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.     

Separation of Eu（III） with supported dispersion liquid membrane system containing D2EHPA as carrier and HNO3 solution as stripping solution

The Eu(III) separation in supported dispersion liquid membrane (SDLM),with polyvinylidene fluoride membrane (PVDF) as the support and dispersion solution containing HNO3 solution as the stripping solution and Di(2-ethylhexyl) phosphoric acid (D2EHPA) dis-solved in kerosene as the membrane solution,was studied.The effects of pH value,initial concentration of Eu(III) and different ionic strengths in the feed phase,volume ratio of membrane solution and stripping solution,concentration of HNO3 solution,concentration of carrier,different stripping agents in the dispersion phase on the separation of Eu(III) were also investigated,respectively.As a result,the optimum separation conditions of Eu(III) were obtained as the concentration of HNO3 solution was 4.00 mol/L,concentration of D2EHPA was 0.160 mol/L,and volume ratio of membrane solution to stripping solution was 30:30 in the dispersion phase,and pH value was 5.00 in the feed phase.Ionic strength had no obvious effect on the separation of Eu(III).Under the optimum conditions studied,when initial concentration of Eu(III) was 1.00×10–4 mol/L,the separation rate of Eu(III) was up to 94.2% during the separation period of 35 min.The kinetic equation was developed in terms of the law of mass diffusion and the theory of interface chemistry.The results were in good agreement with the literature data.     

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.     

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.     

Effect of loaded organic phase containing mixtures of silicon and aluminum, single iron on extraction of lanthanum in saponification P507-HCl system

Emulsification troubled normal extraction process of rare earths due to the existence of non-rare earth impurities,especially Si,Al and Fe.Against this background,the effect of emulsification caused by Si,Al and Fe on the La extraction with saponification P507(2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester) in chloride medium was systematically investigated.A series of experiments were carried out to study the relationship of the extraction capacity of La and the concentration of impurities.ZPM-203 polarizing microscope was applied to investigate the morphology of emulsification,and the cation exchange extraction mechanism of Fe and Al as well as La was clarified by IR spectra.The results showed that a low concentration of Si in organic phase would aggravate the emulsification with Al,and the formation of ME(micro emulsion) and club-shaped polymer would result in emulsification in the extraction of mixtures of Si and Al,single Fe,respectively.Furthermore,the accumulation of impurity such as Si,Al and Fe in the organic phase would severely reduce the extraction capacity of La simultaneously.     

New Environment-Friendly Approach for Bastnasite Metallurgic Treatment （Ⅰ）： Extraction of Tetravalent Cerium from Sulphuric Acid Medium with Di（2-ethylhexyl） Phosphoric Acid

The extraction of cerium （Ⅳ) from sulphuric acid medium with Di(2-ethylhexyl) phosphoric acid (DEHPA) was studied. The influence of sulphate ion, acidity, extractant concentration as well as the presence of fluoride ion on the extraction of Ce(Ⅳ) was investigated, and the extraction mechanism was also discussed. The results show that sulphate ion can inhibit the extraction of Ce(Ⅳ) significantly due to its complexation with Ce(Ⅳ). Fluoride ion can enhance Ce(Ⅳ) extraction dramatically by the formation of CeF2^2 and less amount of CeF^3 which can almost be extracted completely. Nevertheless, in the case as F/Ce(mole ratio) in the initial aqueous phase is approximately more than 1.5, the precipitate will be formed and the extraction can not be progressed smoothly.     

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.     

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.     

Synergistic extraction of rare earth by mixtures of 2-ethylhexyl phosphoric acid mono-2-ethylhexyl ester and di-（2-ethylhexyl） phosphoric acid from sulfuric acid medium

The extraction of Nd^3＋ and Sm^3＋, including the extraction and stripping capability as well as the separation effect of Nd^3＋ or Sm^3＋, from a sulfuric acid medium, by mixtures of di-（2-ethylhexyl） phosphoric acid （HDEHP, H2A2（0）） and 2-ethylhexyl phosphoric acid mono-2-ethylhexyl ester （HEH/EHP, H2L2（0）） were studied. The distribution ratios and synergistic coefficients of Nd^3＋ and Sm^3＋ in different acidities were also determined. A synergistic extractive effect was found when HDEHP and HEH/EHP were used as mixed extractants for Sm^3＋ or Nd^3＋. The chemical compositions of the extracted complex were determined as Nd.（HA2）2-HL2 and Sm.（HA2）2-HL2. The extraction equilibrium constants, enthalpy change, and entropy change of the extraction reaction were also determined.     

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.     

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.     

Nonlinear current-voltage characteristics originated from phase segregation and micro-cracks in polycrystalline La_（0.67）Ba_（0.33）MnO_3

Polycrystalline La0.67Ba0.33MnO3 bulk samples were annealed in flowing 95%Ar:5%H2 (AH) mixed gas at 973 K for different time respectively. The influence of the annealing time on the current-voltage properties was systematically investigated. Linear current-voltage characteristics were observed in the as-prepared and the 10 h annealed samples, and nonlinear current-voltage characteristics was found in the 100 h annealed sample. At the same time, segregation of impurity phase and micro-cracks were found on the surfaces of the 100 h annealed samples, which was testified to be Ba ion impurity. Analysis showed that the changes of electronic properties were caused by barium ion im-purities and micro-cracks in the 100 h annealed sample.     

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.     

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 non-saponification extraction process for rare earth separation

The purpose of this study was to overcome the disadvantages of ammonia-nitrogen wastewater pollution and high cost of sodium saponification in rare earth separation process. The study focused on the non-saponification extraction technology with magnesia. The influences of the content and particle size of magnesia, reaction time, reaction temperature, and O/A on cerium extraction rate were also discussed. The results showed that the hydrogen ions of extractant were exchanged by rare earth ions when organic extractant and rare earth solution were mixed with magnesia powder, and then the exchanged hydrogen dissolved magnesia to make the acidity of the system stable. The magnesium ions were not participated in the extraction reaction. Non-saponification extraction process of rare earth had been realized. The cerium extraction rate could reach up to 99% in single stage within the optimal reaction conditions.     

Structure and high-temperature electrochemical properties of La_（0.60）Nd_（0.15）Mg_（0.25）Ni_（3.3）Si_（0.10） hydrogen storage alloys

The structure and high-temperature electrochemical properties of the as-cast and annealed (940 °C, 8 h) La0.60Nd0.15Mg0.25Ni3.3Si0.10 hydrogen storage alloys were investigated. The X-ray diffraction revealed that the multiphase structure of the as-cast alloy with LaNi5 phase as the main phase was converted into a double-phase structure with La2Ni7 phase as the main phase after annealing. The surface morphology studied by scanning electronic microscope (SEM) showed that the annealed alloy had a much higher anti-corrosion ability than the as-cast alloy. Both alloys presented excellent activation characteristics at all test temperatures. The maximum discharge capacity of the as-cast alloy decreased when the test temperature increased, while the temperature almost had no effect on the annealed alloy. As the test temperature increased, the cyclic stability and charge retention of both alloys decreased, and these properties were improved significantly by annealing.     

Study on preparation and application of novel saponification agent for organic phase of rare earths extraction

In view of the problem of ammonia-nitrogen wastewater pollution in rare earths extraction and separation, the novel saponification agent of organic phase, which is magnesium bicarbonate solution, was prepared with the natural rich and cheap dolomite as raw material through carbonation process. The behavior and purification of main impurities ions in the carbonation process as well as the application effect of the novel saponification agent in the extraction and separation was researched. The results showed that the concentration of Fe, Al, Si impurities ions was less than 5 ppm in the saponification agent through the development of effective removal technology, respectively. When the novel saponification agent was used in the extraction and separation, magnesium utilization rate was more than 95%, and rare earths extraction rate above 99.5% has achieved. Therefore, the technology could replace ammonia-water to saponify the organic phase in rare earth extraction and separation process.     

Studies on electrical properties and CO-sensing characteristics of La_（0.9） _（0.1）FeO_3

Semiconducting sensors offer an inexpensive and simple method for monitoring gases. Sensors based on the ABO3-type composite oxides materials have an advantage of high stability. The perovskite structures of these compounds are preserved, when an A-site deficiency of some perovskite structure compounds was formed. However, they exhibit particular physical properties. In this paper, La0.9 0.1FeO3 powder with an orthorhombic perovskite phase was prepared by sol-gel method. The electrical properties and CO-sensing characteristics of the La0.9 0.1FeO3 were also investigated. The results demonstrated that the La0.9 0.1FeO3 was a p-type semiconductor material. Compared with LaFeO3, the conductance of La0.9 0.1FeO3 was better than that of LaFeO3. The sensor based on La0.9 0.1FeO3 showed excellent CO gas-sensing characteristics.     

Preparation and CO conversion activity of ceria nanotubes by carbon nanotubes templating method

Ceria nanotubes with high CO conversion activity by means of carbon nanotubes as removable templates in the simple liquid phase process were fabricated under moderate conditions. The pristine CNTs were first pretreated by refluxing in a 30% nitric acid solution at 140 ℃ for 24 h, then dispersed in an ethanolic Ce（NO3）3.6H2O solution with ultrasonic radiation at room temperature for 1 h. Under vigorous stirring, NaOH solution was added drop by drop into the above ethanolic solution until the pH value was 10. The product was collected and repeatedly washed with ethanol and on drying at 60 ℃, the CeO2/CNT composites were obtained. Then, the as-prepared composites were heated at 450 ℃ in an air atmosphere for 30 min to remove CNTs. The ceria nanotubes were characterized by X-Ray Diffraction （XRD）, Transmission Electron Microscopy （TEM）, and X-Ray Photoelectron Spectrum （XPS）. The results showed that the ceria nanotubes were polycrystalline face-centered cubic phase and were composed of lots of dense cefia nanoparficles. The diameter of cefia nanotubes was about 40-50 nm. Catalytic activity of the product for CO oxidation was carded out at the region of 30-300 ℃ in a U-shaped quartz reactor with feeding about 0.15 g of the catalyst, which was loaded on Al2O3 carder. The inlet gas composition was 1.0% CO and 28% O2 with N2 as balance, and the rate of flow was kept at 40 ml/min. The catalytic products were analyzed by gas chromatography. The as-repared CeO2 nanotubes showed higher CO oxidation activity, which indicated that the morphology of ceria products affected the catalytic performance. The ceria nanotubes supported on Al2O3 demonstrated that conversion temperature for CO oxidation to CO2 was lower than that for bulk catalysts.     

Hydrogen storage properties of mechanically milled La2Mg17-x wt.% Ni （x=0, 50, 100, 150 and 200） composites

Melting method was used to obtain La2Mg17 alloy,and then Ni powder was added by mechanical alloying method.The kinetics of hydriding process and electrochemical properties of La2Mg17-x wt.%Ni(x=0,50,100,150,200) composites were investigated.X-ray diffraction(XRD) and scanning electron microscopy(SEM) analyses showed that the crystal structure of composite alloy gradually transformed into amorphous phase by the effect of ball milling and Ni powders.The research of hydrogen absorption properties found that La2Mg 17-50 wt.%Ni reached the highest hydrogen absorption than other alloys with more addition of Ni content,reached to 5.796 wt.% at 3 MPa,and up to 5.229 wt.% merely in 2 min,which revealed that the amorphous phase reduced the H occupation of the lattice clearance,resulting in the decline of hydrogen absorption capacity.The electrochemical tests indicated that the maximum discharge capacity increased to 353.1 mAh/g at 30 oC,however,the cycle stability decreased considerably.A series of kinetic measurements demonstrated that the controlling steps of electrochemical process of La 2 Mg 17-x wt.%Ni alloys transferred from hydrogen diffusion on alloy bulk(x=50,100) to hydrogen diffusion on both alloy bulk and surface(x=150,200).