Purification of Yb2O3 and Lu2O3 by Extraction Chromatography Using 2-ethylhexyl 2-ethylhexylphos-phonate Resin

D0I:10.13374/j.issm1001-053x.1991.05.017 第13卷第5(1)期 北京科技大学学报 Vol,13No.5(I) 1991年9月 Journal of University of Science and Technology Beijing Sept,1991 Purification of Yb2O,and Lu,Os by Extraction Chromatography Using 2-ethylhexyl 2-ethylhexylphos- phonate Resin Fan Limin·Shen Fengyun'Wang Wencheng·- (沈利民) (沈风韵) (汪文成) ABSTRACT:The optimum conditions for extraction chromatography using 2ethyl- hexyl 2-ethylhexylphosphonate resin to separate thulium,yetterbium and luticium were studied.According to the proposed procedure,several grams of yetter- bium oxide (purity=99.95%)and luticium oxide (purity =99.90%)were separa- ted from the mixed heavy rare earth oxides on laboratory scale.Their relatively high recoveries (99%and 95%for.Yb2O3 and Lu2Os respectively)may be sa- tisfactory KEY WORDS:separation,extraction chromatography,purification,yetterbium, luticium,2-ethylhexy1 2-ethylhexylphosphonate, It is noted that the separation of single rare earth one by one are still sel- dom found from the literatures.Because the eluting curves for the neighbouring rare earth especially the heavy ones are always reduplicated with each other(, they are difficult to separate thoroughly from each other and can hardly be used for the purification of single rare earth.Furthermore,it was also noted that method of separating yetterbium and luticium has not been reported any- where else,Yetterbium and luticium has been considered as one of the most di- fficult pairs of rare earths to separate.With conventional solvent extraction,the separation factor stays around 1.2 to 1.5 with different extraction systems. Manuscript Received oct.18,1990 .Department of Chemistry in USTB .Chief Eagineer's office,Yuelong Chemical Plant,Shanghai 498

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That means at least more than 100 stages would be required.With conventional ion exchange technique,both EDTA and HEDTA would be required and these chelating agents are all highly expensive. From the extraction chromatographic study,the authors found that the elu- ting curves of many neighbouring rare earths can be clear-cut with a suitable extractant resin under controlled conditin,and succeeded in developing a pro- cedure for the separation of Tm,Yb and Lu before the spectrophotometric de- termination of single Yb and Lut2).Heace an atiempt to study their separation to apply on the preparation of pure Yb2O3 and Lu2O3 was coming across our mind. 1 Experimental 1.1 Apparatus and Reagents 3 glass columns (/L=16mm/250mm,16mm/520mm and 11mm/700mm) with a constant temperature jacket used for chromatography. A 501 type superior constant temperaturt regulator,used to control the temperature。 2-ethyhexyl 2-ethylhexyl phosphonate (initialism HEHCEHP);and its commercial name P-507 in China and PC-88 in Japan)resin,synthetized by ourselves,which contained 55%HEHCEHP]with a saturated capacity of 1.7 mmol/g (dry resin),a heap density of 0.47g/ml and an aqueous expanding vo- lume of 2.5ml/g(dry resin). Stock solution of each rare earth(H)was prepared by dissolving an accurate amount of its oxide(purity 99.95%)into hydrochloric acid by careful heating; then evaporating it almost dry,cooling and diluting with water to a definite concentration,when used as the feed to the chromatographic column it was fur- ther diluted to a siitable concentration and adjusted to a definite acidity. Heavy rare earths feed was prepared by dissolving a definite amount of mixed heavy rare earth oxides,which had been prepared from the enriched heavy rare earths mixture in Yuelong Chemical Plant,into hydrochloric acid then treating it as the same as stock solution of pure rare earth(). Extractants,such as HEHCEHP),DMHCMP]and TBP,which were diluted with liquid paraffin to make organic solutions of 0.05mol/l;but the mixture of petroleum sulphoxide and HEHCEHP]was diluted with kerosene to 0.10mol/1 organic solution. Aqueous solutions of 10%sulphosalicylic acid (adjusting pH to 2.9)and 20%hexamethylenetetraamine were prepared by conventional process respecti- vely, 499

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Standard EDTA solution was prepared with the concentration of 0.001mol/l and then standardized with a standard Zn(I)solution, 1,2 Column Packing At first,the HEHCEHP]resinshould be completely soaked and continuously stirred in 1:1 hydrochloric acid,then the paste-like resin was set overnight. A column filled with 1:1 hydrochloric acid was prepared for column packing. As the hydrochloric acid was dropping slowly form the column outset,the paste-like resin was slowly run into this column while being contiuously stirr- ing.Let the resin settle down by itself to ofrm a resin bed.When the upper layer of the bed had reached the same level as hydrochloric acid,the outset stopper was turned off and a little glass cotten was put and lightly pressed on the bed surface.A definite ml of 1:1 hydrochloric acid was added into this column and the interstitial volume of the resin bed,V,was measured from the formula,V.=V:-V,,where y.and V,are the total ml of hydro- chloric acid being added and the ml of hydrochloric acid flowing out respecti- vely.Take care that the resin bed must not be left dry otherwise many small gas bubbles existing in the bed would reduce the column efficency. 1.3 Conditional Tests for the.Extraction Chromatographic Separation In order to more accurate data,three columns (inner diameter of 16,16 and 11 mm respectively)with the resin bed height of 250,520 and 700 mm respectively were used for conditional tests.At first,the resin bed was tho- roughly eluted with 1:1 hydrochloric acid until no Fe(I)in the solution was flowing out;then it was eluted with 0.1mol/1 HCI until the eluate from the outset was just as much as the same 0.1mol/1.An accurate volume of rare earth feed(pH 2-3)was transferred into the column and let to flow out from the column outset to a container,When the feed had flowed down just to the upper surface of the resin bed,the bed was eluted with dilute hydrochlric acid of a definite concentration as eluent.The eluate was collected at the interval of 5.00 or 10.00 ml into an Erlenmeyer flask,After the addition of 5ml of sulphosalicylic acid solution and 10ml of hexamethylenetetramine so- lution,the concentration of rare earth in each interval was titrated with stan- dard EDTA solution. 2 Results and Discussions 2.1 Kind of Extractants From the data shown in Table 1,it is known that the effect of HEHCEHP] 500

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is better than that of tributyl phosphate(TBP),di-1-methylheptyl methylpho- sphonate(P-350)or the mixture of HEHCEHP]and petroleum sulphoxide,but slightly inferior to that of mixture of HEHCEHP)and TBP.On account of the convenience for the synthesis of resin,we prefer to use HEH[EHP]alone rather than the mixture of HEHCEHP]and TBP. Table 1 The separation coefficients(Lu/Yb)with some extractants Mixture of Mixture of HEH Extractant HEHCEHP] TBP DMHCMP)HEHCEHP]CEHPJand petrol- (P-350) and TBP(vol.eum sulphoxide ratio=4:1) (vol.ratio =1:3) Lu/Yb 1.71 1/1.10 1/1.05 1.78 1/1.23 Conditions aq.phase: aq.phase: aq.phase: aq.phase aq.phase:HNO,(0.3 1mol/1 HCI 3mol/I HCI 3mol/I HCI imol/1 HCI mol/1 NH,NO3 (2.0 mol/1 2.2 Optimum Conditions for the Separation of Yb and Lu Many factors affecting the performance of extraction chromatography must be taken into consideration.The performance or degree of separation actually achieved by each of trials is judged by its resolution power(Rs)which is de- fined as,=(y,-V)l}(W1+形，，where theV,andr:are the retention volume of two neighbouring rare earths and Wi and W2 are the width of the base of eluting peaks of these two,Since the separation of Yb from its for- mer neighbour,thulium,must be considered,the conditions for the separation Elute with 2.0mol/1'HC1 -Elute with 1.5mol/]HCI Elute with 1.0mol/i HCl X)2 10 12 E1uate(×104)/ml A- Fig.1 Effects of acidity RE2O3 are all 10.0mg;=50C;flow ratc=1ml/min.cm2;resin bed,=16mm,L=520mm, 501

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of Tm,Yb and Lu are studied, 2.2.1 Acidity In extraction chromatography,the eluent is generally a dilute acid and most frequently hydrochloric acid.The laboratory data for the effects of aci- dity are shown in Table 2 and Fig.1.Obviously,the higher the acidity of eluent,the smaller the tota!eluent volume required and consequently also the retention volume(V).Hence less time would be consumed and also smaller R. would be obtained.As the eluent acidity is reduced the separation will be improved but more time would be required and larger eluate volume must be handled. Table 2 Effects of eluent acidity on the resolution power Eluent:HCI(mol/i) Dia Dyb Dtu Rs (YbITm) Rs (LuIYb) 3.0 2.52 4.56 7.28 0.64 0.53 2.5 3.20 7.96 12.00 0.98 0.55 2.0 5.92 14.80 26.30 1.09 0.84 D=Distribution ratio of extraction chromatography =(VR-Vi)/Vs,where VR,V:and Vs show the eluent volume with maximum rare earth concentra- tion,interstitial volume of resin bed and volume of stationary phase respecti- vely.c3) (resin bed:=16mm,1=250mm;other conditions are all same as Fig.1.) 2.2.2 Column Loading From Fig.2,it has been known that for the same column geometry,the larger the amount of rare earth loaded on the top of the column,the greater the height of the eluting peak and the more the space necessary for its adsor- ption and consequently the less the space available for its separation;so that the Rs value would be reduced. 2.2.3 Effects of Salting-out Agent The addition of ammonium chloride as a salting agent to the eluent has been proved helpful in giving higher and narrower elution peaks as well as in reducing retention volumes and elution cycle time.But it must be pointed out that ammonium chloride really does not improve the degree of separation. The experimental data are shown in Fig.3.In consideration of both Rs value and time-saving,we prefer to expand the column volume rather than to add salting-out agent in the actual operation for economical estimation. 2.2.4 Effects of Column Geometry Fig.4 shows that the smaller the ratio of column L,the more ideal the 502

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Other RC Column loading: Mixed heavy rare earth oxide -300ng 200mg 3 -100mg- Other RE % 2 Other RE 1 Lu … 2 6 10 12 E1uate(×104)/m1 Fig.2.Effects of column loading =16mm(column inner diameter),resin bed keight=520mm elueat=HCI(1,0ml/1): tcmP.=50℃， flow ratc=1,0ml/min cm2; 36 30 Fig.3.Effects of Salting-out agent resin bed:6=16mm,L=520mm 24 flow rate=1.0ml/min.cm2; 18 t=50℃，Tm203+Yb203+Lu203 =(10.0+10.0+10.0)mg. 12 eluted with 2.0mol/1 HCI; cluted with a mixture of HCI (2.0mo1/1)and NH4CI(3.0moI/1) 100200300400500 Eluate /ml Rs value achievable.For the actual operation,if the requirement for the } degree of separation has been satisfactory,the column length should be as small as possible to save time and reduce eluate volume. 2.3 Mechanism of Extraction Chromatography After the distribution ratios of Yb and Lu (Dxp and DLu)from resin bed by the elution of dilute hydrohloric acids with different acidities were deter- mined,the log D was plotted against pH.A series of straight lines with the slope of 3.1 (~3)indicated that 3H+had been liberated during the extraction chromatography.Hence the mechanism should be the same as in their extrac- tion in a single stage. 503

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24 Column geometry: =16nm,L-250am- -◆上-16ma,L=520mm -◆=11mm,Z=700m 20 Tm- 16 Tm 12 2 2 Eluate(x103 )/ml 200 400 600 800 Eluate/ml Fig.4 Effect of column geometry Fig.5 Separation of Yb and Lu from feed Tm203+Yb203+Lu203 mixed heavy rare carth oxides =(10+10+10)mg影 column loading:50mg of mixed RE2O3 cluent mixture of HCI(2.0mol/l)and colum geometry :=16mm,L=520mm; NH4C1(2.0mo1/l):t=50℃. eluent:1.3mol/I HCI f1 ow rate:1.0ml/min-cm2,t=50℃， 3 Laboratory-scale Preparation of Yb2O3 and Lu203 The higher the acidity,the lower the degree of separation and the less the operating time consumed;on the other hand,the lower the acidity,the higher the degree of separation and the more the operating time needed;so that an optimum acidity for both of the feed and the eluent must be taken into acc- ount.Form various trials,it was found that after a feed,which had been prepared by dissolving 50.0mg of mixed heavy rare earth oxides in dilute hydrochloric acid and adjusting its acidity to 1.3 mol/l,was transferred into a column (=16mm,L=520mm),the loaded rare earths were eluted with 1.3 mol/1 of hydrochloric acid as eluent;there appeared not only a wide blank region between the elution peaks of Yb and other ligher rare earths but also a blank of 150ml between those of Yb and Lu (Fig.5).If the column loading was increased,the acidity of the eluent must be reduced'to guaranttee their 504

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clear-cut separations. In the laboratory-scale preparation,1,0mol/1 of hydrochloric acid was cho- sen to be used as eluent,thus the column loaded with 200mg of mixed heavy rare earth oxides could satisfactorily used for the separation and purification of Yb and Lu,The eluates of Yb and Lu were collected respectively and Yb2O,and Lu2O,were obtained by precipitation with oxalic acid and subse- quent ignition.Their recoveries and purities were determined by EDTA titra- tion and ICP respectively.The determined'values are listed in Table 3.After 50 cycles of extraction chromatographic operation,1.96g of Yb2O,and 5.69g of Lu,O3 were obtained. A program of expanding the test for the commercial production of Yb2O3 and Lu2O,has been put forward,The use of a larger column with an inner diameter of 52cm and a resin bed height of 17m is under consideration(for the loading of 200g of mixed heavy rare earth oxides). Table 3 Recoveries and purities of Yb2O3 and Lu2O3 (n=6) Yb2O3 Lu203 Raw material(determined by XRF) 20% 60% Recovery 99% 95% Purity 99.95% 99.90% 4 Conclusion (1)Clear-cut separation of Yb and Lu by extraction chromatography using HEHCEHP]resin has been proved to be applicable for the preparation of pure Yb2O,and Lu2Os on laboratory scale. (2)From actual experimental data and in the practical consideration of time required and degree of separation required,the recommended operating conditions for the separation of Yb and Lu are listed as follows: Column Geometry:Diameter=16mm,resin bed height=520mm. Column loading:Mixed heavy rare earth oxides 200mg. Eluent:1.0mol/I hydrochloric acid. Flow rate of eluent:1.0ml/min.cm2. Salting-out agent:Unnecessary. Temperature:50C. (3)Blank eluate in between Yb and Lu clution peaks has been proved to be no less than 150ml. 505

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(4)Yb2O,and Lu2O;obtained; Purities;99.95%(Yb2O3);99.90%(LuaO,) Recoveries:99%(Yb2O3);95%(Lu2O3). References 1 Hu Renkun,ct al.Analytical Lab,1986,5(1):60 2 Shen Fengyun,Fan Limin,et al.Rare Metals,1991,10(1):55 3 Sun Suyuan,et al.Extraction Chromatography and Its Application,Ato- mic Engergy press,Beijing,1982 506

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