A vai l a bl e onl i ne at w w w．s ci ence di re ct．com
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：，Sci enceD i rect
J O U R N A L O F R A R E EA R T H S,V oL27,N o．5，O c t2009,p．830
腿E翩S
Separ at i on of m i ddl e r ar e e ar t hs by sol ve nt ext r act i on usi ng
2-et hyl hexyl phos phoni c ac i d m ono-2et hyl hexyl es t er as an e xt r a c t a nt
D ani l o Font ana，L or i s Pi et r el l i
(F2V FA,I t al i anN at i o nal A gencyf or N ew Technol ogi es,Ener gyan dt heEnvi r onm ent V i aA ngui l l ar ese301，1-00123R om a,t缸t y)
R eceived9Fe b r uar y2009；诧、，i sed21M ay2009
A bs t r ac t：The ext r act i on of t he t ri valent m i ddl e nI re ear ths f r o m chl or i de m edi a by ke r osen e s ol ut i ons of
2-et h yl h exy l pho sph oni c aci d m on o-2。e t hyl he xyl
est er勰a l l ext r a ct ant w as s t udi e d．T he s epar at i on f act or s bet w e en t he el e m en t s us i ng s ol u t i on si m ul at i ng W asPS f r om
N i M H sp ent bat ter i es ha ve be e n eval uat ed：t he or der of nl c ext r act i ve a b i l it y of ext r a ct ant
c a n be conf i r m e
d i n T b>G d>E u>Sm．
K e yw or ds：sol ve nt extr act i o n；nIr e ear t h s；s epar at i on
R are ear t hs f R E)el em ent s ar e a gr oup of15e l e m ent s (at om i c num b er s57—71)havi ng t hei r st r i ki ng l y si m i l ar chem i cal pr ope r t i e s a nd t he y ar e c onve nt i ona l l y di vi de d i nt o
3gr oups：t he l i ght(h C e，耽N d)，m i ddl e(S m，Eu，G d，Th) andhe avy(D yt oLm．
T he R E e l e m ent s occ u r t oget he r i n l l aR l r e i n so m e m i l l er-
als l i ke bas t na si t e，m ona zi t e，xenot i m e and ot her s；t hes e
m et al i on s have been used f or addi t i ve s t o st eel s o r all oys，per m anent m agnet s，hydr ogen st or age m ater ial s，m ag—ne t o-opt i c st or age di scs，el ect r o o r cat hode r ay l um i nes cence。hou s eho l d bat t eri es．et c．11川。t heref or e i n addi t i on t o t he pri．
m ar v source s s uch as t he com m er ci al．enr i ched or es of t he abo ve re ferre d m i ner al s．w as t e s s uch as s pent cat al ys t s．su-per-aU o y sc r ap，spen t bat t e r i es，sl udge，dus t s，et c．al e pot en—ti al s ec onda ry sour ce s of r a r e ear t hs．
Som e aut hor sI j l obt ai ned a m i xed r ar e ear t h oxi de product f r om N蝴H spe nt bat t e r i es cont ai ni ng l an廿l anum,cer i um and m i ddl e r a r e eal't hs o f devel oped a hydrom et a l l ur gi c al
pr o cess一1t o obt ai n a pr eci p i t at e of m i xed r ar e ear t h f r om t he sa m e t ype of w ast e pr odu ci ng an enr i ched m at er ial．T he c ur r e nt paper ext ended t he w or k t o es t abl i s h t lle l abo．
r a t or y c ondi t i ons f or m i ddl e r a r e ea r t hs se para t i on by s01．vent ext r act i on a nd t o devel op a su i t abl e econ om i cal l y vi．a bl e s epar at i on t ec hni que f or t hi s se para t i on because t hei r va l ue depend s on ef fe ct i ve s epa r at i on i nt o hi gh pur i t y co m pou nds．
Sever al l i qu i d i on exchangers have been used i n or de r t o ext r act m e t al l i c speci e s and t he m os t w i d el y us ed ar e t he
phos phor i c aci d based aU(yl pho s phorus r eage nt s suc h as t he bi s(2一et hyl hexyl)phos phor i c ac i d,t he2-et hyl he xyl 2-e t hyl he xyl phos phoni c aci d(EH E H PA)(al s o know n as 2-e t hyl he xyl phos phoni c ac i d m ono-2一e t hyl hexyl est er (H E H(E H P))and t he bi s(2-e t hyl hexyl)phosphi ni c aci d w hi ch ar e a ppl i ed i n t he se pa r at i on and pur i f i cat i o n of m et al ca t i ons of di f f e r ent val enceI s,6]．
O ut of t he t hr ee t ype s of ext r a ct ant s，t he bi s(2-e t hyl hexyl)
phos phor i c aci d is t he l east sel ect i ve and t he bi s(2-et hyl he xyl)phos phi ni c aci d，t hou曲m ost sel ect i ve，i s t he m os t expens i ve．A s H E H E PA has been s ho w n t o over-
com e s uch pr ob l em s as hi2I l aci di t y r equi red i n ext r ac t i on and st r i ppi ng and em ul si on f or m at i on‘川，i t m ay be t he bes t choi ce．
So m e aut hor s i nves t i gat e d t he se pa r at i on of m i ddl e R E by com b i nat i on of el ecl T ochem i cal re duct i on and sol vent e x．
1m t ion[8--13】．
nl e st ud i es i nvol vi ng m i ddl e R E ext r a ct i on f r om hydr o—
chl or i c aci d m edi a us i ng H E H E P A al e a f ew and U SU a l l y
ca rri ed out at l ow R E conc ent r at i ons(¨g／L t o m e／L)，t hus f ur t he r i nves t i ga t i on concerni ng t he behavi our of t h i s e x．t r ac t i on s ys t em s ov e r a r el at i vel y w i de conc ent r at i on r ange s eem s t o be appr opr i at e．
1E xper i m ent al
A l l r e agent s w er e of ana l yt i c al grade and w er e us ed w i th．
out f ur t he r pur i f i ca t i on；i n pat t i eul ar t he H EH EP A(s uppl i e d by R hodi a)w as used as r ecei ved．
A s sm al l am ount s of di aci d s u ch as2．et hy l hex yl phos．phoni c aci d ar e us ual l y pr es ent i n t his com m er ci al ext r act ant, H E H E P A w as t i t r at ed by a st anda rdi se d sol ut i on of pot as．
C or r espo ndi ng aut h or：
D an i l o Fo nt an a(F-m all：danil o．f on t an a@en ea．i t；TeL：+39-06-3048．3220)
D O h10．1016／S1002-0721(08)60344-0