activity (T₉₀ = 175 °C, 30000 mL/(g·h)). Microscopic analyses indicate the formation and interaction of a carbon matrix composite quasi-MOF structure interface. The results show that the amorphous carbon matrix formed during the partial pyrolysis of Ce-BTC significantly improves the adsorption and activation capacity of toluene in the reaction, and constructs a reductive system to maintain high concentrations of Ce³⁺ and Pd⁰, which can facilitate the activation and utilization of oxygen in reaction. Quasi in-situ XPS proves that carbon matrix is indirectly involved in the activation and storage of oxygen, and Pd⁰ is the crucial active site for the activation of oxygen. Stability and water resistance tests display good stability of Pd/quasi-Ce-BTC. This work provides a potential method for designing quasi-MOF catalysts towards VOCs effective abatement.     

Site occupation and energy transfer in full color emitting phosphor Ba2Ca(BO3)2:Ce3+(K+),Eu2+,Mn2+

White light-emitting diodes (WLEDs) fabricated by single-phase full color emitting phosphor are an emerging solution for health lighting. The crystallographic site occupation of activators in a proper host lattice is crucial for sophisticated design of such phosphor. Here, we report a high quality white light-emitting phosphor Ba₂Ca(BO₃)₂:Ce³⁺(K⁺),Eu²⁺,Mn²⁺ with spectral distribution covering whole visible region. Blue light emission originates from Ce³⁺ ions occupying preferentially Ba²⁺ site by controlling synthesis conditions. Green and red lights are obtained from Eu²⁺ occupying Ba²⁺ (and Ca²⁺) site and Mn²⁺ occupying Ca²⁺ site, respectively. In this triple-doped phosphor, strong red emission with a low concentration of Mn²⁺ is realized by the efficient energy transfer from Ce³⁺ and Eu²⁺ to Mn²⁺. Furthermore, high quality white light is accomplished by properly tuning the relative doping amount of Ce³⁺(K⁺)/Eu²⁺/Mn²⁺ based on efficient simultaneous energy transfer. The results indicate that Ba₂Ca(BO₃)₂:Ce³⁺(K⁺),Eu²⁺,Mn²⁺ is a promising white light-emitting phosphor in WLEDs application.     

A comparative study of NdY-Fe-B magnet and NdCe-Fe-B magnet

Low cost and high abundance rare earth elements Y and Ce have attracted tremendous interests of the industrial and scientific societies for fabricating the highly cost-performance efficient rare earth permanent magnets. However, the effect of separate replacement of Nd by Y or Ce on the performances of NdFeB-type magnet under the same atomic ratio and preparation conditions is still unclear. In this work, we systematically investigated the magnetic properties, thermal stabilities and service performances of (Nd_0.8Y_0.2)_13.80Fe_balAl_0.24Cu_0.1B_6.04 (atomic fraction, denoted as 20Y) and (Nd_0.8Ce_0.2)_13.80Fe_balAl_0.24Cu_0.1B_6.04 (atomic fraction, denoted as 20Ce) magnets. The results demonstrate that the μ₀M_r, μ₀H_c and (BH)_max of 20Y magnet are respectively 1.325 T, 1.173 T and 343.467 kJ/m³, which are comprehensively higher than those of 20Ce magnet (μ₀M_r = 1.310 T, μ₀H_c = 0.948 T, (BH)_max = 321.105 kJ/m³). Moreover, the 20Y magnet has higher thermal stability compared with 20Ce magnet which is favorable for the magnetic performances at elevated temperatures. The investigation of microstructure and elemental distribution indicates that the excellent magnetic performances of NdY-Fe-B magnet can be attributed not only to the preferable intrinsic properties 4πM_s, H_a and T_c of Y₂Fe₁₄B, but also to the in-situ core–shell structure of the 2:14:1 matrix phase grain with Y-rich core and Nd-rich shell, along with the thicker grain boundary layer between the adjacent matrix phase grains in NdY-Fe-B magnet. Furthermore, the 20Y magnet exhibits better mechanical property and higher corrosion resistance than 20Ce magnet, which are helpful for prolonging the service life of the magnet in practical application.     

Understanding enhancing mechanism of Pr6O11 and Pr(OH)3 in methanol electrooxidation

The presence of oxygen vacancies and hydroxyl groups are both favorable for the methanol electrooxidation on Pt-based catalysts.Understanding and differentiating the enhancing mechanism between oxygen vacancies and hydroxyl groups for high activity of Pt catalysts in methanol oxidation reaction(MOR)is essential but still challenging.Herein,we developed two kinds of co-catalyst for Pt/CNTs,Pr₆O₁₁is rich in oxygen vacancies but contains substantially no hydroxyl groups,while Pr(OH)₃ possesses abundant hydroxyl groups without oxygen vacancies.After a seque nce of designed experiments,it can be found that both oxygen vacancies and hydroxyl groups can improve the performance of Pt/CNTs electrocatalysts,but the enhancing mechanism and improving degree of oxygen vacancies and hydroxyl groups for the MOR are different.Since the oxygen vacancies are more conducive to increasing the intrinsic activity of the Pt catalyst,and the hydroxyl groups play a decisive role in dehydrogenation and deproto nation of methanol,the co-catalysts with both oxygen vacancies and hydroxyl groups mixed with Pt/CNTs have higher catalytic performance.Therefore,hydroxyl-rich Pr₆O₁₁·xH₂O was prepared and used as MOR electrocatalyst after mixed with Pt/CNTs.Benefiting from the synergistic effect of oxygen vacancies and hydroxyl groups,the Pr₆O₁₁·xH₂O/Pt/CNTs shows a high peak current density of 741 mA/mg,which is three times higher than that of Pt/CNTs.These new discoveries serve as a promising strategy for the rational design of MOR catalysts with low cost and high activity.