Study on the Formation of Crystalline Rare Earth Carbonates from Rare Earth Ore Leaching Liquors

The crystalline precipitate of rare earth carbonates has been produced by the ammonium bicar- bonate precipitation method in the recovery of RE from the ammonium sulfate leaching liquor of the weath- ered leach-deposited rare earth ore.Various influencing factors such as time,temperature and reagent con- centration have been studied.And chemical analysis,XRD,SEM,IR spectrography,TGA and DTA have been used to analyze and examine the crystalline RE carbonates.Good results were obtained.

Synthesis of Heterometallic Rare Earth(Ⅲ)-Cobalt(Ⅱ)Complexes and Their Application in Alternating Copolymerization of Cyclohexene Oxide and Carbon Dioxide

Comprehensive Summary Four heterometallic rare earth(Ⅲ)-cobalt(Ⅱ)complexes(rare earth=Y(1),Sm(2),Nd(3),La(4))stabilized by an o-phenylenediamine-bridged tris(phenolato)ligand(L)have been synthesized and characterized.In these tetranuclear complexes,one polydentate L coordinates to one rare earth(Ⅲ)ion,and one cobalt(Ⅱ)ion,respectively,while two rare earth ions are bridged by four acetate groups.These complexes were applied in the copolymerization of cyclohexene oxide and CO_(2),which showed good activity(TON up to 440)and high poly(cyclohexene carbonate)selectivity(>99%).Kinetic studies determined the equation as rate=k[CHO]1[CO_(2)]0[initiator]1,which proves a first-order dependence on initiator concentrations and implies a synergistic mechanism with rare earth and cobalt ions cooperating in epoxide ring-opening and chain propagation.

Optimization of rare earth carbonate reactive-crystallization process based on response surface method

Rare earth carbonate precipitation is mainly amorphous,of large volume and difficult to filter.To prepare crystalline rare earth carbonate,mother liquor of heavy rare earth was taken as research object,and the experimental scheme was designed based on the response surface central composite design(CCD)method.The concentration of mother liquor,aging time and seed crystal dosage were taken as independent variables,and the particle size of rare earth carbonate was taken as the response value to establish a quadratic polynomial numerical model to optimize the reactive-crystallization process of rare earth carbonate.The results show that these three factors have significant effect on the particle size of rare earth carbonate,and the influence order is mother liquid concentration>aging time>seed crystal dosage.Moreover,the interaction between mother liquor concentration and seed crystal dosage has a significant effect on the size of rare earth carbonate particles.The optimal parameters predicted by the model are as follows:the concentration of mother liquid is 1.75 g/L,seed crystal dosage is 13.56 wt%,and aging time is 8 h.Under these conditions,the predicted particle size is 28.74μm,and the experiment particle size is 28.23μm,between both,the relative error is 0.73%,which indicates that the established response surface model has a good prediction effect and a certain practical significance to guide the reactive-crystallization process of rare earth carbonate.The obtained rare earth carbonate has a crystallinity of 97.82%,uniform particles size,and low-hydrated crystals with a tengerite structure.

Behavior of sulfate in preparation of single light rare earth carbonate by Mg(HCO_(3))_(2) precipitation method

The precipitation of the water-leaching solution of Baotou mixed rare earth(RE) concentrate roasted with sulfuric acid using ammonium bicarbonate for producing RE carbonate produces a mass of ammonia-nitrogen wastewater because of the relatively low solubility of rare earth sulfate.To solve the serious problem of ammonia-nitrogen pollution,new precipitators need to be developed urgently so as to meet the requirements of environmental protection and impurities content of the product(SO_(4)^(2-)<1.8 wt% in RE carbonates products).In this paper,we studied the effects of feeding modes on the behavior of SO_(4)^(2-) during the preparation of light RE carbonate(RE=La,Ce,Pr,Nd) from their sulfate solutions using Mg(HCO_(3))_(2) as a precipitant.The results indicate that the contents of SO_(4)^(2-) in the La and Ce precipitates using positive feeding mode exceed 16 wt% because of the formation of La_(2)(CO_(3))2.15(-SO_(4))0.85·4 H_(2)O and Ce_(2)(CO_(3))_(2).15(SO_(4))0.85·3H_(2)O,while those of the Pr and Nd precipitates are 4 wt%-5 wt% since they exist in the form of n-carbonate.The precipitates prepared using synchronous feeding mode are all RE carbonate with only 4 wt%-5 wt% of SO_(4)^(2-) enclosed in the precipitation.The content of SO_(4)^(2-) in the RE carbonate obtained using reverse feeding mode is the lowest.Among them,the content of SO_(4)^(2-) in La precipitate is only 1.40 wt%.Both synchronous and reverse feeding modes can effectively reduce the content of SO_(4)^(2-)in RE carbonate,which provides theoretical guidance for the preparation of qualified light RE carbonate products by Mg(HCO3)2 precipitation method.

An in-depth multi-technique characterization of rare earth carbonates-RE_(2)(CO_(3))_(3)·2H_(2)O-owning tengerite-type structure

The present study has been conducted to contribute,once and for all,filling the lack of structural information for the whole class of rare earth(RE)carbonates owning the tengerite-(Y)structure.A complete structural characterization,carried out by Rietveld refinement of X-ray powder diffraction(XRD)data,was comparatively performed for the first time on several hydrated RE carbonates,having the general chemical formula RE_(2)(CO_(3))_(3)·χH_(2)O,RE=Y,Gd,Tb,Dy,Ho and Er.All samples share the same space group and lattice parameters similar to tengerite-(Y);the structures are also closely related,consisting in all cases of a three-dimensional framework of nine-fold coordinated RE atom polyhedral,linked together by carbonate ions.In addition to relatively minor changes in fractional coordinates of atom sites and corresponding interatomic distances,the only perceivable difference lies in the lattice parameters affected by the ionic radius of RE^(3+).However,in the case of Er,which has the lowest cationic radius among the analyzed RE,the stabilization of tengerite structure is at its limit condition,because the carbonate groups are heavily distorted.Furthermore,FT-IR and Raman spectra confirm the main structural features obtained by Rietveld refinements.The observed morphology of the various samples is almost the same,being characterized by the presence of bidimensional rod-like particles grouped in agglomerates,typical of tengerite crystals,thus indicating that the crystallization mechanism occurring during the hydrothermal synthesis is the same,irrespective of the involved RE cation.

Preparation of Ce-TiO_2/carbon aerogel electrode and its performance in degradation of 4-chlorophenol

Ce-TiO2/CA（carbon aerogel） electrode was prepared by sol impregnation approach. The XRD（X-ray diffraction） and Raman spectra reveal that the TiO2 is anatase. The UV-vis diffuse reflectance spectra show that the optical absorption edge for Ce-TiO_2/CA is red-shifted to 535 nm compared with TiO_2/CA. Under visible light irradiation, the photocurrent density increment on Ce-TiO_2/CA is 75 times that on Ce-TiO_2/FTO（fluorine-doped tin oxide）. The electrochemical impedance spectroscopy reveals that the conductivity of CeTiO_2/CA is much better than the Ce-TiO_2/FTO. Furthermore, the Ce-TiO_2/CA can be used to the highest electrosorptive photodegradation for 4-chlorophenol wastewater degradation, which is ascribed predominantly to the efficient reduction of electron-hole pair recombination in the photocatalysts.