Study on a novel flat renewal supported liquid membrane with D2EHPA and hydrogen nitrate for neodymium extraction

The Nd(III) extraction in flat renewal supported liquid membrane(FRSLM),with polyvinylidene fluoride membrane and renewal solution including HNO3 solution as the stripping solution and di(2-ethylhexyl) phosphoric acid(D2EHPA) dissolved in kerosene as the membrane solution,was investigated.The effects of pH in the feed phase,volume ratio of membrane solution to stripping solution,concentra-tion of HNO3 solution and concentration of carrier in the renewal phase on extraction of Nd(III) were also studied,respectively.As a result,the optimum extraction conditions of Nd(III) were obtained when concentration of HNO3 solution was 4.00 mol/L,concentration of D2EHPA was 0.100 mol/L,and volume ratio of membrane solution to stripping solution was 1.00 in the renewal phase,and pH was 4.60 in the feed phase.When initial concentration of Nd(III) was 2.00×10-4 mol/L,the extraction percentage of Nd(III) was up to 92.9% in 75 min.     

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.     

Efficient extraction and stripping of Nd(Ⅲ),Eu(Ⅲ) and Er(Ⅲ) by membrane dispersion micro-extractors

The extraction of low concentration rare earth elements at high phase ratio was investigated. The traditional extraction set-up, such as mixer-settler, have drawbacks of easy emulsification, difficult separation and low efficiency if operated at the above condition. Membrane dispersion micro-extractor,owing to its well-dispersed, high surface-to-volume ratio and fast mass transfer rate, was employed in our work. Nd(Ⅲ),Eu(Ⅲ),Er(Ⅲ) were chosen to represent light, medium,heavy rare earth elements(REEs). The extraction process of REEs with 2-ethylhexyl phosphoric acid-2-ethylhexyl ester(P507) was investigated by membrane dispersion micro-extractors. Firstly, the extraction equilibrium of these three elements was explored in the stirred conical flasks, and it is indicated that the extraction efficiencies can be 0.95, 0.97 and 0.98, respectively within 40 min at phase ratio of 100:1. Then the effects of operational conditions such as the residence time, organic and aqueous flow rates on extraction efficiency were also explored in micro-extractors. The results indicate that the efficiency decreases and then increases if increasing aqueous phase flow rate, residence time and droplets' diameter are the key factors of this process. Increasing the phase ratio reduces the extraction efficiency significantly. When the REEs solution has an initial pH of 4.00, the flow rates of continuous and dispersed phase are 40 and 1.6 mL/min,respectively, and 90 mg/L Nd(Ⅲ), Eu(Ⅲ) and Er(Ⅲ) is extracted by 1 mol/L P507 at the out-let length of8 m. The extraction efficiencies are 0.978,0.983 and 0.991, respectively. Finally the stripping process was also studied with the micro-extractor. The stripping efficiencies of Nd(Ⅲ), Eu(Ⅲ) and Er(Ⅲ) can reach0.99, 0.96 and 0.91, respectively when the out-let length is 8 m and the concentration of hydrochloric acid is 1 mol/L. The developed approach offers a novel and simple strategy on the fast extraction and enrichment of low concentration rare earth elements from waste water.     

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%.     

Study on thorium recovery from bastnaesite treatment process

Thorium (Th) stripping behavior from HEH/EHP (2-(ethylhexyl) phosphoric acid mono-2-ethylhexyl ester) with H2SO4, HCl and HNO3 were investigated. The results indicated that H2SO4 was the most effective stripping reagent compared with HCl and HNO3. Selecting H2SO4 as the stripping reagent, the effect of phase ratio, acidity, H2SO4 amount, HEH/EHP concentration and Th loading in HEH/EHP on Th stripping were systematically investigated. As a result, the optimum stripping conditions of Th(IV) were obtained as the concentration of H2SO4 solution was 3.50 mol/L, phase ratio was 4:1. Low HEH/EHP concentration was benefit for Th stripping. Based on the results, pilot test for new Bastnaesite treatment process was carried out and the recovery of Ce, F and Th were more than 99%, 98% and 95% separately.     

Comparative studies on Y(Ⅲ)and Dy(Ⅲ)extraction from hydrochloric and nitric acids by Cyanex 572 as a novel extractant

Extraction of Y(III) and Dy(III) from hydrochloric and nitric acids by Cy-572 in kerosene was studied. The factors affecting the extraction were separately investigated. The stoichiometry of the extracted species was deduced on the basis of slope analysis method. Evaluation of extraction equilibrium and stripping investigation was studied as well as saponification effect of Cy-572. The composition of the extracted metal species in the organic phase was found to be [MA_3·(HA)_3] for Y(III) or Dy(III) in both media.1.0 mol/L HCI is the best stripping agent for each metal ion from the studied acidic media in one step.Saponified Cy-572 does not exhibit any selectivity towards the extraction of Y(III) or Dy(III) from both HCI and HNO_3 solutions. Based on the obtained results, the data were compared and the separation feasibility between lanthanides and Y(III) in the two media was discussed.     

Application of nanofiltration to treat rare earth element （neodymium） containing water

The scope of present work was to study the feasibility of a commercial nanofiltration(NF) membrane to reject Nd(III) ions fromsynthetic aqueous solution.The permeates were analyzed using inductively coupled plasma-atomic emission spectrometry(ICP-AES) to findNd(III) concentration.Experimental results indicated that the Nd(III) rejection increased with increase in applied pressure and feed flow rate;and decreased with increase in feed concentration.Rejection of Nd(III) ions using NF membrane were widely influenced by solution pH dueto the charged nature of the membrane which changed with the variation in pH.The use of a surfactant(sodium dodecyl sulphate) in aqueoussolution resulted in its adsorption on the membrane surface,thereby changing membrane characteristics,and in turn influencing the rejection.The complexation step induced had also increased the rejection to a greater extent by forming [Nd-EDTA]-complex thereby increasing itsmolecular weight and thus increasing rejection.     

Solvent extraction of neodymium（III） from acidic nitrate medium using Cyanex 921 in kerosene

The extraction of neodymium(Ⅲ) from acidic nitrate medium was investigated using Cyanex 921 as extractant in kerosene. The metal concentration in the aqueous phase before and after extraction was determined spectrophotometrically by Arsenazo Ⅲ method. The complete equilibration was achieved in 15 min. The effects of shaking time, nitric acid concentration, nitrate concentration, extractant concentration, and temperature on the extraction were studied. The extraction of Nd(Ⅲ) was found to increase very slowly with increase in concentration of HNO3 in the range of 0.001-0.008 mol/L and then decreased when 0.01 mol/L HNO3 was used. The percentage of extraction was increased with increase in nitrate concentration from 0.01-0.45 mol/L and then decreased when nitrate concentration increased to 0.5 mol/L. Quantitative extraction of Nd(Ⅲ) (98%) was obtained from the aqueous phase containing 0.001 mol/L HNO3 and 0.1 mol/L KNO3 using 0.5 mol/L Cyanex 921. On the basis of slope analysis, the extracted complex in the organic phase was proposed to be Nd(NO3)3.2Cyanex 921. The extraction of Nd(III) was found to increase with increase in concentration of metal ion in the range of 0.001-0.05 mol/L from 0.001 mol/L HNO3 and 0.1 mol/L KNO3 with 0.1 mol/L Cyanex 921. The percentage of extraction of neodymium was found to decrease with increase in temperature. From temperature variation studies, the negative value of △H indicated the extraction reaction to be exothermic and the negative value of △S indicated the formation of a stable complex. Almost 100% Nd(Ⅲ) was recovered from the fully loaded organic phase using 0.002 mol/L H2SO4 and 0.01 mol/L HCl.     

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.     

New Methodological Approach to Investigation of Kinetics of REE Extraction in Nonstationary Conditions

The influence of periodical oscillations of the temperature on extraction and stripping processes in the extraction systems was studied. Two extraction systems were investigated： （1） 6 mol · L^-1 NaNO3-Nd（NO3）3-Pr（NO3）3-TBP kerosene and （2） [Nd（NO3）3 · 3TBP] -[ Pr（NO3）3 · 3TBP] -kerosene - 0.1 mol · L^-1 HNO3. Mathematical modeling of the nonstationary membrane extraction has been enhanced by including the dependence of the extraction rate constants on temperature. The values of activation energy for direct and reverse extraction and stripping reactions of Pr and Nd were calculated from experimental temporal dependencies of metal concentration and temperature by solving the reverse kinetics problem using the proposed mathematical model, A series of experiments with periodical oscillations of the temperature on the extraction system for the separation of rare earth elements （REE） using bulk liquid membrane between two extractors were performed. The mathematical model adequately describes the experimental data. The optimization of the extraction process for separation of REE by liquid membrane, under the influence of periodical oscillation of the temperature, was made based on the extraction rate constants and activation energies. The optimal conditions of separation by liquid membrane were found： frequency and amplitude of thermal oscillations, liquid membrane flow rate, and optimal ratio between organic and aqueous phase in extractors.     

Luminescence study of europium(III) tris(β-diketonato)/phosphonate complexes in chloroform

The extraction of Eu(III) with β-diketone, HA, and monodentate or bidentate Lewis bases, B, into chloroform and the luminescence properties of the extracted species were studied. Pivaloyltrifluoroacetone, Hpta, and 2-thenoyltrifluoroacetone, Htta, were used as the β-diketones. The Lewis bases, B, were tetraethyl methylene diphosphonate, POPO, which was bidentate, and diethyl benzylphosphonate, PhPO which was monodentate. Based on the extraction data, the stability constants, log β of the first complexes between tris(β-diketonato)Eu(III) and the phosphonate, EuA3B, were determined to be 6.0 for the POPO complex and 3.40 for the PhPO complex. The Eu(III) luminescence intensity in the EuA3POPO was larger than EuA3 where A was either pta or tta at similar concentrations of Eu(III), while that in Eu(pta)3PhPO was stronger than EuA3; however, in Eu(tta)3PhPO, it was weaker than Eu(tta)3. The POPO functions as a sensitizer, and the PhPO functions as a quencher for the tta chelate and as a sensitizer for the pta chelate. From the lifetime and quantum yield, φ, of the Eu(III) luminescence in the complexes as well as the observation of the extractability of Eu(III) with the Hpta and the phosphonates and of the luminescence spectra of the complexes, it was confirmed that the extraction of Eu(III) was remarkably enhanced with a β-diketonate and a strong Lewis base, and also the ternary complex that was formed as the extracted species, showed luminescence enhancement. This phenomenon may be due the formation of a strong bond between the Eu(III) and the strong Lewis base leading to more hydrophobicity in the extracted species and also to more effective energy transfer from the Lewis base to the Eu(III). It was not significant whether the donor atoms were N or O.     

Study on the adsorption of lanthanum(Ⅲ) from aqueous solution by bamboo charcoal

The adsorption behaviors of La(Ⅲ) ion on bamboo charcoal were investigated with various chemical methods and IR spectrometry. Parameters studied include the effects of pH,average particle size,initial ion concentration,contact time and temperature by batch method. The results showed that bamboo charcoal could remove La(Ⅲ) ions effectively from aqueous solution. The loading of La(Ⅲ) ions was strongly dependent on pH of the medium and the optimal adsorption condition was in HNO3-TEA medium with pH value of 7.20. In the batch system,the modified bamboo charcoal exhibited the highest La(Ⅲ) ion uptake as 120 mg/g at 298 K,at an initial pH value of 7.20. The adsorption kinetics were tested with Lagergren-first-order model and pseudo-second-order model. The adsorption data were conformed to the Langmuir and Freundlich isotherms,and the correlation coefficients had been evaluated. Thermodynamic parameters such as free energy(ΔG) ,which were all negative,indicated that the adsorption of La(Ⅲ) ion onto bamboo charcoal was spontaneous and the positive value of enthalpy(ΔH) showed that the adsorption was endothermic in nature. Thomas model was applied to experimental column data to determine the characteristic parameters of column useful for process design. The characterization of both before and after adsorption of La(Ⅲ) ion on bamboo charcoal was undertaken using IR spectroscopic technique. The results revealed that bamboo charcoal was a good choice as a biosorbent for the recovery of lanthanum from aqueous solution.     

Minimum amount of extracting solvent of AB/BC countercurrent extraction separation using organic feed

For an AB/BC countercurrent extraction separation using organic feed, the conditions to have minimum amount of ex- tracting solvent （Smin） and minimum amount of scrubbing agent solution （Wmin） were discussed, and the formulae of both Sroin and Wmin were deduced. It was shown that only when the ratio of flowrate of central component B leaving aqueous outlet to that leaving organic outlet took a certain optimal value, the AB/BC separation could have Smin as well as Wmin, and this optimal ratio was decided by the separation factors between the three components but independent of feed composition. Smin was only relative to the separation factor of A/C pair but regardless of the separation factors of other pairs as well as feed composition, whereas Wmin was determined by the separation factors between the components together with feed composition. Meanwhile it was also found that the organic stream out of feed stage was same composition as the initial organic feed when the separation system was given by the two minimum amounts and its steady state was achieved. Finally the results above were used to design a LuYb/YbTm separation case and the stage-wise compositions of each component in both the organic and the aqueous phase at steady state were given by computer simulation.     

Evaluation of D113 cation exchange resin for the removal of Eu(Ⅲ) from aqueous solution

Batch adsorption experiments were conducted for the adsorption of Eu(Ⅲ) ions from aqueous solution by D113 resin. The results indicated that D113 resin could adsorb Eu(Ⅲ) ion effectively from aqueous solution. The adsorption was strongly dependent on pH of the medium with enhanced adsorption as the pH turned from 3.50 to 7.00 and the optimal adsorption condition was in HAc-NaAc medium with pH value of 6.50. The maximum uptake capacity of Eu(Ⅲ) ions was 290.9 mg/g D113 at 298 K, at an initial pH value of 6.50. The overall adsorption process was best described by Lagergren-first-order kinetics. When Freundlich and Langmuir isotherms were tested, the latter had a better fit with the experimental data. The thermodynamic parameters such as free energy (G) which were all negative, indicated that the adsorption of Eu(Ⅲ) ions onto D113 resin was spontaneous and the positive value of enthalpy (H) showed that the adsorption was endothermic in nature. Thomas model was applied to experimental column data to determine the characteristic parameters of column useful for process design. Furthermore, Eu(Ⅲ) could be eluted by using 3.0 mol/L HCl solution and the D113 resin could be regenerated and reused.     

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 technology of Pr and Nd in D₂EHPA-HCl-LA coordination extraction system

The separation coefficient of Nd/Pr was lower in D2EHPA-HCl system. Pointing to this problem,the effect of the acidity of feed and the concentration of lactic acid on the distribution ratio,separation coefficient and extraction capacity was investigated in unsaponified D2EHPA-HCl-LA system,and the regression equations were calculated in this paper. The results showed that the distribution ratio and separation coefficient both increased with decreasing of feed acidity and increasing of the lactic acid concentration,and the extraction capacity increased with increasing of lactic acid concentration in D2EHPA-HCl-LA system. When the pH value of the feed was 3.5 and lactic acid concentration was 0.6 mol/L,the max separation coefficient was 1.57,and the extraction capacity was 27.87 g/L.     

Extraction and separation of Nd(Ⅲ), Sm(Ⅲ), Dy(Ⅲ), Fe(Ⅲ), Ni(Ⅱ), and Cs(Ⅰ) from concentrated chloride solutions with N,N,N’,N’-tetra(2-ethylhexyl) diglycolamide as new extractant

The feasibility of using N,N,N’,N’-tetra(2-ethylhexyl)diglycolamide(TEHDGA) in 75 vol.% n-dodecane-25 vol.% n-octanol as agents for the extraction and separation of Nd(III), Sm(III), Dy(III), Fe(III), Ni(II), and Cs(I) from concentrated chloride solution was investigated. Different extraction behaviors were obtained towards rare earth elements(REE) studied and Fe(III), Ni(II) and Cs(I). Efficient separation of Nd(III), Sm(III) and Dy(III) from Fe(III), Ni(II), and Cs(I) was achieved by TEHDGA, depending on the HCl, HNO3 or H2SO4 concentration. A systematic investigation was carried out on the detailed extraction properties of Nd(III), Sm(III), and Dy(III) with TEHDGA from chloride media. The IR spectra of the extracted species were investigated.     

Adsorption behavior of ytterbium (Ⅲ) on gel-type weak acid resin

The adsorption and desorption behaviors of Yb(Ⅲ) on gel-type weak acid resin (110) were investigated. The influence of operational conditions such as contact time,initial concentration of Yb(Ⅲ),initial pH of solution and temperature on the adsorption of Yb(Ⅲ) were also examined. The results showed that the optimal adsorption condition of 110 resin for Yb(Ⅲ) was achieved at pH=5.5 in HAc-NaAc medium. The maximum uptake capacity of Yb(Ⅲ) was 265.8 mg/g at 298 K. Yb(Ⅲ) could be eluted by using 3.0 mol/L HCl solution and the 110 resin could be regenerated and reused. The adsorption of Yb(Ⅲ) followed the Langmuir isotherm,and the correlation coefficients were evaluated. Various thermodynamic parameters such as standard enthalpy change (△H),standard entropy change (△S) and standard free energy change (△G) were evaluated. The adsorption of Yb(III) on the 110 resin was found to be endothermic in nature. Thomas model was successfully applied to experimental data to predict the breakthrough curves and to determine the characteristics parameters of the column useful for process design. And the resin sample both before and after adsorption was described by IR spectroscopy.     

Controlled synthesis and tunable luminescence of NaYF₄:Eu³⁺

High quality NaYF4:Eu3+ luminescent materials were successfully synthesized via a facile template technique by hydrothermal method.The samples were characterized by X-ray powder diffraction(XRD),transmission electron microscopy(TEM) and fluorescence spectroscopy(FS).The incorporating of Eu3+ ions into NaYF4 crystal lattice influenced the symmetry types of NaYF4 crystals,resulting in phase transformation of NaYF4 crystals between α and β phase.The pure hexagonal phase of branched NaYF4:Eu3+ was obtained as the Eu3+ concentration reached 15 mol.%.In addition,the luminescence color was tuned by changing the doping concentration of Eu3+ ions.     

Direct Spectroscopic Determination of Europium(Ⅱ) Concentration During Europium(Ⅲ) Electro-Reduction in Hydrochloric Acid Medium

UV-Vis spectroscopy was used to directly determine the concentration of Eu(Ⅱ) during electroreduction of Eu(Ⅲ) in hydrochloric acid medium. Electroreduction was carried out in a flow type electrolyzer with glassy carbon cathode at the constant potential of -800 mV vs. Ag/AgCl. The effects of oxygen and concentration of hydrochloric acid on the system were investigated. For 0.01 mol·L-1 hydrochloric acid, calibration curves for Eu(Ⅱ) absorption bands at 248 and 320 nm were constructed. Molar absorption coefficients were estimated to be 2016 and 648 L·mol-1·cm-1, respectively. The absorbance strongly decreased with decrease in pH of the solution, whereas concentration of chloride had only a negligible effect.