Extraction kinetics and kinetic separation of La(Ⅲ),Gd(Ⅲ),Ho(Ⅲ) and Lu(Ⅲ) from chloride medium by HEHEHP

Acco rding to the tetrad-effect,14 elements of lanthanides can be divided into four groups.In our previous study,a new approach was proposed for the kinetic separation of four rare earth ions La(Ⅲ),Gd(Ⅲ),Ho(Ⅲ) and Lu(Ⅲ) coming from four groups.In that study,four rare-earth ions were kinetically separated from their coexisting mixed aqueous solutions,by performing liquid-column elution using the aqueous solution containing four lanthanide rare-earth ions as the stationary phase and the dispersed organic oil droplets containing HEHEHP(2-ethyl hexyl phosphonic acid mono 2-ethyl hexyl ester) extractant as the mobile phase.The study of extraction kinetics is very important for understanding the kinetic separation of rare earth ions,which was carried out in this paper.The extraction kinetics of La(Ⅲ),Gd(Ⅲ),Ho(Ⅲ) and Lu(Ⅲ) by HEHEHP diluted in heptane were investigated using single drop method.The different parameters affecting the extraction rate such as column length,specific interfacial area,rare earth ion concentration,extractant concentration,hydrogen ion concentration and temperature were separately studied and the rate equations are deduced.It is first order with respect to rare earth ion and HEHEHP concentrations,and negative first order with respect to hydrogen ion concentrations.The rate constants at 293.15 K are 10~(-6.23),10~(-5.73),10~(-5.58) and 10~(-5.43),respectively.The experimental results demonstrate that the extraction rate of La(Ⅲ), Gd(Ⅲ),Ho(Ⅲ) or Lu(Ⅲ) is diffusion-controlled,and the extraction reaction takes place at the interface rather than in the bulk phase.The extraction model was proposed.Besides,the kinetic separation of rare earth ions by HEHEHP oil drops was discussed.     

Solvent extraction and separation of light rare earth elements (La,Pr and Nd) in the presence of lactic acid as a complexing agent by Cyanex 272 in kerosene and the effect of citric acid,acetic acid and Titriplex Ⅲ as auxiliary agents

At present, the use of rare earth elements(REEs) has become an inevitable necessity in many modern industries. In general, liquid extraction is the best commercial method for extracting REEs due to its ability to control high volumes of liquids with electrical load. With the aim of improving a separation technology that would be superior to the existing extraction systems, the extraction behaviors of La(Ⅲ),Pr(Ⅲ), and Nd(Ⅲ) from an HCI medium with Cyanex 272 in the presence of the complexing agent lactic acid(HLac) and auxiliary agents citric acid(H_3 Cit), acetic acid(HAc), and Titriplex Ⅲ have been reported.The effect of pH and lactic acid concentration has been examined. The use of lactic acid as a complexing agent leading to a high extraction of REEs with Cyanex 272 at pH = 5 was compared with systems without lactic acid. The results show that the use of acetic acid along with lactic acid leads to an increase in the extraction percentage of LREEs. While use of citric acid and Titriplex Ⅲ reduces the extraction percentage of LREEs. Finally, the presence of Titriplex Ⅲ together with lactic acid could lead to an increase in the separation factor of Pr and Nd.     

A novel method for synthesis of styryl phosphonate monoester and its application in La(Ⅲ) extraction

Herein,styryl phosphonate monoester(SPE) was synthesized and first introduced as rare earth extractant.The solvent extraction of lanthanum(Ⅲ) from nitrate solution using styryl phosphonate mono-isooctyl ester(SPE108),di-2-ethylhexyl phosphoric acid(D2 EHPA) and 2-ethylhexyl phosphonic acidmono-2-ethylhexyl ester(EHEHPA) as extractants was investigated.The effects of experimental parameters including equilibrium time,extractant concentration,aqueous pH,phase ratio and salt concentration on the extraction process were studied.The results indicate that the extraction ability and capacity of the extractants follow the order:SPE108 D2 EHPA EHEHPA.What's more,the extraction process is less affected by ammonium sulfate in the aqueous phase with SPE108.The results of the separation between lanthanum and adjacent lanthanides(Ce,Pr,Nd,Sm) show that SPE108 can separate lanthanides efficiently at low pH.The extraction mechanism of SPE108 is proved to be similar to D2 EHPA,and the density functional theory(DFT) calculation results infer that SPE108 exhibits superior extraction ability due to its strong electron-accepting ability.     

Study on separation of rare earth elements in complex system

The effect of the feed acidity,acetic acid concentration and rare earth concentration on the distribution ratio,separation coefficient and extraction capacity of light rare earth elements were studied in the P204(DEHPA)-HCl system and P507(HEH/EHP)-HCl system both containing acetic acid,respectively. The results showed that the distribution ratio and separation coefficient decreased with increasing of acidity,and increased with increasing of acetic acid concentration and rare earths concentration,and the extraction capacity increased with increasing of acetic acid concentration. When pH value of feed was 2.0,[RE]/[acetic acid] was 1:1 and rare earth concentration 0.35 mol/L,in P204(DEHPA) -HCl system with acetic acid,the maximum separation coefficient(β) reached to βCe /La=4.09,βPr/Ce=1.96 and βNd/Pr=1.53,and the separation ability of this extraction system was better than P507(DEHPA)-HCl system.     

Solvent extraction of La（III） with 2-ethylhexyl phosphoric acid-2-ethylhexyl ester （EHEHPA） by membrane dispersion micro-extractor

The conventional rare earth solvent extraction equipments have many problems such as long mixing time, low processing capacity, large factory area occupation, high energy consumption and so on. In order to solve the problems, many types of equipments were brought out. In this work, studies were carried out on the La（III） extraction process with 2-ethylhexyl phosphoric acid-2-ethylhexyl ester （EHEHPA） by membrane dispersion micro-extractor. Equilibrium studies showed that the initial aqueous pH value 4.15 with the saponification rate 40%was the optimal operation condition. The effects of membrane dispersion micro-extractor operational conditions such as dispersion mode, bulk flow rate and organic phase flow rate on the extraction efficiency were studied. The results showed that when the organic solution was the dispersed phase, the extraction efficiency was higher than that of others. Increasing bulk flow ratio could enhance the extraction efficiency greatly. When the ratio of organic phase flow rate to that of aque-ous phase was 80：80, the extraction efficiency was over 95%. The effect of stripping phase acidity on the La（III） recovery was studied. The results showed that when the stripping phase pH was 2.0, organic phase flow rate to stripping phase flow rate was 20：80;the re-covery efficiency of La（III） can reach 82%.     

Extraction of selected rare earth elements from anthracite acid mine drainage using supercritical CO_2 via coagulation and complexation

Rare earth elements(REEs) are valuable raw materials which are in great demand in modern high technology industries.Developing methods to produce/recover REEs from waste is significant to the national security of any developed country.This study was focused on investigating the use of supercritical CO2(sCO_2) to extract REEs from anthracite acid mine drainage(AMD).Four different mine drainage water source locations at Blaschak Coal Corp.in Pennsylvania,USA were selected for sample collection.An extraction process was developed and demonstrated for two of those water sources containing the highest concentration of REEs.A method involving metal ion coagulation,their dissolution from the sludge into a concentrated aqueous HNO_3 solution,complexation with organic ligands and sCO_2 extraction was developed to recover REEs from AMD.Specifically,sodium aluminate(NaAlO_2) was used as the coagulant to concentrate REEs from the AMD into a solid precipitate.Consequently,over 99%of the REEs in AMD is concentrated in the remaining sludge.During the coagulation process,the effects of pH and NaAlO_2 concentration on REE precipitation were investigated.Fuming nitric acid(HNO_3) was used to digest the pre-concentrated sludge and tributyl phosphate(TBP) was used to form REE/TBP/HNO_3,a non-polar complex with selected REEs,specifically,cerium(Ce),lanthanum(La) and neodymium(Nd).HNO_3 concentration and organic/aqueous phase ratio were considered as the variables to improve complexation efficiency.Dynamic extraction experiments using sCO_2 and REE/TBP/HNO_3 solutions were then conducted at optimal conditions of 60℃ and 20 MPa.The overall REE extraction efficiencies are found to increase with the atomic number of the REE.As a result,the average overall REE extraction efficiencies of 41.8%,40.1% and 58.2% for Ce,La and Nd,respectively,are obtained.The potential improvements in the overall extraction efficiency are also discussed.     

Analysis of Response Surface in the Study of RE(NO_3)_3-HNO_3-P507-Kerosene Extraction System

RE(NO_3)_3-HNO_3-P507-kerosene extraction system(RE=La,Ce,Pr,Nd,Sm,Eu,Gd,Tb,Dy,Ho,Er,Tm,Yb,Lu,Y)was studied by the response surface technique.14 models for extracting single rare earth ele-ment in a broad range of acidity and initial rare earth concentration were obtained by using the stepwiseregression method.Three-dimensional display of the response surface of the model of extracting Er~(3 )wasshowed as an example,which reveals clearly the dependence of distribution ratio upon both initial acidity and ini-tial rare earth concentration.     

Potential application of graphene oxide and Aspergillus niger spores with high adsorption capacity for recovery of europium from red phosphor,compact fluorescent lamp and simulated radioactive waste

The recovery of rare earth elements(REEs) is a global challenge and the mining of rare earths has serious environmental implications due to the toxic waste released post mining.Hence,the rising demand for rare earths and their far reaching electronic applications necessitates an effective strategy to recover the REEs from more viable sources.In this work,the graphene oxide-Aspergillus niger spores(GO-A.niger spores) blend was utilized for adsorptive recovery of a precious rare earth Eu(Ⅲ) and th...     

A preliminary study of polymer inclusion membrane for lutetium(Ⅲ)separation and membrane regeneration

This paper reports on the selective transport of Lu(Ⅲ) from La(III) and Sm(III) through a polymer inclusion membrane(PIM) composed of 40 wt% di(2-ethylhexyl) phosphinic acid(P227) and 60 wt%poly(vinylidene fluoride)(PVDF).Basically,the changes in surface morphology,thickness and water contact angle of this PVDF-based PIM containing P227(P227@PVDF PIM) with different polymer concentrations were investigated.By solvent extraction experiments,it is found that Lu(Ⅲ) can be selectively extracted from La(Ⅲ) and Sm(Ⅲ) at pH 1.5 in hydrochloric acid solution.According to this result,P227@PVDF PIM was used to selectively transport Lu(Ⅲ) from hydrochloric acid feed solution containing similar concentration of La(Ⅲ) and Sm(Ⅲ).The recovery factor of Lu(III) is 91% after 36 h,and about 5% of Sm(Ⅲ) was also transported through the PIM.The concentration of La(III) in the feed solution and the stripping solution does not change.Furthermore,to overcome the ubiquitous decline of transport efficiency caused by the loss of carrier or the damage of membrane structure after long-term use of PIMs,a process for regenerating PIMs was first proposed and implemented.By comparison of the regenerated PIM with the normal PIM,there is almost no difference in the SEM image,ATR-FTIR spectrum and Lu(III)transport efficiency.It is expected that P227@PVDF PIMs have the potential to be applied to the grouped separation of rare earth elements(REEs),and this study also can be as an inspiration for the further study on the PIMs regeneration process.     

Solvent extraction of rare earth ions from nitrate media with new extractant di-(2,3-dimethylbutyl)-phosphinic acid

As a relatively new extractant, di-(2,3-dimethylbutyl)-phosphinic acid(HYY-2) is more efficient to separate heavy rare earths Tm/Yb/Lu than Cyanex 272 and P507. In this paper, HYY-2 was synthesized in our lab, and the extraction equilibrium, thermodynamics and stripping acidity for La, Gd and Y, which stood for light rare earth elements(REE), middle REE and heavy REE respectively, from nitrate media with this extractant were investigated. Meanwhile, extraction ability, capacity and stripping acidity of HYY-2 were investigated and compared with those of Cyanex 272 and P507. The separation performance for rare earth element couples Gd/Eu and Er/Y were also studied. Compared to Cyanex 272, it possessed higher extraction capacity; while compared with P507, it has lower stripping acidity. The maximum β_(Gd/Eu) 1.46 occurred at pH _(equilibrium)=2.78 and the maximum β_(Er/Y) was 1.47 when pH_(equilibrium)= 2.01.     

Studies on synergistic solvent extraction of rare earth elements from nitrate medium by mixtures of 8-hydroxyquinoline with Cyanex 301 or Cyanex 302

Synergistic solvent extraction of rare earth elements (REEs) from nitrate medium was investigated with mixtures of 8-hydroxyquinoline (HQ) and acidic organophosphorus extractants,bis(2,4,4-trimethylpentyl) dithiophosphinic acid (Cyanex 301) and bis(2,4,4-trimethylpentyl) monothiophosphinic acid (Cyanex 302).The extraction behavior of Cyanex 301/Cyanex 302 and their binary mixtures with HQ towards several lanthanoids (La,Nd,Sm,Tb,Ho,Tm) and yttrium (Y) was investigated.The separation ability of REEs was studied according to the various extraction effects.The extraction mechanisms for yttrium were studied with the methods of slope analysis and constant moles in the synergistic systems.The extracted compounds,the equilibrium constants,and thermodynamic functions were also determined.     

Extraction kinetics of neodymium from chloride medium using HEH/EHP saponified with magnesium bicarbonate solution

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.     

Formation of intermetallic compound at interface between rare earth elements and ferritic-martensitic steel by fuel cladding chemical interaction

The intermetallic compounds formation at interface between rare earth elements and clad material were investigated to demonstrate the effects of rare earth elements on fuel-cladding chemical interaction(FCCI)behavior.Mischmetal(70Ce-30La)and Nd were prepared as rare earth elements.Diffusion couple testing was performed on the rare earth elements and cladding(9Cr2W steel)near the operation temperature of(sodium-cooled fast reactor)SFR fuel.The performance of a diffusion barrier consisting of Zr and V metallic foil against the rare earth elements was also evaluated.Our results showed that Ce and Nd in the rare earth elements and Fe in the clad material interdiffused and reacted to form intermetallic species according to the parabolic rate law,describing the migration of the rare earth element.The diffusion of Fe limited the reaction progress such that the entire process was governed by the cubic rate law.Rare earth materials could be used as a surrogate for high burnup metallic fuels,and the performance of the barrier material was demonstrated to be effective.     

Effects of the accumulation of the rare earth elements on soil macrofauna community

The accumulation of rare earth elements(REEs)in soil has occurred due to the pollution caused by the exploitation of rare earth resources and the wide rare earth fertilizers in agriculture.The accumulation of REEs has a toxic effect on the soil macrofauna community.12study samples were collected near a mine tailings dam with a large amount of REEs by distance gradient sample method.The total concentration of REEs was analyzed and the results were compared with that of the sample from a control site.The effects of the amount of REEs in the soil on the soil macrofauna community were also analyzed.The results showed that the accumulation of REEs in soil was significant in the study area and its concentration was strongly correlated with the distance from the pollution source.One-way ANOVA analysis indicated the significant differences in soil macrofauna communities among the different sites.The ordination obtained through the redundancy analysis demonstrated that the concentration of REEs and the total nitrogen,total potassium and pH,had affected the soil macrofauna community.A small amount of REEs in the soil can promote the diversity of soil macrofauna,but a large amount of REEs can reduce its diversity.The insect groups of Carabidae and Dermaptera were comparatively sensitive to the concentration of REEs in soil,and could be used as an indicator of soil pollution of REEs.However,the Formicidae and Stibaropus formosanus exhibited a high tolerance to REEs in soil.We believe that it is very important for the soil environment protection to strictly control the application of the rare earth fertilizers in agriculture in China.     

A separation processing for industrial rare earth feed solution by phosphonium ionic liquid type saponification strategy

A novel ionic liquid type saponification processing based on quaternary phosphonium type bifunctional IL was developed for yttrium separation from ion-adsorbed rare earth deposit.The extractabilities of([trihexyl(tetradecyl)phosphonium][sec-octylphenoxy acetate]([P_(6,6,6,14)][SOPAA]) were pronouncedly higher than those of sec-octylphenoxy acetic acid(HSOPAA),a mixture of HSOPAA and[P_(6,6,6,14)]Cl for rare earth elements(REEs).The ion association extraction mechanism contributed to avoiding the numerous saponification procedures using alkali and resulting in saponification wastewater.After 13 stages of extraction and 6 stages of scrubbing sections,the Y(Ⅲ) was successfully separated from industrial heavy RREs feed,the purity of Y(Ⅲ) in raffinate was approximately to be 98.9%.Stripping by distilled water was effectively achieved for REEs,which contributed to the decreased consumption of acid to a considerable extent.     

STUDY ON THE SEPARATION AND EXTRACTION MECHANISM OF RARE EARTH ELEMENTS BY MEANS OF REVERSED-PHASE PAPER CHROMATOGRAPHY

Reversed-phase paper chromatography technique is used for study on the extraction mechanism and sep-aration of rare earth elements.As the stationary phase,chromatographic paper strips are impregnated with asolution of monomyristyl phosphoric acid (MPA) in chloroform.Mineral acids are used as developers.The effect of concentration of acids and/or salts upon R_f has been investigated.According to the re-sults of R_f values for a given rare earth element in various acids,the order of extraction ability isHCl>HNO_3>H_2SO_4.A tetrad effect is clearly observed.for the R_f value of rare earth elements.Theeffects of other parameters on the R_f value,such as the quantities of extractant retained by the paper and thetemperature are also examined.Based on the determination of the molar ratio of MPA to rare earth elementsand the number of H~ ions released in extraction reaction,a reasonable mechanism is proposed.The mutualseparation of heavy rare earth elements will be better than that of the light rare earth group because of thelarger separation coefficient of the former.A mixture of Ho-Er-Tm-Lu is successfully separated by thepresent method.     

Characteristic of synergistic extraction of oxalic acid with system from rare earth metallurgical wastewater

Large amount of high concentration acidic wastewater would be produced in the conversion process of chloride rare earth into oxide rare earth.It was a mixed solution of oxalic acid and hydrochloric acid,so the recycling use was very difficult.The method of liquid-liquid extraction was proposed in this paper to achieve wastewater treatment and reclamation.The mechanism of extraction of oxalic acid from the wastewater with the systems of 50% TOB+45% kerosene and 5% 2-ethyl hexanol was investigated.The composition and structure of the extracted species and the establishment of the mathematical model of the oxalic acid extraction were determined by the use of saturation method,equimolar series method.The results showed that extraction of oxalic acid by TOB was a neutral association extraction,oxalic acid existed mainly in a molecular form in the organic phase,and the extraction combination ratio was 2:1.The duality extraction system composed of extractant TOB and TOC had synergistic extraction effect on oxalic acid and chlorhydric acid,and the extraction dislribution ratio was improved greatly.The optimum volume fiaction of TOB was 0.6-0.8.     

Extraction and back-extraction behaviors of 14 rare earth elements from sulfuric acid medium by TODGA

The unique physical and chemical properties of rare earth elements lay the foundation for their extensive application. N,N,N',N' Tetra-octyl-3-oxopentanediamide(TODGA) is excellent in its ability of extracting rare earth elements and it is favored for green initiative. In this paper, the extraction and back-extraction of14 rare earth elements by TODGA were studied. Experiments show that in conditions of 6 mol/L sulfuric acid, the extraction temperature of 25 ℃,the phase ratio of 1:1 and 0.04 mol/LTODGA(aviation kerosene as the diluent), the extraction rates of 14 rare earth elements including lanthanum, cerium, praseodymium,neodymium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, and yttrium were 99.00%-99.73%. Mixed with hydrochloric acid and nitric acid(HCl 3.5 mol/L, HNO_30.5 mol/L), the recoveries of the 14 rare earth elements are 91.52%-99.91% when the extraction temperature is 25 ℃ and the ratio is 1:1. The following application is based on the optimum conditions above with practical samples(from the roasting production line of China North Rare Earth High-tech Company Limited) for extraction and back-extraction experiments. Experiments show that TODGA has excellent enrichment effect on 14 rare earth elements, the extraction rates are 91.36%-99.80%, the back-extraction rates are 87.29%-99.64% and the total recoveries are 81.19%-99.44%.     

Study on transport of Dy(Ⅲ) by dispersion supported liquid membrane

The transport of Dy(Ⅲ) through a dispersion supported liquid membrane (DSLM) consisting of polyvinylidene fluoride mem-brane (PVDF) as the liquid membrane support and dispersion solution including HC1 solution as the stripping solution and 2-ethyl hexyl phosphonic aeid-mono-2-ethyl hexyl ester (PC-88A) dissolved in kerosene as the membrane solution, was studied. The effects of pH value, initial concentration of Dy(Ⅲ) and different ionic strength in the feed phase, volume ratio of membrane solution and stripping solution, con-centration of HC1 solution, concentration of carder, different stripping agents in the dispersion phase on transport of Dy(Ⅲ) were also inves-tigated, respectively. As a result, when the concentration of HCI solution was 4.0 mol/L, concentration of PC-88A was 0.10 mol/L, and vol-ume ratio of membrane solution and stripping solution was 40:20 in the dispersion phase, and pH value was 5.0 in the feed phase, the trans-port effect of Dy(Ⅲ) was the best. Ionic strength had no obvious effect on transport of Dy(Ⅲ). Under the optimum condition studied, when initial concentration of Dy(Ⅲ) was 0.8×10-4 mol/L, the transport rate of Dy(Ⅲ) was up to 96.2% during the transport time of 95 min. The kinetic equation was developed in terms of the law of mass diffusion and the theory of interface chemistry. The diffusion coefficient of Dy(Ⅲ) in the membrane and the thickness of diffusion layer between feed phase and membrane phase were obtained and the values were 1.99×10-7 m2/s and 15.97 μm, respectively. The results were in good agreement with experimental results.     

One-step separation and recovery of rare earth and iron from NdFeB slurry via phosphoric acid leaching

The recovery of rare earth elements(REEs)from NdFeB slurry by traditional hydrometallurgy has been limited becuase a large number of REEs are lost during separation together with iron.In this paper,a simple and sustainable method is proposed to efficiently separate and recover REEs and iron from NdFeB slurry.REEs were recovered by one-step selective precipitation in phosphoric acid,and the dissolved iron was recovered by oxalic acid.Phosphoric acid leaching results show that under the conditions of 4 mol/L phosphoric acid,80℃,L/S of 30:1 and 90 min,the leaching efficiencies of Fe and REEs reach 98.76%and1.09%,respectively.While the rest of REEs remained in the leaching residue in the form of REEPO₄·nH₂O precipitation.Subsequently.the mixed rare earth oxide(rare earth oxalate roasted at 800℃)and FeC₂O₄·2 H₂O are obtained by oxalic acid precipitation with purities of 99.49%and 97.17%from the REEPO4·nH₂O dissolving solution and the phosphoric acid leaching solution.Moreover,the phosphoric acid is regenerated while recovering iron,and it can be reused in the phosphoric acid leaching step after removing the impurity C₂O₄^2-.In summary,this work provides an efficient and environmentally friendly method for recovering REEs and iron from NdFeB slurry waste.