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Jou rna l of Radioanalyt ical at td Nu clea r Chemistr3; Art ic les, ! /ol . 162 , No. 1 (1992) 4 7-56

EXTRACTION SEPARATION OF RARE-EARTH ELEMENTSBY AMINES IN THE PRESENCE OF COMPLEXING AGENTS

II. SEPARATION OF Ce AND Y IN THE PRESENCEOF ETHYLENEDIAMINETETRAACETIC ACID

J . K O V A L A N C I K , * M . G A L O V A * *. . vL abora toIT for Ra re M e ta l s C hemis tl3 ; S lovak Academy o fSc ien ces , 043 85 Kogice (CSFR)

**Department o f Chem lstry , F acu l ty of M etal lurgy, Techn ical Universi ty , 043 85 Kogice (CSFR)

( Rece ived Se ptem ber 2 , 19911)

T h e e x t r a c l io n s e p a r a t i o n o f C e a n d Y b y b e n z y l d i b u t y l a m i n e ( B D B A ) in t h e p r e s e n c e o fe t h y l e n e d i a m i n e t e m l a c e t i c a c id ( E D T A ) a s c o m p l e x i n g a g e n t h a s b e e n i n v e st i g a te d . T h e s e p a r a ti o nf ac tor s CtCe /Y . in abse nce of co mp lexi ng agent r anging f r om 2 0 - 4 0 , inc r ease a t p r oper ED TAc o n c e n t r a t i o n s b y 1 - 2 o r d e r s o f m a g n i t u d e . T h e s e p a r a t io n o f Y a s m i n o r o r e v e n t ra c e e l e m e n t f r o mthe m ajor C e i s so e f f ic ien t tha t i t s concent r a t ion in the or ganic phase l i e s be low th e de tec t ion t imi l o ft h e a n a l y ti c a l m e t h o d .

Introduct ion

In the previous paper o f this series I it was demonstrated that the extraction separationof rare earth elements (REE) by amines is not very efficient but may remarkably beimproved by addition of a proper complexing agent into the aqueous phase. The valueof separation factor aL.~,Sm increased 7-10-fold in the presence of 2-hydroxyethyl-ethylenediaminetriacetic acid (HEDTA). The procedure described enabled very goodseparation of major (La) from minor (Sin) elements, provided that the stability constantof the minor element is sufficiently higher than that of the major element and thus, theminor element is kept in the aqueous phase. On the other hand, preferential extraction ofthe major element must occur. In case of REE extraction by amines, the lighter elementsLa, Ce, etc., representing in most natural ore samples the major REE, are extracted beforethe heavier ones.

Therefore, the choice of the suitable complexing agent is based on the stabilityconstants of the complexing agent with the individual REE. The present work is aimedat the separation of Ce as a major element from Y as a minor or even trace element. Thestability constants of various complexing agents and their difference for both elementsstudied are summarized in Table 1. Two complexing agents, 1,2-diaminocyclohexane-

Elsev ie r Sequoia S . A . , LausanneAkaddm lal Kia,bS, Budapest


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J . K O V A L A N C I K , M . G A L O V A : E X T R A C T I O N S E P A RA T I O N , 11.

te t raaeet ic acid (D CI 'A ) and ED TA sh ow the greates t d if ference as to Ce and Y com plexformation. Th e latter one, D CT A, p roved to be unsuitable du e to its low solubility inacid ic so lu t ions , as the aqueo us phase in case of amine ex traction is 0 .5 m ol . dm -3 HNO3"

T a b l e 1S t a b i li t y c ons t a n t s o f va r i ous c ompl e x i ug a ge n t s w i t h C e a nd y 2Com plexiug age nt log 1SEe log [~y Di f fe rence

DC TA 16.76 19.15 2 .39ED TA 15.98 18.10 2 .12EG TA 15.70 17.60 1 .46HE DT A 14.20 14.65 0 .45PD TA 16.80 18.76 1 .98

N o ~ :D C T A -E D T AE G T A -H E D T A -P D T A

1,2-diamiuocyc iohexane te t raace t i c ac id .e thylenedinmine te t raace i c ac id .e thyleueglycol -b i s (2-a miuo e thyle ther ) t e t raace t i c ac id .2 - hyd r oxye l hy l c t hy l e ue d i amine t r i aee t i c ac id .pm phy leuediamiuc te t raacef ie ac id .

The ED TA me ets the requirements bo th as to the s tab i l ity constan t d if ference for Ce andY and to the solubility in the aqueous phase; therefore, i t was chosen for furtherexper iments .

ExperimentalReagents

Ce(NO3)3 , Y(NO3)3 (V entron , Germ any) , benzene, NaN O~ , HN O 3 (Lachema,Czech oslovakia) were reagents o f analy t ical g rade. BD BA was prepared in the ResearchInstitute for C hem ica l Te chn olo gy, Bratislava (Czechoslovakia), in 99.8% purity.

The so lu t ion of 14ICe ( in the form of C eCI3, Am ersham, England), M y (in the formo f Y C I3 , Tekhnosnabe kspor t , U SSR ) was used .

Apparatus an dproceduresThe ra dioactivity wa s mea sured by a scintillation probe NZ -420 provided with a

NaI(T1) we ll- type detecto r in conn ection with a single-channel analyzer NP-42 0 (ME V,Hungary). The radionuclide purity of the original prelmmtions was checked by ascin t i l la t ion spectrometer Robotron 20 050 (Germany) . A d ig i ta l pH meter typeOP-250/1 (Radelk is , H ungary) connected to a com bined g lass e lectrode was used .48


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J . K O V A L A N C I K , M . G A L O V A : E X T R A C T I O N S E P A R A T I O N , I I.

Th e c o u n t s w e re re a d f ro m two s l i c e s o l th e ,./ -s pe ct ru m o f th e ra d io n u c l id e mix tu re .Co u n t in g s o f th e s a m p le s c o n ta in in g e i th e r r a d io c e riu m o r r a d io y t t riu m we re m e a s u re dw i t h i n t h e s l i c e s a t t h e b e g i n n i n g o f t h e e x p e r i m e n t . T h e r e p r e s e n t a t i o n o f t h era d io n u c l id e s in th e mix tu re wa s th e n d e te rmin e d b y c o mp a r i s o n o f th e se me a s u re me n ts .O th e r e x p e r ime n ta l d e ta i l s we re th e s a m e a s d e s c r ib e d in Re fe re n c e 1 . ,

S ta t i s ti c a l d e v ia t io n o f th e a n a ly t i c a l me th o d w a s l e s s th a n 1 %.Co mp o s i t io n o f th e a q u e o u s p lms e:

CONaNO~--- 6 tool- dm-3, COHNo3 - 0.5 mol- dm 3

C0y(NOg~ = 5" 10 4, l 9 10-3, 5- 10 3 tool- dm-3

0CefNO.9.~ 5 9 10-4 , 5" 10 2 nlol. dm 3 so that

C~176 -- i:i, 1:2, 1:5, i: i0, 1:20, 1:50, I: i00

C 0 E D T A = 0 1 " 1 0 2 m o t . d m -3 s o th a tC0 . V(NOg~,C0EOTA-- 1:0 , 2: 1, 1:1 , 1:2

C o m p o s i t i o n o f t h e o r g a n i c p h a s eC0BDBA-- 0 .5 , 0 .75 , 1 .0 m ol . dm -3 in benzene .

R e s u l t s a n d d i s c u s s i o n

Figu res 1 , 3 , 5 and 7 s how the dep end ence of d is t r ibu t ion ra t ios Dy, Dec and F igs 2 ,4 , 6 , 8 those o f separa t ion fac tors c tc~/s upon the add i t ion of com plex ing agen t , ED TA ,a d d e d to th e a q u e o u s p h a s e , a t v a r io u s e x t rac ta n t a n d B DB A c o n c e n t ra t io n in th e o r -gan ic phase . Th e exce ss o f Cc~ ov er c , inc reases f rom 1-1 in F igs 1 , 2 th rough 5-fo ld inFigs 3 , 4 , to 20-fo ld in F igs 5 , 6 to 100-fo ld in F igs 7 , 8 . The pre fe ren t ia l ex t rac t ion ofCe e x p re s e d b y h ig h e r Dc ~ a s c o mp a re d wi th Dy v a lu e s i s c l e a r ly s e e n in a l l c a s e spresen ted in F igs 1 , 3 , 5 , 7 . T he sam e is t rue fo r the decrease in D e v a lues wi th increas -in g c o n c e n t ra t io n o f EDT A. A t a two - fo ld e x c e ss c o n c e n t rat io n o f ED TA o v e r Y i t sconcen tra t ion in the o rgan ic phase f luc tua tes a round a t the de tec t ion limi t o f the ana ly-t ica l m etho d used , w hich resu l ts in ver y low d is t r ibu t ion ra t io (Dy) va lues.

Th e d i s t r ib u t io n ra t io o fC e , Dc e, d e p e n d s , e v id e n t ly , o n th e ra tio o f in it i al Ce to ED TAc o n c e n t ra t io n s in th e a q u e o u s p h a s e . Th e mo s t r e ma rk a b le c h a n g e s o f Dc ~ wi th th e

4 9


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J . KOVA LAN C I K, M . GA LOV A: EXTR A C TI ON S EP AR ATION, 11.d 3 ' L 6

IP

d ~ O m 2

Q : 110 11 12 "v

9 0

Fig. 1. Dependen ce of the dislributiou ratios D y (curves 1, 2, 3) and DCe (curves 4, 5, 6) upon the addition ofcom plex ing agent (ED TA ) to the aqueous phase. ]nil ia l aqueous phase composition: 6M NaNO g, 0 .SMHN O-. c O . . . . 10-3M, r . . . . + IO-3M, in it ia l organic phase composi tion: cO n, - ~- 0 . SM(curves 1, 4), 0.75M (curves 2, 5), IM (carves 3, 6)

100 3

0 ~-1 : 0 1 : 0 5 1:1C ~ y ( N O ~ ) 3 :E D T AFig. 2. Dependence of the seDara t ion factors (tCe/Y uplx~n the addition of complexing agent (EDT A) to th e

a~ueous phase. Init ia l aqueous ph ase composition: 6M N aNO 3. 0.5M HNO3, cg,(NO})~ = 10 -JM ,c~.,.(NO~)~ - IO-3 M initial organ c phas e comp osition : CODBA = 0.5M (carve 1) 0.75M (cu~,e 2). IM50 (curve 3)


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J . KOVALANCIK,M. GA LOVA : EXTRAC I 'IONSEPARATION, ILc o m p l e x i n g a g e n t c o n c e n t r a t i o n o c c u r i n t h e r a n g e w h e r e b o t h C e a n d E D T Aconc ent rat ions are com parab le , i .e . under condi t ions descr ibed by Fig . 1 and perhaps Fig .3 . The C e( [ [I ) i ons here a re bound in t he ED TA complex and thus, i n the aqueous phase ,and the d i s t ri bu t ion r a tio decreases . Wi th increas ing excess o f Ce over E DT A the va lue

d6

t 5 -

1.0

Fig. 3. Dep endence f t h e distribution atios D y (curves l , 2, 3) a n d D ~ (curves4, 5, 6) u pon the addition feomplexi~g agent (EDT A!;o t h e ~ q n e o n s p h a s e . ,n i _ ti~ ,a q u e o u s p h a s e composition:6 M N aN()0~,0.5MHNO 3, cO(NOah ,, 5" tO- M, c ~N O.~)~" 2.5. i0 - M, initial organicpllase eom posltioa:CBDBA= 0 . S M ( : , .. e , ,r 4 ) , 0 7 5 M ( c u r v 2 , 3 ' 6 )

of Dcr l o ses i ts depend ence on the ED TA concen t ra tion va lue as can be seen in F ig . 5,corresp onding to a 10--20-fold ex cess . Ap proxim ately at 50-fo ld excess of Ce ove r EDTAconcen t ra t ion , Dc~ becom es co ns t an t ( see F ig . 7 ) . T he va lues o f e i ther D y o r Dc~ showtha t t he ex t r ac tion o f t hese R EE by B DB A i s no t very e f fi c ien t .

The separat ion process , on the o ther hand , i s represen ted even in the absence ofcom plex ing agen t by r va lues r ang ing f rom 20 to 40 . The add i ti on o f ED TA leads toan increase in c ~ r t va lues by 1 -2 o rder s o f magn i tude wi th the excep t ion o f very h igh(100-fo ld) excess of Ce o ver Y presen ted in F ig . 8 , wh ere the increase in ~-c ~ values : son ly 2-fo ld . This fa l l i s caused by the remarkable decrease in the Dc~ values wi th

51


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J. KOVAL ANC IK, M. OALO VA: EX'I'R&C-TI.0NS F 2 , A ~ T I O N I L

i n c r e a s in g i n i t i ~ ~ c o n c e n t r a t i o n i n t h e a q u e o u s p h a s e o v ~ r a g i v e n v a l u e . T h e e f f e c t i ss h o w n a l s o i n F i g , 9 , w h e r e t h e d e p e n d e n c e o f D y , D e c a n d c q~ ,~ , o n i n c r e a s in g C e ( l ! l )c o n c e n t r a t i o n i s p r e s e n t e d . A t l o w i n i ti a l c o n c e n t r a t i o n o f C r t h e D e e v a l u e i si n d e p e n d e n t o f C c~ a n d s t a r ts t o d e c r e a s e o n l y a t h ig h e r c cr c o n c e n t r at i o n s , a b o v e 1 0 2

A

1 _I . ' 0 1 : 0 . 5 1 : 1 1 : 2 -~(,,~:C~

Fig. 4. Dependence of the separation faeto~ o ~e m Upon the addition O[ com plexilg agent (EDTA) to Ihe9 . t ~ . . . . . . . . 0 -a ueous phase, huf ial aqueous phase com l~stl ion: 6M NaNO 0.SM HNO3, e - 5 - l 0 3 M ,] ' " . . . . . . . . . . ' " . . . . " ... o 3 ' . . . . . y / ( N o j ) 3 ,e ~ N O ~ ) ~ - 2.5" 10- '~M, nitia l or ph ic phase composition: CBDBA= 0.5M (curve !) , 0.75M (curve 2) ,1~1 (cnr~ e3) " . . . . "

t o o l . d rn - 3. T h i s e f f e c t m a y b e e x p l a i n e d a s f o l l o w s : t h e e x t r a c t io n p r o c e e d s - i na g r e e m e n t w i th o u r p r e v io u s r e s u l t s 1 ,3 - ae c ~, rd in g t o th e e q u a t i o n :C e 3+ + 3 N O ~ + 2 B D B A 9 : IN 0 3 - { C e (N 0 3} ~:-" ( B D ~ * ) 2 } ( 1 )

T h e p r e s e n c e o f E D T A i s n e g l e c te d h e r e s in c e o n l y f re e C e 3+ io n s t a k e p a r t i n t h ee x t r a c t io n p r o c e s s . T h e e q u i l i b r iu m c o n s t a n t o f r e a c ti o n (1 ) , t h e e x t r u s i o n ~ s t ~ n t K e x,m a y b e e x p r e s s e d a s f o ll o w s :

K~,, t = [ { Ce(NO 3).~-(BDB AH *)2} ]{Ce3+] 9 N O ~ ] 3 " [ B D B A 9H N O 3 ] 2

(2 )

5 2


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J . K O V A L A N C I K , M . G A L O V A : E X T R A C T I O N S E P A R A T I O N . I! .

2 0Q

1.5

10

d o o ~ .

o o ~

6

5

" n

m

0. V ( N 0 3 ) 3 : C sF ig . 5 . Depen denceof the d is t r ibu t i on ra t ios D y (cur ,,es 1 , 2 , 3) and DCe (curves 4 , 5 , 6) gpo n !he add i t ion o f

c o m p l c x i n g a g e n t ( E D T A ) t o t h e a q u g o u s p h a s e . In i t ia l a q u e o u s p h a s e c o m p o s i t io n : 6 M N a N O 3 , 0 5 MH N O 3 ' C O i N . ( ~ I I ' 1 6"~ 3M " r ' 2 " 1 0= 2M , i n it ia l o r s a n ic p h a s e c o m p o s i ti o n : e ~ ' 0 . 5 M( curves 1 , 4 ) , 0 . 7 5 M ( c u ' c s 2 ' , " 5 ) , 1~ i cu r ves 9 6) ~ " -

T a b l e 2S e p a r a t io n f a c t o r c t c e /y o b ! a i a e d i n t h e a b s e n c e a n d p r e s e n ce o f c o m p l e x j n g

a g e n t E D T A a n d i n c r e a s i n g C e ( N O 3 ) 3 c o n c e n t ra l io n ; a q u e o u s p h a s e1 " I O~ 3 m o i : d m - 3 y ( N O 3 ) ' ~ 6 t o o l . d m - 3 N a n O 3 , 0 .5 m o l . d m - 3 H N O 3 ;

o r g a n i c p h a s e : 1 .0 t o o l - d m - 3 B D B A i n b e n z e n e

C o n c e n t r a t i o nO f C e 3 ' ,

m o l - d m - 3

u t t e / YCOy : " . COEIYrA

1 : 0 2 : 1 1 : 1 1 : 21 , 1 0 3 2 5 4 6 2 0 5 *2 " 1 0 3 2 4 4 5 1 4 5 3 3 2 05 " 1 0 3 2 4 4 5 1 0 4 6 0 0I 9 1 0 2 2 6 4 3 7 8 5 3 42 " 1 0 2 3 0 4 1 7 1 2 0 65 " 1 0 2 3 3 5 8 6 0 2 1 2I 9 1 0 - 1 3 3 3 9 4 2 5 8

* c ~ , v a l u e s a r e b e l o w t h e d e t e c t i o n l i m i t o f t h e a n a l y t i c a ls e q u e n t ly , n e i t h e r D y n o r C tC e / Y v a l u e s c a n b e d e t e r m i n e d . m e t h o d a n d , c o n -

5 3


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J . K O V A L A N C I K , M . G A I / ) V A : E X T R A C T IO N S E P A R A T I O N , I f .

B

20O

10 0

] '05 ] : 1 1 2. . C v ~ , , o , > i C ~ , ,

Fig. 6. Dependence of the separat ion, fac lors (zCc/y upon the addi t ion of eom plex ing agent (EDT A) to theuqueotl s phase . In i l i a l aqueou s phase com posi t ion : 6M Ha l lO3 , 0 .5 M H N O 3 , c O , , ,O . - l O - 3 M ,0 . . . . . . . 0 I LL~_ ~ ] 3 .C_Cr " 2 " l0 2M, ini t ia l orga nic phase composi t ion: eBDI3A - 0 .SM (curve I . ), 0 .75M (cur ve 2) ,I M ( c u rv e 3 ) L

c ~ 1 . 2 5 -

6LC

_ 5

.t 9

d ,~ O O S O

0 I ] i _1 : 0 2 : 1 1 :1 1 : 29 0~ C N O ~ ) ~ . C E D , A

F i g . 7 . l k p e n d e n c e o f t h e d i s tr i b u ti o n ra t i o s D y ( c u r v e s 1, 2 , 3 ) a r id DCe (curves 4 , 5 , 6 ) u p n the addi tion ofc o m p l e x i n g a g e n t ( E D T A ) t o the aqueous p h a ~ , In it ia l aqueous pha .~ com posi t ion : 6M NaNO~, 0 .5MHNO 3, cOfNo,~ , - 5 . IO"~M, c~ N O )) ; - 5 - 10-2M, in it ia l o rganic phase composi tion : c O B A~- O.S M

5 4 (curves 1 , ~ ) , 6 . '; /5M (curves 2 , 5 )~ M ' (curves 3 , 6 )


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J . K O V A L A N C I K , M . G A L O V A : E X T R A C T I O N S E P A R A T I O N , 11.

T h e d i st r ib u t i o n r a t io D c e - a s s u m i n g h e r e t h a t c o m p l e x fo r m a t i o n c a n b e n e g l e c t e d- i s t h e r a ti o o f C e e q u i l i b r iu m c o n c e n t r a t i o n in t h e o r g a n i c a n d a q u e o u s p h a s e s :

O c ~ = H C e ( N O 3 ) ~ " ( B D B A H * )2 } ][Ce3+] = ] (, ex t" [NO:~] " [E D B A . HNO 312 (3 )

23

5O

4O

1:0 1:0.5 1:1 0C v ( ~ : ) 3 1 " C E O r AF i g . 8. D e p e n d e n c e o f t h e s e p a r a ti o n f a c t o r s t tY / Ce u p o n t h e a d d it i o n o f c o m p l e x i n g a g e n t ( E D T A ) t o t h e

a o u e o e s p h a s e . I n i ti a l a q u e o u s p h a s e c o m p o s i t i o n : 6 M N a N O , 0 . 5 M H N O ~ c f f . . . . . 5 9 IO-4M,c C~NO.~)~ - 5 " IO-~M, in i l i a l o rgan ic phase com pos i l ion : eBD B A - 0 . S M (ca lve 11 , 0 . 75M (curve 2 ) ,IM (cei~,e )

I n a c c o r d a n c e w i t h E q . ( 1 ), t h e e q u i l ib r i u m c o n c e n t r a ti o n o f t h e e x t r ac t a n t m a y b ee x p r e s e d i n t h e f o r m :

[ B D B A 9H N O 3] = C0BDBA 2oce ( 4 )I n s e r t i n g E q . ( 4 ) i n t o E q . ( 3 ) , t h e f o l l o w i n g e x p r e s s i o n i s o b t a i n e d f o r D c ~

Dc~ = Kex 9 [NO~] 3 9 [C0BDBA - 2C ~ ( 5 )e x p l a i n g t h e c h a n g e i n D ~ v a l u e s w i t h i n c r e a s i n g c ~ : ( c u r v e 2 , F i g . 9 ). F o r l o w c ~ v a l u e swhere C0BOnA> > c o t , t h e c h a n g e o f t h e th i rd t e r m i n E q . (9 ) m a y b e n e g l e c t e d a n d D &

5 5


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J. KOVALA NCIK, M. GALOVA : EX TRAC TION SEPARA TION, 11,

1.5 100

d 0050~ ~ 500 .0 2 5

O | L I I- 3 - 2 - 1otog Cc,(No3)3Fig. 9. Depend ence of the distribution ratios D y (curve 1), DCe (curve 2) an d separation factors r (curve

3), upon the log concentration of Ce(NO 3)3 in exlraci ion w ilh 1M BD BAappe ars inde pen den t o f Cc~. W ith incre asing c ~ valu es both C~ and COc~ onc entra t ionmus t be t aken in to acc oun t , wh ich i s r e f lec t ed in t he decrease o f Dce in acco rdance w i thequa t ion (9) a nd , co nseq uent ly , a l so in the dec rease o f e tc~rv (see curve 3 , F ig . 9 ) .

The mos t r emarkab le e f f e c t o f i nc reas ing acc /v in t he p resence o f com plex ing agen tE D T A i s d e m o n s t ra t e d in T a b l e 2 .

The r esu l ts p resen ted here con f i rm tha t a ca re fu l ly chosen com plex ing agen t andconcen t ra t ion may enhance the separa t ion e f fec t i n ex t r ac t ion separa t ion o f REE byamines . S imi l a r ly as i n t he p rev ious work 1concern ing separa t ion o f La as a m ajo r e lemen tf rom Sm as a m ino r e l emen t i n t he p resence o f HEDTA , a l so in the p resen t work thesepara tion o f excess C e over Y has been improved by add it i on o f EDT A due to bo thp re fe ren ti a l ex t r ac t ion o f l i gh t REE as L a and Ce b y amines and p re fe rent i a l comp lexfo rmat ion o f t he o ther i on S in , Y b y the com plex ing agen t chosen .

Reference s1. J . KOVA LANC IK, M . GALOV A, J. R adioanal . Nucl. Chem., 162 (1992)35.2; J. INCZ]~DY ,Analyt ica lApp lications o f Com plex Eq uilibria, Akad~ miai Kiad6, Budapest, 1976.3. Report on the Research Project , No. I I I - 1-7/05, Study of the Physico - Chemical Condit ions of REEIsolation and Chem om etric D etermination, Kosice, 1989 .5 6

fulltext(complexing agents)

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