Weathered crust elution-deposited rare earth ore is crucial source of medium and heavy rare earths,with in-situ leaching being the most common mining method.The high contents of impurity of aluminum in the leach solut...Weathered crust elution-deposited rare earth ore is crucial source of medium and heavy rare earths,with in-situ leaching being the most common mining method.The high contents of impurity of aluminum in the leach solution are a significant challenge for the subsequent enrichment process of rare earths.A comprehensive understanding of the occurrences and vertical distribution of aluminum and rare earths within typical vertical profiles can provide valuable insights into entire design of the in-situ leaching.This paper improves a five-step sequential extraction method to analyze the occurrence and vertical distribution of rare earths and aluminum in vertical profiles from Chongzuo and Longyan.Experimental results demonstrate that soil solution pH is the main factor affecting the vertical distribution of ionexchangeable rare earths.Both samples have distinct areas of enrichment for ion-exchangeable rare earths or aluminum.Ion-exchangeable rare earths are primary concentrated in the middle and lower parts of the ore layer(4-13 m in Chongzuo,14-22 m in Longyan),while the ion-exchangeable aluminum is mainly enriched in the upper part of the ore layer(1-5 m in Chongzuo,and 2-14 m in Longyan).The vertical distribution of inorganic hydroxy aluminum is likely influenced by the micromorphology and particle size of the clay minerals.The inorganic hydroxy aluminum concentration in Chongzuo samples decreases continuously from 415.65 to 120.95 mg/kg with increasing sampling depth,whereas the concentration in Longyan samples(110.55-171.27 mg/kg)is almost independence with sampling depth.These results provide direct guidance for the entire design of the injection well depth and the leaching parameters,thereby inhibiting the leaching of impurity of aluminum and lower the consumption of leaching agent.展开更多
To find a greener and more economical approach for treating the Mountain Pass rare earth concentrate(MPREC),a novel "Combination Method",including the processes of oxidizing roasting,HCI leaching and sulfuri...To find a greener and more economical approach for treating the Mountain Pass rare earth concentrate(MPREC),a novel "Combination Method",including the processes of oxidizing roasting,HCI leaching and sulfuric acid roasting,is proposed in this research.In this paper,the effect of phase transition behavior in hydrochloric acid leaching during oxidative roasting at 450-600℃ was studied.During roasting,the bastnasite in MPREC is decomposed into CeLa_(2)O_(3)F_(3) and(Ce_(0.33),La_(0.33),Ca_(0.33))O_(1.5).As the CeLa_(2)O_(3)F_(3) phase has the fluorine-fixation effect,the generated CeLa_(2)O_(3)F_(3) phase can not be dissolved by HCI after roasting at 500 and 550℃,but it can be decomposed by HCI after roasting at over 600℃,resulting in the improvement of the leaching rate of total F element.The maximum leaching efficiency of rare earth elements(REEs) can reach 70.32 wt% at the roasting temperature of 550℃.After roasting at over 600℃,some F^-ions in the solution combined with RE^(3+) to form REF_(3) precipitate and enter the leaching residue,and the others are in the form of [CeF_(3)]^+ in the leaching solution during leaching,therefore,the leaching efficiency of non-ce rium REEs decreases while that of cerium element increases.This work provides basic research for optimizing the actual production process of MPREC.展开更多
With the continuous tightening of automotive emission regulations and the increasing promotion of energy-efficient hybrid vehicles,new challenges have arisen for the low-temperature performance of three-way catalysts(...With the continuous tightening of automotive emission regulations and the increasing promotion of energy-efficient hybrid vehicles,new challenges have arisen for the low-temperature performance of three-way catalysts(TWCs).To guide the design of next-generation TWCs,it is essential to further develop our understanding of the relationships between microstructure and catalytic performance.Here,Rh/CeO_(2)–ZrO_(2) catalysts were synthesized with different Rh metal dispersion by using a combination of the wet impregnation method and reduction treatment.These catalysts included Rh single-atom catalysts,cluster catalysts,and nanoparticle catalysts.The results showed that the Rh nanoparticle catalyst,with an average size of 1.9 nm,exhibited superior three-way catalytic performance compared to the other catalysts.Based on the catalytic activity in a series of simple reaction atmospheres such as CO+O_(2),NO+CO,and hydrocarbons(HCs)+O_(2) and operando infrared spectroscopy,we found that metallic Rh sites on Rh nanoparticles are the key factor responsible for the low-temperature catalytic performance.展开更多
In acid treatment technology of Baotou mixed rare earth ore,large quantities of ammonia-nitrogen wastewater are produced in the step of ammonium bicarbonate precipitation to transform rare earth sulfate.In this paper,...In acid treatment technology of Baotou mixed rare earth ore,large quantities of ammonia-nitrogen wastewater are produced in the step of ammonium bicarbonate precipitation to transform rare earth sulfate.In this paper,we adopted a green precipitant magnesium bicarbonate(Mg(HCO3)2) to substitute ammonium bicarbonate to eliminate ammonia-nitrogen pollution.The effects of n(HCO3^-):n(RE^3+),aging temperature and aging time on the crystallization using Mg(HCO3)2 precipitation method were investigated.The results indicate that the rare earths could be completely recovered when n(HCO3^-):n(RE^3+) is higher than 3.15:1.The crystal water content of rare earth carbonates is affected by the aging temperature.The precipitate has a bad filterability when the aging temperature is over 40℃.This can be attributed to the less crystallized water molecules of the hydrated rare earth carbonate precipitation.The mixed rare earth carbonates are prone to be crystalline,and have a good filterability at aging temperatures below 40℃.Meanwhile,the evolution mechanism of crystalline mixed rare earth carbonates is reasonably deduced,the amorphous rare earth carbonates are first dissolute and then recrystallized.Under the optimized aging conditions,the purity of the crystalline precipitate meets the requirements of the fine product standard(GB/T 16479-2008).The filtrated could be used to produce Mg(HCO3)2,thus to realize the recycling of magnesium sulfate.展开更多
Rare earths(REs) are of vital importance for the development of new materials and green energy.Magnesium bicarbonate is one of the most recyclable and environmental-friendly precipitant for REs recovery from leaching ...Rare earths(REs) are of vital importance for the development of new materials and green energy.Magnesium bicarbonate is one of the most recyclable and environmental-friendly precipitant for REs recovery from leaching solutions. Nd_2(CO_3)_3 has difficulties in industrial production. So in this study,the precipitation of neodymium from chloride solution by magnesium bicarbonate are investigated. The effects of feeding method, [HCO_3^-]/[Nd^(3+)] mole ratio, feeding speed and reaction temperature on yield and impurity(magnesia) content are systematically studied. Results show that the impurity(magnesia)content decreases to 0.010 wt% with a yield approaching to 100% obtained under the conditions of[HCO_3^-]/[Nd^(3+)] = 3.00 by parallel flow addition at 50 ℃. The major impurity(magnesia) in rare earth carbonates mainly presents in the form of physical absorption, which can be easily removed by scrubbing. Therefore, it offers a promising green process that uses magnesium bicarbonate to produce neodymium carbonate due to its cycling of carbon dioxide, magnesium salt and waste water.展开更多
Solid oxide fuel cell is a promising energy conversion system which converts chemical energy into electrical energy directly. Electrolyte is the key component and determines the working temperature. In this paper,ceri...Solid oxide fuel cell is a promising energy conversion system which converts chemical energy into electrical energy directly. Electrolyte is the key component and determines the working temperature. In this paper,ceria and scandia co-doped zirconia electrolytes sintered from 1300 to 1550 ℃ were chosen as research objects. Scanning electron microscopy, X-ray diffraction and transmission electron microscopy were performed to characterize the ceramic samples. The effects of grain size and grain boundary element segregation on the electrical conductivity were focused. Electrochemical impedance spectroscopy was used to calculate the bulk, grain boundary and specific grain boundary conductivity. Results show that the bulk and grain boundary ionic conductivity increases with the increasing grain size.However, the specific grain boundary conductivity decreases with the increasing grain size. This is explained by the fact that Sc^(3+) is segregated at the grain boundary, which leads to higher oxygen vacancy concentration when sintered at lower temperature.展开更多
Two-dimensional metal oxide nanostructures,such as nanoplates,nanowalls,and nanosheets,have received further attentions in recent years,due to their outstanding properties resulted from the small thickness and quantum...Two-dimensional metal oxide nanostructures,such as nanoplates,nanowalls,and nanosheets,have received further attentions in recent years,due to their outstanding properties resulted from the small thickness and quantum size effects.In this work,lanthanum oxide nanosheets with the thickness of 56 nm had been successfully prepared by an originally simple method of carbon dioxide carbonation;the preparation process was green without using surfactants and detergent.The X-ray diffraction,transmission electron microscopy,and scanning electron microscopy were used to characterize the products.Thermogravimetric-differential thermal analysis and FT-IR were introduced to prove that the lanthanum oxide precursor with lamellar morphology was La2(CO3)3 3H2O.The carbon dioxide carbonation method would provide significant benefits containing mild reaction conditions,high efficiency,low cost,and easy to realize large-scale production.展开更多
This paper investigated the recovery of rare earth elements(REEs) and aluminum(AI) from the waste slag discharged by FCC catalyst factory(FCC waste slag) via acid leaching and selective precipitation.Analysis methods ...This paper investigated the recovery of rare earth elements(REEs) and aluminum(AI) from the waste slag discharged by FCC catalyst factory(FCC waste slag) via acid leaching and selective precipitation.Analysis methods such as ICP-AES, XRF and XRD were applied to obtain experiment data. The maximum leaching efficiency of REEs and Al was achieved at pH value of 1 and with liquid to solid ratio of 4:1,Under such conditions, 91.01%, 92.24% and 94.77% of La, Ce and Al were extracted at 20 ℃ for 2 h from the FCC waste slag, respectively. The SiOcontent in the leaching residue was 88.3%, which can be used as an available silicon resource. The REEs can be precipitated in the form of REEs and sodium double sulfate(NaRE(SO)·xHO) by adding NaSOto the leaching solution, while Al remained in the solution. Afterwards, the pH value of the filtrate was adjusted to 4.5, and Al was precipitated as AI(OH). Finally,NaRE(SO)·xHO and Al(OH)were converted into RECland Al(SO4)solution,respectively, which were recycled to manufacture zeolite. This process recovered REEs and Al from the FCC waste slag and reduced the emissions of waste slag simultaneously, which has an important economic and environment significance.展开更多
Based on the new process named "Combination Method" for metallurgy and separation of Baotou mixed rare earth concentrate(BMREC),the aim of this paper is to clearly elucidate the phase change behavior of BMRE...Based on the new process named "Combination Method" for metallurgy and separation of Baotou mixed rare earth concentrate(BMREC),the aim of this paper is to clearly elucidate the phase change behavior of BMREC without additives during oxidative roasting at 450-800℃.The results indicate that the bastnaesite in BMREC is decomposed at 450-550℃,the weight loss is about 10.3 wt%,and the activation energy(E) is 144 kJ/mol.The bastnaesite in BMREC is decomposed into rare earth fluoride,rare earth oxides(La_(2)O_(3),Ce_(7)O_(12),Pr_(6)O_(11) and Nd_(2)O_(3)),and CO_(2),particularly,with the increase of roasting temperature,bastnaesite in BMREC is more completely decomposed into LaF_(3),which causes a decrease in leaching rate of La during the HCI leaching process.Additionally,the maximum cerium oxidation efficiency reaches about 60 wt% when the roasting temperature is equal to or above 500℃,and the oxidation reaction rate of cerium increases with the increasing roasting temperature.展开更多
Magnesium bicarbonate solution is considered as an environmentally friendly extractant saponification agent for the solvent extraction of rare earth elements due to its advantage of minimum water pollution.In order to...Magnesium bicarbonate solution is considered as an environmentally friendly extractant saponification agent for the solvent extraction of rare earth elements due to its advantage of minimum water pollution.In order to reveal the extraction regularity, optimize production-process and guide the use of this new extraction system, the extraction of Nd(Ⅲ) in chloride medium with HEH/EHP saponified by magnesium bicarbonate solution was investigated with the self-designed constant interfacial area cell. Besides, the effects of stirring rate, temperature, specific interfacial area and concentration of Mg-HEH/EHP on the extraction rate of Nd(Ⅲ) were systematically investigated. Results show that, the rate of extraction is governed by both diffusion and chemical reaction, and the extraction reaction takes place at the interface. The apparent activation energy of the extraction reaction is 16.88 kJ/mol. The corresponding rate equation is deduced. The mechanisms and rate-determining step are speculated based on interfacial reaction models, which is consistent with the experimental results.展开更多
Phosphate rock has been considered as one of the potential promising resources for rare earth elements(REEs). But the cost issues and the technical challenges caused by the low content of REEs in ores did hinder the f...Phosphate rock has been considered as one of the potential promising resources for rare earth elements(REEs). But the cost issues and the technical challenges caused by the low content of REEs in ores did hinder the further development of REEs recovery technologies. In order to explore a green process for the recovery of REEs from phosphate rock, this study investigates the effects of phosphoric acid concentration, liquid-to-solid ratio(L/S ratio), leaching time and temperature on the leaching efficiencies of the major components from phosphate rock. A REEs recovery of 94.3% and a phosphorus recovery of 95.3%are achieved under the optimal conditions of attacking phosphate rock using 30%P_2 O_5 acid with an L/S ratio of 10:1 and a stirring speed of 250 r/min at 25 ℃ for 4 h. Then,the selective precipitation of REEs with 81.3% REEs recovery is realized by heating up the leaching solution from 25 to 90 ℃ and keeping for4 h. Thereafter, more than 95% phosphoric acid is recovered by H_2 SO_4 and high purity gypsum, more than95% CaSO_4(tested by XRF), is also produced at the same time. Ultimately, a green process that leaches phosphate rock with H_3 PO_4, selectively precipitates REEs from leaching solution by heating up, recovers H_3 PO_4 with H2 SO4 is proposed. Compared with REE recovery in traditional processes, this process owns the merits of simple operation, energy saving and minimum wastes.展开更多
As the oxygen redox ability shows great effects on the catalytic performances of ceria-zirconia based materials,many strategies have been utilized to improve the oxygen storage capacity.Here in this study,we report a ...As the oxygen redox ability shows great effects on the catalytic performances of ceria-zirconia based materials,many strategies have been utilized to improve the oxygen storage capacity.Here in this study,we report a simple and facile approach to prepare a SO_(4)^(2-)-modified La,Y-doped ceria-zirconia material(SO/CZLY-f)with high oxygen storage capacity.Due to the additional redox process between SO_(4)^(2-)and S^(2-),oxygen storage capacity of SO/CZLY-f(745.3μmol O_(2)/g)is about 1.6 times higher than that of La,Ydoped ceria-zirconia material without SO_(4)^(2-)modification.Moreover,the catalytic activities and stability of the corresponding Pd-only three-way catalyst were measured.Compared to that of Pd@CZLY-f,the operation window of CO,full conversion temperature of HC and NO over Pd@SO/CZLY-f are obviously widened and lowered,respectively.After aging treatment at 1100℃for 4 h,the superiority of aged Pdloading composite is still maintained.展开更多
In order to clarify the solvent extraction and separation behaviors of rare earths and impurity of Al during the extraction and enrichment of low-concentration leach solution of ion-adsorption rare earth ore,the extra...In order to clarify the solvent extraction and separation behaviors of rare earths and impurity of Al during the extraction and enrichment of low-concentration leach solution of ion-adsorption rare earth ore,the extraction mechanism and separation behaviors of Nd^(3+)and Al^(3+)in the Nd_(2)(SO_(4))_(3)-AI_(2)(SO_(4))_(3) mixed solution using P507 were studied in this work.The extraction of Nd^(3+)and Al^(3+)follows the cation exchange mechanism.With the increase of the equilibrium pH,β_(Nd/Al) in the extraction of the Nd_(2)(SO_(4))_(3)-Al_(2)(SO_(4))_(3) mixed solution using P507 is always higher than that in the extraction of single Nd_(2)(SO_(4))_(3) and Al_(2)(SO_(4))_(3) solutions.It can be attributed to the fact that the extraction of Nd^(3+)using P507 is much faster than that of Al^(3+),and Al^(3+)is more prone to be hydrolyzed at lower pH.β_(Nd/Al) in the extraction of the Nd_(2)(SO_(4))_(3)-Al_(2)(SO_(4))_(3) mixed solution decreases gradually with the increase of mixing time within the equilibrium pH range of 1.5-1.9.The extraction of Nd^(3+)using P507 is much faster than that of Al^(3+),but the stability of Al^(3+)-Ioaded organic phase is better than that of Nd^(3+)-loaded organic phase,thus Nd^(3+)in the Nd^(3+)-loaded organic phase is gradually replaced by Al^(3+)in the aqueous phase with the increase of mixing time.展开更多
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 wastewat...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.展开更多
Ceria-zirconia mixed oxides(CZMO)are widely used in many important catalysis fields.However,pure CZMO is known to have poor thermal stability.In this paper,a strategy was proposed to design Ce_(0.475)Zr_(0.475)M_(0.05...Ceria-zirconia mixed oxides(CZMO)are widely used in many important catalysis fields.However,pure CZMO is known to have poor thermal stability.In this paper,a strategy was proposed to design Ce_(0.475)Zr_(0.475)M_(0.05)O_(2)(M=La,Y,Pr,Nd,Pm,Sm,Eu,Gd,Tb,Er,Lu,and,Yb)oxide surface with high thermal stability by using first-principles molecular dynamics(FPMD)simulation and experiment method.Through the structure stability analysis at different temperatures,the surface energyγas a function of R_(ion)/D_(ave)is identified as a quantitative structure descriptor for analyzing the doping effect of rare earth(RE)elements on the thermal stability of Ce_(0.475)Zr_(0.475)M_(0.05)O_(2).By doping the suitable RE,γcan be adjusted to the optimal range to enhance the thermal stability of Ce_(0.475)Zr_(0.475)M_(0.05)O_(2).With this strategy,it can be predicted that the sequence of thermal stability improvement is Y>La>Gd>Nd>Pr>Pm>Sm>Eu>Tb>Er>Yb>Lu,which was further verified by our experiment results.After thermal treatment at 1100℃for 10 h,the specific surface area(SSA)of aged Y-CZ and La-CZ samples can reach 21.34 and 19.51 m~2/g,which is 63.02%and 49.04%higher than the CZMO sample without doping because the surface doping of Y and La is in favor of inhibiting the surface atoms thermal displacement.In a word,the strategy proposed in this work can be expected to provide a viable way for designing the highly efficient CZMO materials in extensive applications and promoting the usages of the high-abundance rare-earth elements Y and La.展开更多
Numerous light rare earth elements(LREE)minerals containing Fe and P were processed by sulfuric acid roasting method,and the leaching solution mainly comprises LREE sulfate,Fe2(SO4)3,H3PO4,and H2SO4,however,the solubi...Numerous light rare earth elements(LREE)minerals containing Fe and P were processed by sulfuric acid roasting method,and the leaching solution mainly comprises LREE sulfate,Fe2(SO4)3,H3PO4,and H2SO4,however,the solubility data of LREE sulfates in this system is few.This work studies the solubility of LREE sulfates in independent LREE sulfate system RE2(SO4)3-Fe2(SO4)3-H3 PO4-H2SO4(RE=La,Ce,Pr or Nd)and mixed LREE sulfates system(La,Ce,Pr,Nd)2(SO4)3-Fe2(SO4)3-H3 PO4-H2SO4 at different temperature(25-65℃)and concentrations of Fe2(SO4)3(Fe2 O3,0-50.13 g/L),H2SO4(0.5 mol/L),and H3 PO4(P2 O5,20.34 g/L)based on the industrial operating condition at low liquid and solid ratio 2:1.The solubility of each LREE sulfate in the independent system(La2 O3,12.25-20.88 g/L;CeO2,41.93-62.35 g/L;Pr6 O11,37.34-56.69 g/L;Nd2 O3,26.60-37.63 g/L)is much higher than that of the mixed system(La2 O3,6.95-11.03 g/L;CeO2,10.63-21.51 g/L;Pr6 O11,11.56-20.36 g/L;Nd2 O3,12.36-19.79 g/L)under the same other conditions.The results also indicate that,in the two systems,both Fe and the temperature have negative effects on the solubility of LREE sulfates.That may occur due to the complication reactions between the complexes of RESO4+and Fe(SO4)2-.However,the influence degree of temperature and iron concentration on the LREE sulfates solubility varies in the two systems and among different LREE species.This research is of theoretical significance for optimizing the conditions of the sulfuric acid process for recovering the LREE from the mixed LREE bearing minerals as well as the single LREE containing secondary rare earth scraps.展开更多
In order to achieve deeper understanding of rare earth elements(REEs) behaviors during phosphate rock processing with H_3PO_4. The solubility of REEs in Ca(H_2PO_4)_2-H_3PO_4 solutions with various concentrations of C...In order to achieve deeper understanding of rare earth elements(REEs) behaviors during phosphate rock processing with H_3PO_4. The solubility of REEs in Ca(H_2PO_4)_2-H_3PO_4 solutions with various concentrations of Ca(H_2PO_4)_2 at different temperatures were tested. The results demonstrate that REEs solubility decreases sharply with the increasing concentration of Ca(H_2PO_4)_2. Equations between [REE^(3+)] and [H^+],[H^+] and [Ca^(2+)] in Ca(H_2PO_4)_2-H_3PO_4 solutions were built based on the precipitation-dissolution equilibrium of rare earth phosphates and the ionization equilibrium of H_3PO_4. According to the equations, the decreasing mechanism of REEs solubility caused by elevated concentration of Ca(H_2PO_4)_2 was determined. The mechanism can be illustrated as that the elevated concentration of [H_2 PO_4^-] decreases the concentration of hydrogen ion by retarding the ionization process of H_3PO_4 and directly promotes the precipitation of rare earth phosphates. Furthermore, it can be easy deduced that similar effect would be caused by the other cation impurities(Fe^(3+), Al^(3+), etc.) on REEs solubility based on the mechanism. In addition, superimposed reduction effect on REEs solubility caused by the elevated concentration of Ca(H_2PO_4)_2 and the elevated temperature is found. This superimposed effect leads to a super low solubility of REEs in Ca(H_2PO_4)_2-H_3PO_4 solution. On the basis of the experimental study, outlooks and suggestions for further development of REEs recovery method are given.展开更多
In order to improve the application values of Ce element, in this paper, rare earth chloride solution was used as raw material, the pH value was controlled by inorganic alkali, the ceria powders with special physical ...In order to improve the application values of Ce element, in this paper, rare earth chloride solution was used as raw material, the pH value was controlled by inorganic alkali, the ceria powders with special physical properties were prepared by carbon dioxide carbonization method. According to characterization of SEM, XRD, and TG-DSC, Ce（OH）3 prepared at pH = 7.5 exhibits smaller particle size than that prepared at other conditions. CeO2 precursor obtained by direct carbonization of Ce（OH）3 shows smaller particle size and narrow size distribution, CeO2 precursor forms at first by carbonization of Ce（OH）3 with the continuous addition of CO2 gas,and the chemical component is indicated to be Ce2 O（CO3）2·6 H2 O.Cubic phase CeO2 powders are obtained by calcined at 750 ℃ for 4 h. The mean particle size D（50） is0.941 μm, and particle size distribution is smaller than 1. The microscopic appearance is homogeneous,with a spherical-like shape and a grain size of 200-500 nm. The light quality characteristics of sedimentation volume and accumulation density are obviously better than those of carbonate precipitation products. The carbonization method can be used not only to obtain ultra-fine rare earth oxides with fine particle size, narrow distribution and high dispersion properties, but also to achieve the reuse of carbon dioxide greenhouse gas.展开更多
To monitor the reaction between Ce^(4+) ion and Cl-ion at the electron level,an electrochemical experiment was designed in this work.Herein,the intermediate and final products that may be produced during the redox rea...To monitor the reaction between Ce^(4+) ion and Cl-ion at the electron level,an electrochemical experiment was designed in this work.Herein,the intermediate and final products that may be produced during the redox reaction are directly tracked by using cyclic voltammetry,and the influences of Ce^(4+) ion concentration,temperatu re and F-ion on the reduction peak potential of Ce^(4+) ion were investigated.The results show that Ce^(4+) ion reacts with Cl-ion through an irreversible reaction without any intermediate products,and the rate-determining step of the reaction is diffusion during the electrode reaction.The effects of temperature(20-40℃) and Ce^(4+) ion concentration(0.04-0.12 mol/L) on the reduction peak pote ntial of Ce^(4+) ion can be ignored,but the higher the molar ratio of F-to Ce^(4+)(0-3 mol/mol),the mo re easily the reduction of Ce^(4+) ion to Ce^(3+) ion occurs.Additionally,the Ce^(4+) ions are preferentially reduced by thiourea when thiourea is added in the HCl solution,and thiourea inhibits the oxidation of Cl-ions to Cl_(2) by forming a complex with Cl-ions.This work provides a theoretical basis for the role of thiourea in inhibiting Cl_(2) production and offers a new way to find new reductants.展开更多
基金Project supported by the National Key Research and Development Program of China(2020YFC1909002)the Major Research Plan of the National Natural Science Foundation of China(91962211)the Science and Technology Innovation Fund of GRINM(2022PD0102)。
文摘Weathered crust elution-deposited rare earth ore is crucial source of medium and heavy rare earths,with in-situ leaching being the most common mining method.The high contents of impurity of aluminum in the leach solution are a significant challenge for the subsequent enrichment process of rare earths.A comprehensive understanding of the occurrences and vertical distribution of aluminum and rare earths within typical vertical profiles can provide valuable insights into entire design of the in-situ leaching.This paper improves a five-step sequential extraction method to analyze the occurrence and vertical distribution of rare earths and aluminum in vertical profiles from Chongzuo and Longyan.Experimental results demonstrate that soil solution pH is the main factor affecting the vertical distribution of ionexchangeable rare earths.Both samples have distinct areas of enrichment for ion-exchangeable rare earths or aluminum.Ion-exchangeable rare earths are primary concentrated in the middle and lower parts of the ore layer(4-13 m in Chongzuo,14-22 m in Longyan),while the ion-exchangeable aluminum is mainly enriched in the upper part of the ore layer(1-5 m in Chongzuo,and 2-14 m in Longyan).The vertical distribution of inorganic hydroxy aluminum is likely influenced by the micromorphology and particle size of the clay minerals.The inorganic hydroxy aluminum concentration in Chongzuo samples decreases continuously from 415.65 to 120.95 mg/kg with increasing sampling depth,whereas the concentration in Longyan samples(110.55-171.27 mg/kg)is almost independence with sampling depth.These results provide direct guidance for the entire design of the injection well depth and the leaching parameters,thereby inhibiting the leaching of impurity of aluminum and lower the consumption of leaching agent.
基金Project supported by the National Key Research and Development Program of China(2020YFC1909104)。
文摘To find a greener and more economical approach for treating the Mountain Pass rare earth concentrate(MPREC),a novel "Combination Method",including the processes of oxidizing roasting,HCI leaching and sulfuric acid roasting,is proposed in this research.In this paper,the effect of phase transition behavior in hydrochloric acid leaching during oxidative roasting at 450-600℃ was studied.During roasting,the bastnasite in MPREC is decomposed into CeLa_(2)O_(3)F_(3) and(Ce_(0.33),La_(0.33),Ca_(0.33))O_(1.5).As the CeLa_(2)O_(3)F_(3) phase has the fluorine-fixation effect,the generated CeLa_(2)O_(3)F_(3) phase can not be dissolved by HCI after roasting at 500 and 550℃,but it can be decomposed by HCI after roasting at over 600℃,resulting in the improvement of the leaching rate of total F element.The maximum leaching efficiency of rare earth elements(REEs) can reach 70.32 wt% at the roasting temperature of 550℃.After roasting at over 600℃,some F^-ions in the solution combined with RE^(3+) to form REF_(3) precipitate and enter the leaching residue,and the others are in the form of [CeF_(3)]^+ in the leaching solution during leaching,therefore,the leaching efficiency of non-ce rium REEs decreases while that of cerium element increases.This work provides basic research for optimizing the actual production process of MPREC.
基金supported by the National Key Research and Development Program of China(No.2022YFB3504202)the National Natural Science Foundation of China(No.52204376)Youth Foundation of Hebei Province(No.E2022103007).
文摘With the continuous tightening of automotive emission regulations and the increasing promotion of energy-efficient hybrid vehicles,new challenges have arisen for the low-temperature performance of three-way catalysts(TWCs).To guide the design of next-generation TWCs,it is essential to further develop our understanding of the relationships between microstructure and catalytic performance.Here,Rh/CeO_(2)–ZrO_(2) catalysts were synthesized with different Rh metal dispersion by using a combination of the wet impregnation method and reduction treatment.These catalysts included Rh single-atom catalysts,cluster catalysts,and nanoparticle catalysts.The results showed that the Rh nanoparticle catalyst,with an average size of 1.9 nm,exhibited superior three-way catalytic performance compared to the other catalysts.Based on the catalytic activity in a series of simple reaction atmospheres such as CO+O_(2),NO+CO,and hydrocarbons(HCs)+O_(2) and operando infrared spectroscopy,we found that metallic Rh sites on Rh nanoparticles are the key factor responsible for the low-temperature catalytic performance.
基金supported by the National Science and Technology Support Program of China(2015BAB16B02)the National Natural Science Foundation of China(51504034).
文摘In acid treatment technology of Baotou mixed rare earth ore,large quantities of ammonia-nitrogen wastewater are produced in the step of ammonium bicarbonate precipitation to transform rare earth sulfate.In this paper,we adopted a green precipitant magnesium bicarbonate(Mg(HCO3)2) to substitute ammonium bicarbonate to eliminate ammonia-nitrogen pollution.The effects of n(HCO3^-):n(RE^3+),aging temperature and aging time on the crystallization using Mg(HCO3)2 precipitation method were investigated.The results indicate that the rare earths could be completely recovered when n(HCO3^-):n(RE^3+) is higher than 3.15:1.The crystal water content of rare earth carbonates is affected by the aging temperature.The precipitate has a bad filterability when the aging temperature is over 40℃.This can be attributed to the less crystallized water molecules of the hydrated rare earth carbonate precipitation.The mixed rare earth carbonates are prone to be crystalline,and have a good filterability at aging temperatures below 40℃.Meanwhile,the evolution mechanism of crystalline mixed rare earth carbonates is reasonably deduced,the amorphous rare earth carbonates are first dissolute and then recrystallized.Under the optimized aging conditions,the purity of the crystalline precipitate meets the requirements of the fine product standard(GB/T 16479-2008).The filtrated could be used to produce Mg(HCO3)2,thus to realize the recycling of magnesium sulfate.
基金supported by National Science and Technology Support Program of China(2015BAB16B03)the National Natural Science Foundation of China(51504034,51674037)
文摘Rare earths(REs) are of vital importance for the development of new materials and green energy.Magnesium bicarbonate is one of the most recyclable and environmental-friendly precipitant for REs recovery from leaching solutions. Nd_2(CO_3)_3 has difficulties in industrial production. So in this study,the precipitation of neodymium from chloride solution by magnesium bicarbonate are investigated. The effects of feeding method, [HCO_3^-]/[Nd^(3+)] mole ratio, feeding speed and reaction temperature on yield and impurity(magnesia) content are systematically studied. Results show that the impurity(magnesia)content decreases to 0.010 wt% with a yield approaching to 100% obtained under the conditions of[HCO_3^-]/[Nd^(3+)] = 3.00 by parallel flow addition at 50 ℃. The major impurity(magnesia) in rare earth carbonates mainly presents in the form of physical absorption, which can be easily removed by scrubbing. Therefore, it offers a promising green process that uses magnesium bicarbonate to produce neodymium carbonate due to its cycling of carbon dioxide, magnesium salt and waste water.
基金Project supported by National Natural Science Foundation of China(51504034)Beijing Nova Program(Z181100006218030)
文摘Solid oxide fuel cell is a promising energy conversion system which converts chemical energy into electrical energy directly. Electrolyte is the key component and determines the working temperature. In this paper,ceria and scandia co-doped zirconia electrolytes sintered from 1300 to 1550 ℃ were chosen as research objects. Scanning electron microscopy, X-ray diffraction and transmission electron microscopy were performed to characterize the ceramic samples. The effects of grain size and grain boundary element segregation on the electrical conductivity were focused. Electrochemical impedance spectroscopy was used to calculate the bulk, grain boundary and specific grain boundary conductivity. Results show that the bulk and grain boundary ionic conductivity increases with the increasing grain size.However, the specific grain boundary conductivity decreases with the increasing grain size. This is explained by the fact that Sc^(3+) is segregated at the grain boundary, which leads to higher oxygen vacancy concentration when sintered at lower temperature.
基金supported by the National Natural Science Foundation of China (50934004)the National High Technology Research & Development Program of China (2010AA03A405)National Science and Technology Support Program of China (2012BAE01B02)
文摘Two-dimensional metal oxide nanostructures,such as nanoplates,nanowalls,and nanosheets,have received further attentions in recent years,due to their outstanding properties resulted from the small thickness and quantum size effects.In this work,lanthanum oxide nanosheets with the thickness of 56 nm had been successfully prepared by an originally simple method of carbon dioxide carbonation;the preparation process was green without using surfactants and detergent.The X-ray diffraction,transmission electron microscopy,and scanning electron microscopy were used to characterize the products.Thermogravimetric-differential thermal analysis and FT-IR were introduced to prove that the lanthanum oxide precursor with lamellar morphology was La2(CO3)3 3H2O.The carbon dioxide carbonation method would provide significant benefits containing mild reaction conditions,high efficiency,low cost,and easy to realize large-scale production.
基金Project supported by the Rare-earth Adjustment Upgrade Projects of Ministry of Industry and Information Technology of ChinaBeijing Nova Program(Z161100004916108)
文摘This paper investigated the recovery of rare earth elements(REEs) and aluminum(AI) from the waste slag discharged by FCC catalyst factory(FCC waste slag) via acid leaching and selective precipitation.Analysis methods such as ICP-AES, XRF and XRD were applied to obtain experiment data. The maximum leaching efficiency of REEs and Al was achieved at pH value of 1 and with liquid to solid ratio of 4:1,Under such conditions, 91.01%, 92.24% and 94.77% of La, Ce and Al were extracted at 20 ℃ for 2 h from the FCC waste slag, respectively. The SiOcontent in the leaching residue was 88.3%, which can be used as an available silicon resource. The REEs can be precipitated in the form of REEs and sodium double sulfate(NaRE(SO)·xHO) by adding NaSOto the leaching solution, while Al remained in the solution. Afterwards, the pH value of the filtrate was adjusted to 4.5, and Al was precipitated as AI(OH). Finally,NaRE(SO)·xHO and Al(OH)were converted into RECland Al(SO4)solution,respectively, which were recycled to manufacture zeolite. This process recovered REEs and Al from the FCC waste slag and reduced the emissions of waste slag simultaneously, which has an important economic and environment significance.
基金Project supported by the National Key Research and Development Program of China(2020YFC1909104)Science and Technology Major Project of Guangxi(GuikeAA18242022)Hebei Province Key Research and Development Plan Project(20374104D)。
文摘Based on the new process named "Combination Method" for metallurgy and separation of Baotou mixed rare earth concentrate(BMREC),the aim of this paper is to clearly elucidate the phase change behavior of BMREC without additives during oxidative roasting at 450-800℃.The results indicate that the bastnaesite in BMREC is decomposed at 450-550℃,the weight loss is about 10.3 wt%,and the activation energy(E) is 144 kJ/mol.The bastnaesite in BMREC is decomposed into rare earth fluoride,rare earth oxides(La_(2)O_(3),Ce_(7)O_(12),Pr_(6)O_(11) and Nd_(2)O_(3)),and CO_(2),particularly,with the increase of roasting temperature,bastnaesite in BMREC is more completely decomposed into LaF_(3),which causes a decrease in leaching rate of La during the HCI leaching process.Additionally,the maximum cerium oxidation efficiency reaches about 60 wt% when the roasting temperature is equal to or above 500℃,and the oxidation reaction rate of cerium increases with the increasing roasting temperature.
基金Project supported by National Science and Technology Support Program of China(2015BAB16B03,2015BAB16B02)National Natural Science Foundation of China(51674037,51504034)
文摘Magnesium bicarbonate solution is considered as an environmentally friendly extractant saponification agent for the solvent extraction of rare earth elements due to its advantage of minimum water pollution.In order to reveal the extraction regularity, optimize production-process and guide the use of this new extraction system, the extraction of Nd(Ⅲ) in chloride medium with HEH/EHP saponified by magnesium bicarbonate solution was investigated with the self-designed constant interfacial area cell. Besides, the effects of stirring rate, temperature, specific interfacial area and concentration of Mg-HEH/EHP on the extraction rate of Nd(Ⅲ) were systematically investigated. Results show that, the rate of extraction is governed by both diffusion and chemical reaction, and the extraction reaction takes place at the interface. The apparent activation energy of the extraction reaction is 16.88 kJ/mol. The corresponding rate equation is deduced. The mechanisms and rate-determining step are speculated based on interfacial reaction models, which is consistent with the experimental results.
基金Project supported by the National Natural Science Foundation of China(51674036)the Beijing Nova Program(Z161100004916108)
文摘Phosphate rock has been considered as one of the potential promising resources for rare earth elements(REEs). But the cost issues and the technical challenges caused by the low content of REEs in ores did hinder the further development of REEs recovery technologies. In order to explore a green process for the recovery of REEs from phosphate rock, this study investigates the effects of phosphoric acid concentration, liquid-to-solid ratio(L/S ratio), leaching time and temperature on the leaching efficiencies of the major components from phosphate rock. A REEs recovery of 94.3% and a phosphorus recovery of 95.3%are achieved under the optimal conditions of attacking phosphate rock using 30%P_2 O_5 acid with an L/S ratio of 10:1 and a stirring speed of 250 r/min at 25 ℃ for 4 h. Then,the selective precipitation of REEs with 81.3% REEs recovery is realized by heating up the leaching solution from 25 to 90 ℃ and keeping for4 h. Thereafter, more than 95% phosphoric acid is recovered by H_2 SO_4 and high purity gypsum, more than95% CaSO_4(tested by XRF), is also produced at the same time. Ultimately, a green process that leaches phosphate rock with H_3 PO_4, selectively precipitates REEs from leaching solution by heating up, recovers H_3 PO_4 with H2 SO4 is proposed. Compared with REE recovery in traditional processes, this process owns the merits of simple operation, energy saving and minimum wastes.
基金Project supported by the Beijing Nova Program(Z181100006218030)Major State Research Development Program of Hebei province(20374202D)。
文摘As the oxygen redox ability shows great effects on the catalytic performances of ceria-zirconia based materials,many strategies have been utilized to improve the oxygen storage capacity.Here in this study,we report a simple and facile approach to prepare a SO_(4)^(2-)-modified La,Y-doped ceria-zirconia material(SO/CZLY-f)with high oxygen storage capacity.Due to the additional redox process between SO_(4)^(2-)and S^(2-),oxygen storage capacity of SO/CZLY-f(745.3μmol O_(2)/g)is about 1.6 times higher than that of La,Ydoped ceria-zirconia material without SO_(4)^(2-)modification.Moreover,the catalytic activities and stability of the corresponding Pd-only three-way catalyst were measured.Compared to that of Pd@CZLY-f,the operation window of CO,full conversion temperature of HC and NO over Pd@SO/CZLY-f are obviously widened and lowered,respectively.After aging treatment at 1100℃for 4 h,the superiority of aged Pdloading composite is still maintained.
基金Project supported by the Major Research Plan of the National Natural Science Foundation of China(91962211)National Key Research and Development Program of China(2018YFC1801803)+1 种基金National Natural Science Foundation of China(51804273)Major Project of Guangxi Science and Technology(Guike-AA18242022)。
文摘In order to clarify the solvent extraction and separation behaviors of rare earths and impurity of Al during the extraction and enrichment of low-concentration leach solution of ion-adsorption rare earth ore,the extraction mechanism and separation behaviors of Nd^(3+)and Al^(3+)in the Nd_(2)(SO_(4))_(3)-AI_(2)(SO_(4))_(3) mixed solution using P507 were studied in this work.The extraction of Nd^(3+)and Al^(3+)follows the cation exchange mechanism.With the increase of the equilibrium pH,β_(Nd/Al) in the extraction of the Nd_(2)(SO_(4))_(3)-Al_(2)(SO_(4))_(3) mixed solution using P507 is always higher than that in the extraction of single Nd_(2)(SO_(4))_(3) and Al_(2)(SO_(4))_(3) solutions.It can be attributed to the fact that the extraction of Nd^(3+)using P507 is much faster than that of Al^(3+),and Al^(3+)is more prone to be hydrolyzed at lower pH.β_(Nd/Al) in the extraction of the Nd_(2)(SO_(4))_(3)-Al_(2)(SO_(4))_(3) mixed solution decreases gradually with the increase of mixing time within the equilibrium pH range of 1.5-1.9.The extraction of Nd^(3+)using P507 is much faster than that of Al^(3+),but the stability of Al^(3+)-Ioaded organic phase is better than that of Nd^(3+)-loaded organic phase,thus Nd^(3+)in the Nd^(3+)-loaded organic phase is gradually replaced by Al^(3+)in the aqueous phase with the increase of mixing time.
基金Project supported by the National Natural Science Foundation of China(51674037,51674036)Guangxi Science and Technology Major Project(Guike-AA18242022)。
文摘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.
基金Project supported by China Postdoctoral Science Foundation(2020M680616)Major State Research Development Program of Hebei province(20374202D)。
文摘Ceria-zirconia mixed oxides(CZMO)are widely used in many important catalysis fields.However,pure CZMO is known to have poor thermal stability.In this paper,a strategy was proposed to design Ce_(0.475)Zr_(0.475)M_(0.05)O_(2)(M=La,Y,Pr,Nd,Pm,Sm,Eu,Gd,Tb,Er,Lu,and,Yb)oxide surface with high thermal stability by using first-principles molecular dynamics(FPMD)simulation and experiment method.Through the structure stability analysis at different temperatures,the surface energyγas a function of R_(ion)/D_(ave)is identified as a quantitative structure descriptor for analyzing the doping effect of rare earth(RE)elements on the thermal stability of Ce_(0.475)Zr_(0.475)M_(0.05)O_(2).By doping the suitable RE,γcan be adjusted to the optimal range to enhance the thermal stability of Ce_(0.475)Zr_(0.475)M_(0.05)O_(2).With this strategy,it can be predicted that the sequence of thermal stability improvement is Y>La>Gd>Nd>Pr>Pm>Sm>Eu>Tb>Er>Yb>Lu,which was further verified by our experiment results.After thermal treatment at 1100℃for 10 h,the specific surface area(SSA)of aged Y-CZ and La-CZ samples can reach 21.34 and 19.51 m~2/g,which is 63.02%and 49.04%higher than the CZMO sample without doping because the surface doping of Y and La is in favor of inhibiting the surface atoms thermal displacement.In a word,the strategy proposed in this work can be expected to provide a viable way for designing the highly efficient CZMO materials in extensive applications and promoting the usages of the high-abundance rare-earth elements Y and La.
基金Project supported by the National Natural Science Foundation of China(51674037)GRINM Youth Foundation。
文摘Numerous light rare earth elements(LREE)minerals containing Fe and P were processed by sulfuric acid roasting method,and the leaching solution mainly comprises LREE sulfate,Fe2(SO4)3,H3PO4,and H2SO4,however,the solubility data of LREE sulfates in this system is few.This work studies the solubility of LREE sulfates in independent LREE sulfate system RE2(SO4)3-Fe2(SO4)3-H3 PO4-H2SO4(RE=La,Ce,Pr or Nd)and mixed LREE sulfates system(La,Ce,Pr,Nd)2(SO4)3-Fe2(SO4)3-H3 PO4-H2SO4 at different temperature(25-65℃)and concentrations of Fe2(SO4)3(Fe2 O3,0-50.13 g/L),H2SO4(0.5 mol/L),and H3 PO4(P2 O5,20.34 g/L)based on the industrial operating condition at low liquid and solid ratio 2:1.The solubility of each LREE sulfate in the independent system(La2 O3,12.25-20.88 g/L;CeO2,41.93-62.35 g/L;Pr6 O11,37.34-56.69 g/L;Nd2 O3,26.60-37.63 g/L)is much higher than that of the mixed system(La2 O3,6.95-11.03 g/L;CeO2,10.63-21.51 g/L;Pr6 O11,11.56-20.36 g/L;Nd2 O3,12.36-19.79 g/L)under the same other conditions.The results also indicate that,in the two systems,both Fe and the temperature have negative effects on the solubility of LREE sulfates.That may occur due to the complication reactions between the complexes of RESO4+and Fe(SO4)2-.However,the influence degree of temperature and iron concentration on the LREE sulfates solubility varies in the two systems and among different LREE species.This research is of theoretical significance for optimizing the conditions of the sulfuric acid process for recovering the LREE from the mixed LREE bearing minerals as well as the single LREE containing secondary rare earth scraps.
基金Project supported by National Natural Science Foundation of China(51674036)Beijing Nova Program(Z161100004916108)
文摘In order to achieve deeper understanding of rare earth elements(REEs) behaviors during phosphate rock processing with H_3PO_4. The solubility of REEs in Ca(H_2PO_4)_2-H_3PO_4 solutions with various concentrations of Ca(H_2PO_4)_2 at different temperatures were tested. The results demonstrate that REEs solubility decreases sharply with the increasing concentration of Ca(H_2PO_4)_2. Equations between [REE^(3+)] and [H^+],[H^+] and [Ca^(2+)] in Ca(H_2PO_4)_2-H_3PO_4 solutions were built based on the precipitation-dissolution equilibrium of rare earth phosphates and the ionization equilibrium of H_3PO_4. According to the equations, the decreasing mechanism of REEs solubility caused by elevated concentration of Ca(H_2PO_4)_2 was determined. The mechanism can be illustrated as that the elevated concentration of [H_2 PO_4^-] decreases the concentration of hydrogen ion by retarding the ionization process of H_3PO_4 and directly promotes the precipitation of rare earth phosphates. Furthermore, it can be easy deduced that similar effect would be caused by the other cation impurities(Fe^(3+), Al^(3+), etc.) on REEs solubility based on the mechanism. In addition, superimposed reduction effect on REEs solubility caused by the elevated concentration of Ca(H_2PO_4)_2 and the elevated temperature is found. This superimposed effect leads to a super low solubility of REEs in Ca(H_2PO_4)_2-H_3PO_4 solution. On the basis of the experimental study, outlooks and suggestions for further development of REEs recovery method are given.
基金Project supported by National Key Technology Research and Development Program of the Ministry of Science and Technology of China(2015BAB16B03)the National Nature Science Foundation of China(51504034,51674037)
文摘In order to improve the application values of Ce element, in this paper, rare earth chloride solution was used as raw material, the pH value was controlled by inorganic alkali, the ceria powders with special physical properties were prepared by carbon dioxide carbonization method. According to characterization of SEM, XRD, and TG-DSC, Ce（OH）3 prepared at pH = 7.5 exhibits smaller particle size than that prepared at other conditions. CeO2 precursor obtained by direct carbonization of Ce（OH）3 shows smaller particle size and narrow size distribution, CeO2 precursor forms at first by carbonization of Ce（OH）3 with the continuous addition of CO2 gas,and the chemical component is indicated to be Ce2 O（CO3）2·6 H2 O.Cubic phase CeO2 powders are obtained by calcined at 750 ℃ for 4 h. The mean particle size D（50） is0.941 μm, and particle size distribution is smaller than 1. The microscopic appearance is homogeneous,with a spherical-like shape and a grain size of 200-500 nm. The light quality characteristics of sedimentation volume and accumulation density are obviously better than those of carbonate precipitation products. The carbonization method can be used not only to obtain ultra-fine rare earth oxides with fine particle size, narrow distribution and high dispersion properties, but also to achieve the reuse of carbon dioxide greenhouse gas.
基金Project supported by the National Key Research and Development Program of China (2020YFC1909104)Science and Technology Major Project of Guangxi (Guike AA18242022)+1 种基金Hebei Province Key Research and Development Plan Project (20374104D)。
文摘To monitor the reaction between Ce^(4+) ion and Cl-ion at the electron level,an electrochemical experiment was designed in this work.Herein,the intermediate and final products that may be produced during the redox reaction are directly tracked by using cyclic voltammetry,and the influences of Ce^(4+) ion concentration,temperatu re and F-ion on the reduction peak potential of Ce^(4+) ion were investigated.The results show that Ce^(4+) ion reacts with Cl-ion through an irreversible reaction without any intermediate products,and the rate-determining step of the reaction is diffusion during the electrode reaction.The effects of temperature(20-40℃) and Ce^(4+) ion concentration(0.04-0.12 mol/L) on the reduction peak pote ntial of Ce^(4+) ion can be ignored,but the higher the molar ratio of F-to Ce^(4+)(0-3 mol/mol),the mo re easily the reduction of Ce^(4+) ion to Ce^(3+) ion occurs.Additionally,the Ce^(4+) ions are preferentially reduced by thiourea when thiourea is added in the HCl solution,and thiourea inhibits the oxidation of Cl-ions to Cl_(2) by forming a complex with Cl-ions.This work provides a theoretical basis for the role of thiourea in inhibiting Cl_(2) production and offers a new way to find new reductants.
