Dissolution behaviors of rare earth elements in phosphoric acid solutions

In order to provide practical fundamental data for rare-earth elements （REEs） recovery from phosphoric acid and to betterunderstand REEs behavior during the phosphoric acid evaporation process, the solubilities of REEs in phosphoric acid with variousconcentrations of phosphorus at different temperatures were measured. A simple linear model between REEs solubility andphosphoric acid concentration is built and the experimental data are found to fit it very well （R2〉0.94）. Hydrogen-ion concentration isfound to be the predominant factor controlling the solubility of REEs in phosphoric acid. In addition, the solubility of REEs inphosphoric acid is found to sharply decrease with increasing temperature, which can be attributed to the increase of the Gibbs energyof the REEPO4 dissolution reaction or the restraint of the disassociation of phosphoric acid molecules owing to the elevatedtemperature.

Combustion synthesis and luminescence properties of LaPO4： Eu （5%）

Rare earth doped materials are an important type of phosphors due to their excellent performance such as stability at high temperature and light emission covering the entire visible domain. The combustion synthesis at acid pH of the monoclinic LaPO4： Eu（5%） powders was described. A mixture of La（NO3）3·6H2O, EuCly6H2O and （NH4）2HPO4 was used as anion precursor and glycin as fuel. The synthesis was followed by structure, morphology characterisation and luminescent properties of the obtained compound. The room temperature emission measurements under ultraviolet excitation at 254 nm were made for the emission transition ^5D0→^7FJ of this phosphor. The CIE （Commission Intemationale de L＇Eclairage） chromatic coordinates, dominant wavelength and colour purity were determined and compared to other luminescent materials obtained by other methods.

Study on Behavior of Carbon Reduction of Monazite Concentrate

The behavior of monazite concentrate reduced by carbon, especially the decomposed procedure of rare earth phosphates, was investigated by X-ray diffraction, electron probe, TG method and chemical analysis. The results show that rare earth phosphates in monazite concentrate can be reduced to their oxides, among them the decomposition processes of cerium phosphate are not in step with lanthanum phosphate, neodymium phosphate and so on, and the phosphorus was volatilized into air in simple form.

Microwave-Assisted Synthesis of LaPO_4∶Ce, Tb and Phosphor Characterizations

A novel method was devised to prepare green phosphor of LaPO4∶Ce, Tb by the combination of co-precipitation and microwave irradiation. The effective hess of microwave as pre-treated process and after process and microwave irradiation time were mainly discussed. The formation process and structure of green phosphor of LaPO4∶Ce, Tb were characterized by TG-DTA, XRD and SEM, respectively. As a result, phosphor of monoclinic structure with widely distributed particle size about 70 nm was successfully synthesized. The effect of microwave-assisted method as pretreatment and after-treatment on the structure and luminescent was studied property. Results indicate that the after-treatment by microwave would enhance the crystallinity as well as fluorescence intensity, the fluorescence intensity increased with the time of microwave pretreatment time, the high fluorescence intensity was found at 80 min pretreatment time. Morphological structure of phosphor particles prepared by two methods seemed similar. The emission spectrum and excitation spectrum of phosphor as prepared detected by spectrophotometer showed typical luminescent of green phosphor, the luminescence mechanism was preliminarily discussed.

Mild Hydrothermal Synthesis, Characterization and Properties of Na_5Ce(PO_4)_3, Na_3Yb_2(PO_4)_3·H_2O and Na_(5-2x)Yb_2xCe_(1-x)(PO_4)_3·yH_2O

Novel phosphates, Na5-2x Yb2xCe1-x (PO4)3·yH2O(x=0-1, y=0-1), were synthesized under mild hydrothermal conditions at 240℃ with Ce(SO4)2·H2O, Ce(SO4)2·2(NH4)2SO4· 4H2O, CeO2, Yb2O3, 85 % H3PO4 and NaOH as the starting materials. The products were sensitively influenced by the pH value of the systems and reaction temperature. Under an acidic condition, CePO4 was the product at 240℃, in which Ce(Ⅳ ) species was reduced to Ce(Ⅲ) species. Under a weak basic condition, Na2Ce(PO4)2·0. 79H2O was produced. Under a medium basic condition, the expected compound Na5Ce(PO4)3 was the product. Under a basic condition, CeO2 was the final product, amorphous phase was also produced in some cases. The structure of the compounds were investigated by X-ray diffraction, SEM, IR, Raman, 31P MAS NMR and XPS spectroscopies. To determine the valence of Ce in the compound, EPR and DRS of the compound were also recorded. The thermal properties of the compounds were determined with DTA-TG analysis. Na5Ce(PO4)3 was decomposed into Na3Ce(PO4)2, Na4P2O7 and O, at 694℃, in which Ce(Ⅳ) was reduced to Ce(Ⅲ) species. Na3Yb2(PO4)3·H2O lost water and was transferred into a new phase at a high temperature 682℃. The thermal stability of Na5-2xYb2xCe1-x (PO4)3· yH2O could be improved by increasing x value. When x=0. 54, the compound was stable even at the temperature ca. 1 000℃.The ionic conductivities of the compounds were increased when the amount of Yb in the compound was increased and when x=0. 33, it reached the highest value (σ300℃= 3. 96 ×10-6 S·cm-1).

Efficient removal of phosphate from aqueous solution using novel magnetic nanocomposites with Fe_3O_4@SiO_2 core and mesoporous CeO_2 shell

Fe_3O_4@SiO_2 magnetic nanoparticles functionalized with mesoporous cerium oxide（Fe_3O_4@SiO_2@mCeO_2） was fabricated as a novel adsorbent to remove phosphate from water. The prepared adsorbent was characterized by X-ray diffractometry（XRD）, transmission electron microscopy（TEM）, nitrogen adsorption-desorption and vibrating sample magnetometry（VSM）, and its phosphate removal performance was investigated through the batch adsorption studies. Characterization results confirmed that mesoporous cerium oxide was successfully assembled on the surface of Fe_3O_4@SiO_2 nanoparticles, and the synthesized adsorbent possessed a typical core-shell structure with a BET surface area of 195 m^2/g, accessible mesopores of 2.6 nm, and the saturation magnetization of 21.11 emu/g. The newly developed adsorbent had an excellent performance in adsorbing phosphate, and its maximum adsorption capacity calculated from the Langmuir model was 64.07 mg/g. The adsorption was fast, and the kinetic data could be best fitted with the pseudo-second-order kinetic model. The phosphate removal decreased with the increase of solution pH（2 to 10）, while the higher ionic strength slightly promoted the phosphate adsorption. The presence of Cl~– and SO^（2–）_4 could enhance the adsorption of phosphate whereas HCO~–_ 3 had interfering effect on the phosphate adsorption. The adsorption mechanism was studied by analyzing Zeta potential and FTIR spectroscopy, and the results indicated that the replacement of the surface hydroxyl groups by phosphate ions with the formation of inner-sphere complex played a key role in the phosphate adsorption. The spent adsorbent could be quickly separated from aqueous solution with the assistance of the external magnetic field, and the adsorbed phosphate could be effectively desorbed using a 1 mol/L NaOH solution.

Unique capability of NdPO_(4)to activate hydrogen for efficient hydrogenation of furfural to furfuryl alcohol over Nd-Co-P composites

Efficient and applicable catalysts are highly desirable for advanced biomass transformation industry,here,we fabricated a series of Nd-Co-P catalysts for hydrogenation of furfural(FAL)to furfuryl alcohol(FOH).By comprehensive characterizations,it is demonstrated that the prepared Nd-Co-P samples are structured as(NdPO_(4))_(m)/Co_(2)P nanocomposites with molar ratio(m)in range of 0.24-1.1;by manipulating m,the outstanding catalytic efficiency comparable with the performance of precious metal catalysts,such as turnover frequency(TOF)up to 0,50 s^(-1)(being ten-fold higher than Co_(2)P)and FOH yield up to97%,is achieved on the reusable(NdPO_(4))_(m)/Co_(2)P composites.Te mperature programmed desorption(TPD),in-situ infrared spectroscopy(IR)and kinetic-mechanism studies further disclose that Co_(2)P is decisive for activating FAL,instead,NdPO_(4)possesses unique capability of activating hydrogen which readily facilitate the selective hydrogenation of FAL to FOH through a rapid Langmuir-Hinshelwood process over(NdPO_(4))_(m)/Co_(2)P catalyst.These results indicate that rare-earth phosphates like NdPO_(4)can act as the promising and reliable catalytic component to activate hydrogen,which can be of interest not only for innovating novel and applicable non-metallic catalysts for sustainable biomass transformation analogous to hydrogenation of FAL,but also for expanding material base for other green mass transformation techniques involving hydrogen.