Study on Roasting Decomposition of Mixed Rare Earth Concentrate in CaO-NaCl-CaCl_2

The decomposed process of bastnaesite, monazite and mixed rare earth concentrate in CaO-CaCl-CaCl2 was studied by means of TG-DTA method. The relationship among decomposition ratio, roasting temperature, and CaO-NaCl addition was studied by the quadratic regression orthogonal analysis, and then the regression equation was obtained. Through analysis, the optimum process conditions of mixed rare earth concentrate decomposed by CaO-CaCl-CaCl2 were obtained as follows: roasting temperature: 700℃, CaO addition: 15%, NaCl-CaCl2 addition: 10%, roasting time: 60 min, the decomposition ratio: 91.3%.

DNA Damage Effect of Mixed Rare Earth Changle Crossing Placenta Barrier on Rat Embryo

To assess the potential risk of mixed rare earths Changle for human embryo we used transplacental micronucleus test and single cell gel electrophoresis (SCGE) technique to detect DNA damage of embryo. The rats were administered respectively 0.3, 2, 5 and 20 mg·kg -1 mixed rare earths Changle every day orally from 6th to 18th day after pregnancy. The results show that the number of cells with micronucleus significantly increases as compared with the control except 0.3 mg·kg -1 group, which appears to be a dose effect relationship. The number of comet star cell greatly increases with increasing contamination dose as compared with the control except 0 3 mg·kg -1 group, and also displays a dose effect relationship. In conclusion, though mixed rare earth Changle is restricted by placenta membrane to enter embryo body, and more than 2 mg·kg -1 mixed rare earth Changle may cross placenta barrier and cause DNA damage of hepatocyte and developing erythrocyte of rat embryo.

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.

Effect of mixed rare earth and Sr on microstructure and brazability of Al-20Cu-5Si-2Ni filler metal

The objective of this study is to investigate the influence of adding tiny amount of mixed rare earth （ La, Ce） and Sr to Al-20Cu-SSi-2Ni filler metal, by analyzing the microstructure, wettability and mechanical properties of brazed joints. The results show that with the addition of mixed rare earth （La, Ce ） into Al-2OCu-SSi-2Ni alloy, the α-Al solid solution as well as CuAl2 （ Ni） intermetallic compound phase significantly reduced, while more Al-Si eutectic phase and AI-Si-Cu ternary eutectic phase were produced. And as mixed rare earth （La, Ce ） added in, the wettability of Al-2OCu-SSi-2Ni filler metal decreased, while the shear strength of the brazed joints increased. The addition of Minor Sr modificated Al-2OCu-SSi-2Ni filler metal, further reduced the CuAl2 （ Ni ） intermetallic compound phase, which was partially replaced Al-Si-Cu ternary eutectic phase. As a result, the tensile strength as well as the wettability of the filler metal was improved.

Kinetic of Dissolved Phosphorus from Calcination Products of Mixed Rare Earth Minerals

The products of mixed rare earth minerals containing monazite and bastnaesite calcined by CaO-NaCl-CaCl2 contained calcium phosphate and phosphorite. In this paper, HCl-H3cit solution was used to wash the calcination products, and the kinetic character of dissolved phosphorus was studied. The results showed that the reaction rate control changed from chemical reaction control mode to mixed control mode and diffusion control mode with increasing temperature, and the activation energy were 7.36, 27.64 and 61.27 kJ·mol-1, respectively. The change of temperature, the reagent concentration and stirring speed were studied in order to increase the dissolution rate of phosphorus. Phosphorus and rare earth in the calcination products could be separated in this process applicable to the rare earth recovery in phosphorite containing the rare earth.

Barrier Effect of Placenta Membrane of Pregnant Rat on Mixed Rare Earth Changle

To assess the potential health risks of mixed rare earths Changle for human embryo, whether it crosses placenta membrane or placenta barrier should be determined. In order to arrive at the aim placenta tissue was observed after contamination with optical and electron microscope to show distribution and destiny of mixed rare earth Changle in placenta tissue. Meanwhile the amount of rare earths in serum of pregnant rat, amniotic fluid and extract of embryo tissue were measured by using Inductively Coupled Plasma Mass Spectrometer (ICP MS). The rats were administered to 0 3, 2, 5 and 20 mg·kg -1 mixed rare earths Changle every day, respectively by oral from the 6th to 18th day after pregnancy. The results show that many particles are found in syncytiotrophoblast around capillaries of placental villi in contaminated groups under light microscope, and there are more particles following increased dose. It also was observed that some dense bodies with the envelope in placenta membrane and to difference extent damages the mitochondria crista within syncytiotrophoblast cytoplasm in contaminated groups under transmission electron microscope (TEM). Results of ICP MS assay indicate that the level of Ce increases with contamination dose in the serum of pregnant rats, and the level of total rare earth element remarkably rises in amniotic fluid and serum of pregnant rats for 20 mg·kg -1 group as compared with the control without change for the other groups.

Growth of Mixed Rare Earth Tartrate Crystals (Y_(1-x)Sm_x)_2(C_4H_4O_6)_3·zH_2O from Silica Gels

Experiments performed on the grwth of mixed crystals of rare earth tartrates (Y1-xSmx)2 (C4H4O6)3.zH2O (0≤x≤1) from silica gels at 35~40℃ and 25~30℃ employing single-diffusion technique. are discussed. The crystals maintain spherulitic morphology, irrespective of the value of x, concentration of upper and lower reactants, gel pH, gel age and gel temperature. Formation Of Liesegang rings in this system is a temperature dependent phenomenon. It is shown that with the increase of the value of x the system passes from Liesegangring phenomenon to singlezone phenomenon. Operative mechanism of crystallization in the higher (35~40℃) and lower temperature ranges (25~30℃) is explained. Seeded growth experiments indicate the possibility of increasing the size of the spherulites in the gel medium

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.

Bifunctional mixed rare earth solid catalyst for biodiesel production from acid palm oil

Solid mixed rare earth catalysts(MREEs)were synthesized by co-precipitation of raw mixed rare earth hydroxide cake obtained from monazite ore processing at different pH values(6,7 and 12).The wavelength dispersive X-ray fluorescence spectroscopy(WDXRF)results show that MREEs catalyst coprecipitated at pH 12 contain high contents of active Ce,Nd,La and Y for facilitating both esterification and transesterification reactions.The synthesized MREE by co-precipitated at pH 12 and calcined at300℃possess high amounts of Lewis basic and acidic sites,allowing it to act as bifunctional catalyst.The catalyst shows high catalytic activity for the accelerating of the initial reaction rate and converting triglycerides/free fatty acid(FFA)into fatty acid methyl ester(FAME)in both esterification and transesterification reactions.Under the reaction conditions of 3 wt%catalyst,20:1 methanol/oil molar ratio,200℃reaction temperature,3.9 MPa reaction pressure and 600 r/min stirring rate,FAME conversion reaches 99.57%in 180 min of reaction time.

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℃.

Effects of mixed rare earth fertilizer on yield and nutrient quality of leafy vegetables during different seasons

Using Chinese cabbage and rape as test material and examining the same soil conditions at different seasons（spring and autumn）, the effects of mixed rare earth fertilizer on the yield and nutrient quality of leafy vegetables were studied to provide a theoretical basis for the application of mixed rare earth fertilizer in agriculture. Results showed a seasonal difference in the nutrient quality of Chinese cabbage and rape. For crops planted in autumn, the soluble sugar and vitamin C content were higher, the titratable acid and nitrate content were lower, and the sugar acid ratio was higher relative to crops planted in spring. Mixed rare earth treatments promoted growth of both crops during both seasons. The plot yield, stem and leaf fresh and dry matter weight, and dry and fresh ratio increased. These increases for Chinese cabbage were greater in autumn than in spring while for rape, the increases were greater in spring than autumn. The soluble sugar content, titratable acid content and sugar acid ratio were increased and the nitrate content decreased, in autumn the effects were more obvious than in spring. In spring, the vitamin C content was increased, and the increase was greater for Chinese cabbage than rape. In autumn, the vitamin C content decreased, and the decrease was greater for rape than Chinese cabbage. At the same time, the content of heavy metals such as Cu, Zn, Cd, Pb and Ni in stems and leaves decreased. This decrease was greater in spring for Chinese cabbage and in autumn for rape.

Preparation of mixed rare earths modified chitosan for fluoride adsorption

This paper described the fluoride removal from water using a new adsorbent namely mixed rare earths modified chitosan （CR）. Mixed rare earths mainly contained La followed by Ce which was analyzed by inductively coupled plasma mass spectrometry （ICP-MS）. La（III）-modifled chitosan （CL） was also prepared as control. For the batch technique, the effects of various parameters such as contact time, pH, adsorbent dose, initial fluoride concentration and co-ions on fluoride adsorption were studied. Fourier trans- form infrared spectroscopy （FTIR） and X-ray diffraction （XRD） were used to characterize adsorbents. It was observed that the fluo- ride adsorption capacity of CR （3.72 mgF-/g） was higher than CL （3.16 mgF-/g） at 2 h. The presence of co-ions such as bicarbonate and carbonate greatly affected the fluoride adsorption from water. Characterization experiments indicated the successful chelation between mixed rare earths and chitosan. The possible fluoride adsorption mechanism of CR was explained by a chemical reaction.

Kinetics of mixed rare earths minerals decomposed by CaO with NaCl-CaCl_2 melting salt

For increasing reaction rate and reducing decomposing temperature,TG-DTA,XRD,SEM and Chemical analysis were used to study the kinetics of mixed rar e earths minerals decomposed by CaO with NaCl-CaCl2. The results showed that the reaction rate increased with increasing of NaC-CaCl2 addition,CaO addition,an d decomposition temperature. The kinetics of mixed rare earths minerals decompos ed by CaO conformed to 1-2/3X-(1-X) 2/3=kdt mode. The decomposition reaction rate was controlled by two steps,and the activation energy was decreased with addin g of NaCl-CaCl2 melting salt. The micro-pattern of products was loosening and po rous with NaCl-CaCl2 in decomposition system.

Decomposition of the mixed rare earth concentrate by microwave-assisted method

A novel process was proposed to strengthen the decomposition of the mixed rare earth concentrate by utilizing the microwave radiation.Mineralogical information on the mechanisms by which microwave heating improved the leaching behavior of rare earth elements（REEs）,and an interpretation of the interrelationship between mineralogy,decomposition process,and leaching process were provided in this study.The influences of the temperature,time of microwave heating and contents of NaO H（mass ratio of NaO H to mixed rare earth concentrate）on the decomposition of mixed rare earth concentrate were investigated.The results revealed that the temperature was the main factor affecting the decomposition process.The recovery of REEs by hydrochloric acid leaching reached 93.28% under the microwave heating conditions：140 oC,30 min and 35.35% NaO H.The BET specific surface area and SEM analysis indicated that the particles of mixed rare earth concentrate were non-hole,while the particles presented a porous structure after heating the concentrate by microwave radiation.For the microwave treated sample after water leaching,the BET specific surface area was 11.04 m^2/g,which was higher than the corresponding values（6.94 m^2/g）for the mixed rare earth concentrate.This result could be attributed to the phase changes of bastnaesite and monazite,and a number of cracks induced by thermal stress.The increase of BET specific surface area resulted in an increase of the recovery of REEs by promoting interaction within the system of acid leaching.

Roasting decomposition of mixed rare earth tailings by CaO in reducing atmosphere

In Baotou rare earth tailings ore, the grade of rare earth is close to that of the raw ore nearly. The rare earths are discarded in tailings dam caused by a serious waste of resources. First of all, the decomposition products of bastnaesite-and monazite-mixed rare earth tailings in CaO in reducing atmosphere were studied by means of X-ray diffraction（XRD）. The results show that the normal products are CeO2, Ce2O3, Ca5F（PO4）3, and Ce（0.75）Nd（0.25）O（1.875）, and there are no REPO4 and REFCO3.Secondly, the roasted product was extracted in HCl, and the relationship among roasting time,roasting temperature,CaO addition, and extraction temperature was studied by the quadratic regression-orthogonal analysis. Through analysis, the optimum process conditions of mixed rare earth tailings extracted are obtained as follows： roasting time of 60 min, roasting temperature of 800℃, CaO addition of 30%, extraction temperature of 80℃, and extraction ratio of 99.18%.

Ce_(1–x)La_xO_y solid solution prepared from mixed rare earth chloride for soot oxidation

Ce_（1–x）La_xO_y solid solution was simply prepared using mixed rare earth chloride（RECl_3·x H_2O, RE=Ce, La99%, containing unseparated Ce and La from rare earth metallurgical industry） as precursor by ultrasonic-assisted co-precipitation method with different ultrasonic frequencies（CLf, f=200, 400, 600, 800, 1000 Hz）. A compared Ce_（1–x）La_xO_y solid solution（CL＊） was also prepared by the same mothod with 10% less precipitant. X-ray diffraction results confirmed the formation of Ce1–xLaxOy solid solution, and the crystal structures of these catalysts were not very sensitive to ultrasonic frequency and precipitant amount. However, both of the factors had obvious effect on morphology and surface area of CL, and precipitant amount seem to play a more crucial role than ultrasonic frequency for Ce_（1–x）La_xO_y solid solution preparation. When soot and catalyst were tight contacted, the peak temperature（Tpeak） of soot oxidation and oxygen reducing temperature for CLf catalysts decreased linearly with increasing surface area. Under loose contact condition, the Tpeak had obvious negative correlation with H_2 consumption. It was inferred that good reducibility of the Ce_（1–x）La_xO_y solid solution favored the soot oxidation reaction. The Ce_（1–x）La_xO_y solid solution prepared from unseparated rare earth chloride showed a good soot oxidaiton activity. Controlling the preparation conditions to prepare a CL catalyst would high surface area will enhance its reducibility and activity.

Study on Simultaneous Catalytic Reduction of Sulfur Dioxide and Nitric Oxide on Rare Earth Mixed Compounds

CeO2/γ-Al2O3, La203/γ-Al2O3, CeO2-La203/γ-Al2O3 and CeO2-La2O3, which were prepared by impregnating in certain ratio, were used as the catalysts for the reduction of SO2 and NO by CO. Separate and simultaneous removal of SO2 and NO over LaEO3/γ-Al2O3, CeOE/γ-Al2O3, CeOE-LaEO3/γ-Al2O3 were investigated. The phase characteristics of catalysts were also analyzed by X-ray diffraction. The result shows that the conversions of SO2 and NO are above 98 % over CeOE/γ-Al2O3 and CeOE-LaEO3/γ-Al2O3. After SO2 is added in the NO-CO-N2 system （NO ：SO2 = 1：2 - 1 ： 3）, the conversions of SO2 and NO are both above 98%. Furthermore, it is found that CeO2-La2O3 with various ratios has different activity for the simultaneous reduction of SO2 and NO.

Research on toughening mechanisms of alumina matrix ceramic composite materials improved by rare earth additive

Mixed rare earth elements were incorporated into alumina ceramic materials. Hot-pressing was used to fabricate alumina matrix composites in nitrogen atmosphere protection. Microstructures and mechanical properties of the composites were tested. It was indicated that the bending strength and fracture toughness of alumina matrix ceramic composites sintered at 1550 ℃ and 28 MPa for 30 min were improved evidently. Besides mixed rare earth elements acting as a toughening phase, AlTiC master alloys were also added in as sintering assistants, which could prompt the formation of transient liquid phase, and thus nitrides of rare earth elements were produced. All of the above were beneficial for improving the mechanical properties of alumina matrix ceramic composites.

Luminescent Properties of Bi-Rare Earth Complexes with m-methylbenzoic Acid and 1,10-phenanthroline

The bi rare earth complexes EuTb( m MBA) 6(phen) 2·2H 2O, TbY( m MBA) 6(phen) 2·2H 2O were synthesized by the reaction of RECl 3 with m methylbenzoic acid and 1,10 phenanthroline in ethanol solution, where m MBA=m methylbenzoate and phen=1,10 phenanthroline. The luminescence properties of the title complexes were studied in comparison with the corresponding complexes Eu 2( m MBA) 6(phen) 2·2H 2O and Tb 2( m MBA) 6(phen) 2·2H 2O respectively. The results indicate that the emission intensity from europium ion can be greatly enhanced by the terbium ion, while the emission from terbium ion was strongly quenched by europium ion in EuTb( m MBA) 6(phen) 2·2H 2O; the emission intensity from terbium ion can be greatly enhanced by yttrium ion in TbY( m MBA) 6(phen) 2·2H 2O. The mechanism about the results was discussed.

Effect of Rare Earth Elements on Isothermal Transformation and Microstructures in 20Mn Steel

The effect of rare earth elements on the isothermal transformation and microstructures in 20Mn steel is in- vestigated by means of metallography and dilatometry.Rare earth elements decrease both the incubation period of pro-eutectoid ferrite and the rate of pearlitic transformation.In addition,rare earth elements play a role of reducing needle-like ferrite and the amount of pearlite,densifing the lamellar space of pearlite and enhcing segregation of carbide in granular bainite.It is suggested that rare earth elements may decrease the interfacial energy of grain boundary and interphase,hinder the diffusion of carbon atoms and form rare earth carbides with high melting point which reduce the carbon content in austenite.