Study on Escaping Fluorine Inhibition in Calcining Process of Mixed Rare Earth Concentrate

GC technology was used to study escaping fluorine in calcined process of mixed rare earth concentrate. The mixed rare earth concentrate and it adding assistant of CaO-NaCl-CaCl2 were calcined at 400～750 ℃ for 30～120 min, and then total amount of fluorine, exhausting ratio of fluorine, decomposition ratio and the component were determined. The results showed that adding CaO-NaCl-CaCl2 the decomposition ratio was up to 90% at 700 ℃ in 1 h, and the escaping ratio of fluorine decreased from 29.52% to 0.948%. The average inhabitation ratio was 98.39%. This method supplied basis for low energy and clean decomposition of mixed rare earth concentrate.

Study on Roast Reaction Kinetics of Baotou Concentrate of Rare Earth with 15% Na_2CO_3 Additions

The research on the mechanism of the roast reaction of Baotou concentrate of rare earth with 15% Na 2CO 3 additions was carried out through thermal, X ray diffraction and chemical analysis. Bastnaesite(RECO 3F) was first decomposed into REOF at 623～741 K, then Monazite(REPO 4) reacted with Na 2CO 3 was decomposed into RE 2O 3 and produced Ca 8Nd 2(PO 4) 6O 2 at 853～928 K. The kinetics parameters of the roast reaction were calculated. The results of the calculation were as follows: at 623～741 K, E =152 kJ·mol -1 , n =0 77, A =1 11×10 12 s -1 ·mol -1 , k =1 102( T =705 K), and at 853～928 K, E =232 kJ·mol -1 , n =1 16, A =1 11×10 9 s -1 ·mol -1 , k =1 07×10 -4 ( T =915 K). The equation of the mechanism of the roast reaction is F 1=-ln(1- α ) at 623～741 K and 853～928 K according to TG curves.

Acidity and Rare Earth Concentration Effects on Ytterbium Purification by an Electrolysis Reduction in H_2SO_4 Medium

Ytterbium purification by an electrolysis reduction in sulfuric acid medium was investigated without nitrogen or argon protection, in which Ru-Ir-Ti alloy nets and mercury were used as anode and cathode, respectively. How the conditions such as the acidities of cathode and anode solutions, and the concentration of Yb（ Ⅲ ） to affect the circuit and ratio of Yb（ Ⅱ ）/Yb （ Ⅲ ） in electrolysis reduction were studied.

Flotation-Calcination-Magnetic Separation Hybrid Process for Concentration of Rare Earth Minerals Contained in a Carbonatite Ore

A hybrid process consisting of flotation and magnetic separation has been developed to concentrate multi-phase rare earth minerals associated with a carbonatite ore that contains a significant amount of niobium. The deposit is known to contain at least 15 different rare earth minerals identified as silicocarbonatite, magnesiocarbonatite, ferrocarbonatites, calciocarbonatite, REE/Nb ferrocarbonatite, phosphates and niobates. Although no collector exists to float all the different rare earth minerals, the hydroxamic acid-based collectors have shown adequate efficiency in floating most of these minerals. 92% recovery of total rare earth oxide (TREO) and niobium in 45% mass was possible at d80 of <65 microns grind size. It was also possible to reduce the mass pull to 28%, but TREO and Nb’s recovery dropped to 85%. Calcination of the concentrate followed by quenching and fine grinding to <25 μm allowed upgrading the flotation concentrate by magnetic separation. It was demonstrated that at least 87% TREO and 85% Nb could be recovered in 16% of the feed mass. The paper discusses the overall concept of the flowsheet and the experimental strategies that led to this process.

Selective leaching of calcium from mechanically activated mixed rare earth concentrate

The loss of rare earths(REs)takes place during the pre-decalcification process of mixed rare earth concentrate.In an effort to reduce such RE loss,a novel idea to improve the leaching selectivity of Ca to REs by applying selective mechanical activation was proposed.First,regarding the key minerals affecting the leaching selectivity of Ca to REs,the differences in the mechanical activation behaviors of CaF_(2) and REFCO_(3) were studied,and we find that the lattice strain of CaF_(2) increases from 0.21%to 0.42%,whereas that of REFCO_(3) increases from 0.31%to 0.40%.Notably,CaF_(2) demonstrates a larger lattice strain than REFCO_(3),indicating greater mechanical activation energy storage and higher leaching activity.Next,the HCl leaching process was studied.A significant leaching selectivity of Ca to REs,from 21.6 to 35.1,is achieved through mechanical activation.The Ca leaching rate reaches 80.7%when the RE loss is 2.3%in the activated sample.This study provides an novel approach for achieving selective extraction of specific components via mechanical activation pretreatment.

Decomposition of bastnasite and monazite mixed rare earth minerals calcined by alkali liquid

The process of decomposion of the bastnasite and monazite rare earth concentrates by alkali solutions was investigated. The mixed slurries of the rare earth concentrates and the alkali solutions were calcined at different temperatures in a rotary tubular electric furnace. The effects of calcination temperature on the decomposing ratio of rare earth, the oxidation ratio of cerium, the stripping of fluorine and phospho-rous after calcinations, and the adaptability of the process to the mixed rare earth concentrates of different grade were studied. The results showed that the decomposition ratio of rare earth and the oxidation ratio of cerium could reach 95.8% and 93.7%, respectively, while the cal-cinating temperature was above 300℃.

High temperature dephosphorus behavior of Baotou mixed rare earth concentrate with carbon

Based on the carbothermal reduction technology applied in industry,the dephosphorization behavior of Baotou mixed rare earth concentrate(Baotite) with carbon at high temperature was investigated.The experimental results showed that both the charred coal and the coking coal were effective carbonaceous reductants for the dephosphorization of the Baotite.Among them,the charred coal was more suitable for the dephosphorus due to its high carbon content and lower volatile and ash.When the rare earth pellets,made by pressing the mixture of the Baotite,charred coal and water in mould,were roasted at 1500 oC for 2 h,its dephosphorus rate was as high as 98%.Roasting temperature was a main factor for the dephosphorus rate,and roast time was the second one.The size of both charred coal and coking coal also had influence on the dephosphorus,and was better less than 150 μm.

Decomposition of mixed rare earth concentrate by NaOH roasting and kinetics of hydrochloric acid leaching process

A new clean extraction technology for the decomposition of Bayan Obo mixed rare earth concentrate by NaOH roasting is proposed.The process mainly includes NaOH roasting to decompose rare earth concentrate and HCl leaching roasted ore.The effects of roasting temperature,roasting time,NaOH addition amount on the extraction of rare earth and factors such as HCl concentration,liquid-solid ratio,leaching temperature and leaching time on the dissolution kinetics of roasted ore were studied.The experimental results show that when the roasting temperature is 550℃and the roasting time is 60 min,the mass ratio of NaOH:rare earth concentrate is 0.60:1,the concentration of HCl is 6.0 mol/L,the ratio of liquid to solid(L/S)6.0:1.0,and the leaching temperature 90℃,leaching time 45 min,stirring speed 200 r/min,and the extraction of rare earth can reach 92.5%.The relevant experimental data show that the process of HCl leaching roasted ore conforms to the shrinking core model,but the control mechanism of the che mical reaction process is different when the leaching temperature is different.When the leaching temperature is between 40 and 70℃,the chemical reaction process is controlled by the diffusion of the product through the residual layer of the inert material.The average surface activation energy of the rare earth element is E_a=9.96 kJ/mol.When the leaching temperature is 75-90℃,the chemical reaction process is controlled by the interface transfer across the product layer(product layer interface mass transfer)and diffusion.The average surface activation energy of rare earth elements is E_a=41.65 kJ/mol.The results of this study have certain significance for the green extraction of mixed rare earth ore.

Extraction and separation of yttrium from other rare earths in chloride medium by phosphorylcarboxylic acids

Two phosphorylcarboxylic acids,3-((bis(2-ethylhexyloxy))phosphoryl)propanoic acid(PPA) and 3-((bis(2-ethylhexyloxy))phosphoryl)-3-phenylpropanoic acid(PPPA),were synthesized for separating yttrium from other rare earths in the chloride feed of ion-adsorption type rare earth concentrate.The effect of the factors such as pH_(1/2),temperature,saponification degree and phase modifiers was investigated.The separation efficiencies of PPA and PPPA are obviously better than the typical extractants such as sec-octylphenoxy acetic acid(CA-12) and naphthenic acid(NA).The extraction process of rare earths by PPA and PPPA is a cation exchanging reaction,which is similar to those of CA-12 and NA.The loaded rare earths in both PPA and PPPA systems can be effectively back-extracted by 0.5 mol/L HCl or higher concentration.A cascade extraction process for separating yttrium from other rare earths was developed using PPPA as the extractant.The yttrium product with the purity of 97.20 wt% was obtained by 35 stages of extraction and 12 stages of scrubbing.

Decomposition reaction kinetics of Baotou RE concentrate with concentrated sulfuric acid at low temperature

Baotou RE concentrate was decomposed with concentrated sulfuric acid by controlling the roasting temperature below 500℃.Thermogravimetry-differential thermal analysis（TG-DTA） and chemical analytical methods were used to study the thermal decomposition process and the thermal decomposition effect.The Freeman-Carroll method was applied to analyze the TG-DTA curves.The activation energy, reaction order, and reaction frequency factor at different stages were calculated.The Satava method was used to deduce the reaction mechanism and the relative reaction rate during the thermal decomposition process.

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 Na_(2)CO_(3)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 SiO_(2)react to form silicates,causing hardening.Further,REPO_(4)and NaF can directly generate CeF_(3) and CeF_(4)at high temperatures,and a part of CeF_(4)and NaF forms a solid solution substance Na_(3)CeF_(7).Rare earth oxides calcined at a high temperature of 750℃were separated to produce Ce_(0.6)Nd_(0.4)O_(1.8),Ce_(4)O_(7),and LaPrO_(3+x).Then,BaSO_(4),Na_(2)CO_(3),and Fe_(2)O_(3)react to form barium ferrite BaFe_(12)O_(19);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℃,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)=[-In(1-α)]^(1/3).The reaction order n reaches the minimum in the temperature range of 680-757℃,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).

The Concentration Degree of Nationwide Rare Earth Industry Increased Significantly

Since the'Twelfth Five Year Plan'period,China has made considerable progress in the organization and setup of large rare earth groups,layout of rare earth industry has become more rational,the concentration degree has increased significantly,the previously small,scattered,and chaotic situation has basically been reversed.

Upconversion 32Nb_(2)O_(5)-10La_(2)O_(3)-16ZrO_(2) glass activated with Er^(3+)/Yb^(3+) and dye sensitized solar cell application

Er^(3+)/Yb^(3+)codoped niobium pentoxide glasses were fabricated by the aerodynamic levitation(ADL)method with rapid cooling rate.All samples with various doping concentrations showed good upconversion luminescence properties under 980 nm laser excitation.The structure,transmittance spectrum,and luminescence properties of the samples were systemically investigated by XRD,UV-Vis-NIR spectrophotometer,and upconversion spectra.All transparent samples exhibited green and red upconversion emissions centered at 532,547,and 670 nm.Experimental results showed that the sample codoped with 1 mol%Er^(3+)/Yb^(3+)has the strongest upconversion emissions,and the increase of the doped Yb^(3+)concentration results in the increased red emission and reduced green emission.The logI-logP plot of green emission indicated that the green emissions reach the saturation at high pump power excitation,deviating from the low-power regime.After one-photon energy transfer(ET)process,^(4)I_(11/2)+^(4)I_(11/2)→^(4)F_(7/2)+^(4)I_(15/2) process between the two neighboring Er^(3+)ions was responsible for the population of the 4S3/2/4H11/2 states.The niobium pentoxide codoped with Er^(3+)/Yb^(3+)bulk glasses could be used in the dye sensitized solar cell(DSSC)to improve the efficiency.

Synergistic effect of crystal structure and concentration quenching on photoluminescence of Er^(3+) doped upconversion nanocrystals

YbF（2.357, YbF3, Ba2 YbF7, and Ba 2 upconversion nanocrystals doped with emitter Er^3＋ ion were synthesized in the same solvent system just with changing the molar ratio of Ba^2＋ to Yb^3＋ in the precursor, which corresponed to the crystal phases of rhombohedral, orthorhombic, tetragonal, and cubic, respectively. All the samples emitted both 660 nm red light and 543/523 nm green light which originated from Er^3＋-4f^n electronic transitions ~4F（9/2-~4I（15/2 and ~4S（3/2/~2H（11/2-~4I（15/2, respectively. It was worth mentioning that YbF 3：Er^3＋, Ba2 YbF7：Er^3＋, and BaF2：Er^3＋ could emit dazzlingly bright light even under the excitation of a 980 nm CW laser with output power of 0.1 W. Upconversion emission mechanism analysis indicated that the intensity ratio of red to green light highly depended on the synergistic effect of crystal structure, concentration quenching, and particle size, but were not sensitive to crystallinity as previously reported for NaL nF4（Ln=lanthanide.

Investigation on the amounts of Na_2CO_3 and sulphur to obtain pure Y_2O_2S and up-conversion luminescence of Y_2O_2S:Er

The process to prepare pure phase of hexagonal Y2O2S was investigated. Effect of mixed flux of Na2CO3 and S amounts was studied. The phase composition and morphology were characterized by X-ray diffraction （XRD） and scanning electron microscopy （SEM）. The results showed that the single phase of Y2O2S with smooth morphology could not be obtained as the molar ratio of Y2O3, Na2CO3 and S was in the range of 1：（0.5-1）：（2-3） until the molar ratio was increased to 1：1.5：4. Different Er3＋ concentration doped Y2O2S：Er powders were prepared with molar ratio of the raw materials 1：1.5：4. The quenching concentration of Er3＋ in Y2O2S was more than 2 mol.%, which was due to the interaction of electric quadrupoles between Er3＋ ions.

Luminescence properties of Eu^(2+) -doped Ba_3Si_6O_12N_2 green phosphor: concentration quenching and thermal stability

The efficient Eu2＋ -doped Ba3 Si6O12N2 green phosphors were prepared by a traditional solid state reaction method under N2 /H2 atmosphere at a temperature up to 1350 ℃ for 12h. Photoluminescence （PL） properties showed a broad emission band with a peak of 525 nm and the full width of half-emission maximums （FWHM） of 70 nm under 460 nm light irradiation. The X-ray diffraction patterns （XRD） and scanning electron microscope （SEM） images of the synthesized powder demonstrated its pure phase and excellent crystallization. Quenching concentration in this phosphor was found to be 0.3. The mechanisms of concentration quenching and redshift of emission peak with increasing concentration of Eu2＋ were studied. The temperature dependence measurement of this green phosphor revealed excellent thermal quenching property compared to silicate green phosphor. It is believed that Ba3 Si6O12N2 ：Eu2＋ is an excellent green phosphor for UV or blue chip based white LEDs.

Thermoelectric properties of Eu- and Na-substituted SnTe

Thermoelectric properties of spark-plasma-sintering prepared bulk materials EuxNay□zSn1–x–y–zTe above room temperature were investigated. The implementation of Eu and Na into the SnTe lattice was monitored by refinement of lattice parameters as well as energy dispersive X-ray spectroscopy（EDXS）. The binary SnTe achieved the highest ZT value of 0.63 at 786 K, and showed a hole concentration of 4.6′10^19 cm^–3 at 300 K. In comparison with pristine SnTe, the samples containing Eu had lower carrier mobility but higher Hall carrier concentration. For Eu- and Na-substituted samples, the increased hole concentration was unfavorable for the improvement of thermoelectric properties.