Journal of Rare Earths最新文献

To solve the problems of the long development period, low mass transfer efficiency and high impurity content in the in-situ leaching process of weathered crust elution-deposited rare earth ores (WCE-DREO), cationic hydroxyethyl cellulose (PQ-10) was composited with conventional leaching agent ammonium sulfate ((NH₄)₂SO₄) to form a novel composite leaching agent. The effects of PQ-10 concentration, leaching temperature and leaching flow rate of the composite leaching agent on the leaching kinetics and mass transfer processes of rare earth (RE) and aluminum (Al) were investigated. Compared to the single leaching agent (NH₄)₂SO₄, the composite leaching agent (2 wt% (NH₄)₂SO₄+0.02 wt% PQ-10) can reduce the RE leaching equilibrium time from 465 to 130 min and increase the RE leaching efficiency and decrease the Al leaching efficiency. It also facilitates the leaching process of WCE-DREO by increasing the peak concentrations of RE and Al, reducing the theoretical tower plate height (HETP) and improving the leaching mass transfer efficiency. It is indicated that PQ-10 can promote the leaching of WCE-DREO. The leaching process of the composite leaching system conforms to the diffusion kinetic control model. When the PQ-10 concentration is in the range of 0.005 wt%–0.020 wt%, the reaction orders of RE and Al are 0.73 and 0.54, respectively, which shows a positive effect on the leaching velocity; when the PQ-10 concentration is in the range of 0.030 wt%–0.060 wt%, the reaction orders of RE and Al are –1.16 and –0.75, respectively, which show a negative effect on the leaching velocity. In the range of 10–50 °C, the apparent activation energies of RE and Al are 15.02 and 17.31 kJ/mol, respectively, and the higher the leaching temperature, the smaller the HETP and the higher the leaching velocity and mass transfer efficiency. The increase in leaching flow rate contributes to the increase in the longitudinal diffusion velocity of the leaching agent within WCE-DREO, causing a shorter time for RE and Al to reach leaching equilibrium. In addition, the flow rate and HETP are consistent with the Van Deemter equation. At a flow rate of 0.8 mL/min, HETP was minimized and the optimal mass transfer efficiencies is achieved for RE and Al.

The nanocrystalline samples Nd_1–xM_xFeO₃ (x = 0.0 and 0.1; M: Co²⁺ and Ni²⁺) were prepared using the citrate combustion method. The X-ray diffraction (XRD) pattern confirmed that the nanoparticles were synthesized in an orthorhombic structure. The particle size of Nd_1–xM_xFeO₃ is in the range of 29–59 nm. The selected area electron diffraction (SAED) indicates the samples were prepared in a polycrystalline nature. The samples Nd_1–xM_xFeO₃ (x = 0.0 and 0.1; M: Co²⁺ and Ni²⁺) have antiferromagnetic behavior. The Fe³⁺ spins are aligned antiparallel, forming the antiferromagnetic (AFM) properties, which are affected by many factors such as the bond angle between the Fe³⁺ (Fe³⁺–O^2––Fe³⁺) and the Dzyaloshinskii-Moriya (D-M) interaction. The doping of Co²⁺ and Ni²⁺ ions in NdFeO₃ enhances the magnetic properties of the NdFeO₃. The saturation magnetization (M_s) of Nd_0.90Co_0.10FeO₃ increases 1.8 times more than that of NdFeO₃. The exchange bias field (H_EX) of the Co-doped sample is two times greater than that of NdFeO₃. The magnetic anisotropy constant (K) of the 10 % Co-doped sample increases by 11 factors compared to that of NdFeO₃. The Tauc plot illustrates that the samples have a direct optical transition. The divalent cation substitution (Co²⁺ and Ni²⁺) decreases the optical band gap of NdFeO₃, leading to the recommendation of using the samples Nd_0.90Co_0.10FeO₃ and Nd_0.90Ni_0.10FeO₃ in photocatalysis of dye degradation from water. The removal efficiencies of Cr⁶⁺ at pH = 6 are 88.06 %, 85.54 %, and 85.52 % for the samples NdFeO₃, Nd_0.90Co_0.10FeO₃, and Nd_0.90Ni_0.10FeO₃, respectively. The Freundlich isotherm mode is the best-fit model for NdFeO₃ to adsorb Cr⁶⁺ ions from aqueous solutions.

In this research work, sol-gel technique was employed to prepare the strontium based spinel ferrite nanoparticles (SrFe₂O₄) with different ratios of terbium (Tb). Different characterization techniques were used to investigate the structural, morphological, dielectric and magnetic properties of the prepared samples. X-ray diffraction (XRD) result suggests that face-centered cube spinel nanocrystalline structure is formed. Crystallite size of the SrFe₂O₄ decreases with rising of Tb ratio. The morphology, shape and size of the SrFe₂O₄ were examined by scanning electron microscopy (SEM) analysis and results reveal inhomogeneous distributions of the nanostructures with high agglomeration. The electrical resistivity of the SrFe₂O₄ increases with rising of Tb ratio, which is confirmed from the cyclic voltammetry. It is observed that dielectric constant of all the samples decreases with increasing the frequency range. It is determined that the dielectric constants of the spinel ferrites are frequency dependent and decrease with increasing the frequency of applied electric field. The magnetic behavior of SrFe₂O₄ with different ratios of Tb was studied and it is found that the saturation magnetization values of samples decrease with increase in the substitution of Tb³⁺ at octahedral sites for Fe³⁺. This decrease in the values of M_s is also attributed to spin at surface of nanoparticles.

The integration of surface filtration and catalytic decomposition functions in catalytic bags enables the synergistic removal of multiple pollutants (such as dust, nitrogen oxide, acid gases, and dioxins) in a single reactor, thus effectively reducing the cost and operational difficulties associated with flue gas treatment. In this study, Mn–Ce-Sm-Sn (MCSS) catalysts were prepared and loaded onto high-temperature resistant polyimide (P84) filter through ultrasonic impregnation to create composite catalytic filter. The results demonstrate that the NO conversion rates of the composite catalytic filter consistently achieve above 95 % within the temperature range of 160–260 °C, with a chlorobenzene T₉₀ value of 230 °C. The ultrasonic impregnation method effectively loaded the catalyst onto the filter, ensuring high dispersion both on the surface and inside the filter. This increased exposure of catalyst active sites enhances the catalytic activity of the composite catalytic filter. Additionally, increasing the catalyst loading leads to a gradual decrease in permeability, an increase in pressure drops and the long residence time of the flue gas, thereby improving catalytic activity. Compared to ordinary impregnation methods, ultrasonic impregnation improves the bonding strength between the catalyst and filter, as well as the permeability of the composite catalytic filter under the same loading conditions. Overall, this study presents a novel approach to prepare composite catalytic filter for the simultaneous removal of NO and chlorobenzene at low temperatures.

The magnetization dynamics of lanthanide coordination compounds are fundamentals governing their potential applications such as information storage or molecular switches. Herein, two two-dimensional coordination polymers [Er(CA)_1.5(bpy) (DMF)]_n (1) and [Er(CA)_1.5(phen) (DMF)]_n (2) (H₂CA = 2,5-dichloro-3,6-dihydroxy-p-quinone, bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline) were synthesized and fully characterized. By the irradiation of ultraviolet light, 1 and 2 were converted to 1a and 2a which contain light-generated radicals, inducing an increase of χ_MT at room temperature. A detailed study of the dynamic magnetic property shows that the magnetization dynamics observed for 1 and 1a are dominated by Raman process, but Orbach and Raman processes are observed in 2 and 2a. The structural factors influencing the magnetic properties of this photomagnetic system are discussed.

A new class of phosphor samples, denoted as Ba_1–xAl₂Ge₂O₈:xEu²⁺ (BAGO:xEu²⁺) was synthesized using Pechini-type sol–gel technique and subsequently underwent thermal reduction in CO atmosphere. The morphology and structural characteristics of both the BAGO host lattice and the Eu²⁺ ions activated BAGO phosphors were investigated through field-emission scanning electron microscopy and X-ray diffractometry analyses, respectively. The BAGO host lattice has micro-sized particles and the Rietveld refinement reveals the presence of a monoclinic crystal phase, characterized by the space group I12/c1 (No. 15). Introducing Eu²⁺ ions into Ba²⁺ sites under CO conditions reduces the particle size, switching from micrometer to nanoscale. Within the near-ultraviolet spectrum (353 nm), the BAGO:xEu²⁺ phosphors exhibit a broadband blueish-green photoluminescence (PL) emission characterized by a peak band at 492 nm. This phenomenon is attributed to the 4f⁶ 5d¹ → 4f⁷ electronic transition. The BAGO:0.02Eu²⁺ phosphor sample exhibits the strongest bluish-green PL emission, and a comprehensive description of the concentration quenching mechanism between Eu²⁺ ions is revealed. Additionally, the thermal stability of the optimized BAGO:0.02Eu²⁺ phosphor was investigated, and its activation energy was estimated. Therefore, the synthesized bluish-green BAGO:0.02Eu²⁺ phosphor holds the promise of being a novel and promising candidate for utilization in white-light-emitting diode applications.