360

STUDIES ON THE EXTRACTION 01” ZIRCONIUM 1VITH ORGANOPHOSPHORUS COMPOUNDS

I-illC(JICA%U Ij%li<%:\\VA AND It~SINOSUII;IS I-I.-\I<t\*

fupnrr A lo&c E~wvgy Iitaxtvch Iarsliltrle, Toltui, Jlxwulti /.Jttptt~l)

(I~cccivcd January I 7tl1, 1961)

Zirconium is one of the clcmcnts which nrc rcatlily cstractcc! wit11 or~anopl~ospl~orus solvents, and solvent cstrnction with tri-lt-hutyl phosphate, ‘TBP, has !xxn succcss- fully cmploycd for tlic fractional isolation of zirconium from hnfniuml. Altliou~li tlic solvent cstraction tccl~nicluc is alrcncly in plant scale use for the isolation of zirconium, only a few pnpc33 have c!cnlt with the funclamcntal xspccts of zirconium cstraction”-5. The prcscnt stucly was initiated in an attempt to obtain a pattern of zirconium lxlinviour during cstraction wit.11 or~~~nopl~ospl~or~is coml~ouiicls in- clucling nlky! pl~osplx~tes, phosplionate, pl~ospliinatc! and phosphine osiclc, so that a lxttcr sclcction of rcngcnt could lx! maclc for analytical purposes.

%i~w~i.i~f 111. Tlic raclioisotopc “%r was suppliccl by Oak I‘Ciclgc N~ttiona! Lal~oratoq in the osalatc form, which was convcrtcd to nitrate 13~ boiling with nitric acid, and a reagent gratlc %rO(Non)~ was suppliccl by Yokoxawn Chemical Co., Tokyo. Throughout the work (‘%r was scpxratccl from its tlnugl~ta ~I~Nb immcclintcly before uscfi*“. For the rrl;UXOScidC cspcrimcnt, tlic zirconium solution was prcparcd ns follows: after the tracer {Wr was ndcletl to tlic solution of zircon\?1 nitrate, tlic zirconium was prccipitatccl as tlic hyclrosiclc, tlicn clissolvccl in nitrii acid. The nbovc process was rClX2iLtCCl tlircc times in orclcr to mis the (Wr tracer tliorougl~ly with the non-riidio-

iLCtiVC zirconium wrricr.

Ovh’(1,}10~Jr~~~~Jlowrs so,?v~~~k. ‘1’1~0s~ WCI’C : Pl~ospl~atcs - tricthyl, tri-gt-propyl, tri-a-lxityl, tri-iso-butyl, tri-see-butyl, and tricyclohcsyl pl~ospl~ntcs ; l~!~ospl~onatc - clicthy! butyl l~l~osl~lionatc; pliospl~inatc - tri-9t-butyl pl~oslhinntc, iWC1 pl~osplhc osiclc -- tri-9t-!>utyl pliospl~inc osiclc. All the 0rgilll0l~llOsl~!lOr~lS SolVctI tS were syntlwsizccl !>y Tama Clwmical Co., ‘Tokyo, ;mcl purificcl by vacuum tlistillation. ‘I’hc tri-a-butyl pliospliinc osiclc WilS purified 13~ rccr2lstalli;satit,n from lxnzcnc. Tlic stock solutions of tllcsc solvents wcrc) kept in a rcfrigcrxtor to ilvoid clccomposition.

0th~ cJ~cmicds. Nitric ;tcicl ancl cilrbotl tetrnchloridc wcrc of rcagcnt grade, the latter being clistillcc! before use.

ESTI~AC’~~O~ OF Zr. WITH orxxso-P COMPOW s ns 361

The cstraction tvss carricc! out in nitric acid mcclia. Tfxe solvent was diluted wit!1 carbon tetrnchlorido. The zirconium solution and the solvent were mixed in equal volumes in a measuring flask, ant! shaken in a thermostat. After equilibrium Ilad been rexhed, suitable volumes of both the ac!ueous ancl organic phases were taken, and the radioactivity and a~!ucous nitric acid concentration were determined, The solvent was prc-ec!uilibratecl with nitric acid before the estrnction.

‘T!uz radioactivitv af TSr was measured witl’l a gamma scintillation counter, and the nitric acid co;lcentration in the aqueous !~h;& w;\s clctermincd by ordinary titration.

,he ~!istril?~lti~l~ cocffi- ‘L’llc cstraction ability of the solvent is csprosscd in terms of t ciont between aqueous and organic phnses.

An “Infracorcl“ spectrometer with silver chloride cells was infrared spectra.

used to me;ksure tlrc

Estrilction curves of ty!ricn! phosph:ttcs, phasp!~onate, phosp!~inntc nnc! phos- !>hine osicle arc shown in Fig. x. In the cstraction with normal a!!ql p!~osph~itcs and tri-iso-!)utyl !>hosp!l;ttc, the Kd values increase steeply i1H the nitric acid conccntra- tion incmnscs, whcrc;ts in the estrnction with tri-see-buty! pl~osphatc, tricyclohosyl- ~~~~OS~~~~i~t(~, ~?~~osp~loi~;~~~, pllosl~l~in~tt~~ ant! p!~~~!?l~ine oxide the K,i x*a!ties decrc:tse after s!ow!~ renctiing ;k rn;kmum at about s-7 rlf nitric acid. ‘i’!~ cstntction abilit>*

362 H. UMJDAWA, I<. HARA

is affected by the suhstittients in the phosphoryl group as well as by the structure Of the solvent. As fol the phosphates with normal alkyl groups, it was obscrvecl that the cstraction ability increases slightly as the carbon number of the alkyl group

increases. ‘Tl~e estraction ahilitics of normal nlkyl phosphates arc in the following

Order: tri-n-butyl phosphate > tri-a-propyl phosphate =;- triethyl phosphate.

The effect of branching in the alkyl group was csaminccl with tri-iso-hutyl pho.s- pliatc, tri-see-butyl phospllatc and tricyclohcxyl phosphate. The results indicate that

I,ranching c:~uscs a definite inctxasc: in the distribution coefficient compared to that of normal alkyl pliosphutc~s. ivlorcovur, the esistcncc: of branching near the xlkosyl ox-

ygen cnhancc:s tlic* estraction ability to ;i rcmark:il~lc* cstent. ‘I’ri-.s,+c-hutyl pliospliate

c:lcxirly shows ;L tlifferc~nt c:stractiOn bdixviour from that Of tri-n-butyl pliosphiite,

;~ltli~u~li tri-iso-butyl pllospllatc: givc!s ;L curve somcwli;it similar to tlic: latter.

‘I’l10 Iiighly I~r;u~cllccl tricyclolicsyl pliosphatc :ilsr) 11;~s a liigli cstrriction ability wllicll is similar to that of plioslAliiiatc or phospliinc ositlc.

‘1’1~ rcinuxd of tlic! alkosyl osygcn dCfinitdy results in xii incrc;isc in tile cs- traction ilbility. Rut tllc! cllilllgC! in the cstraction ;tbilit>* clots not follow a regular

pilttc~rn, and tllc f<\‘a ~~~~1~s for the phosphorus compounds tcstccl clecrcasc in the

following order: tri-fl-butyl p1lOS~~llilliltC > tri-,dxit_yl phospl~iiic ositlc > tricyclo-

l1csyl pllosplldx~ ZUlCl tri-ax-butyl ~~IlOSl~lli~tC! > tlic:thyl butyl piiosplionate >

plioSpliatcs with normal dkyl groups.

‘I’llc cstraction lllC!C~lli~lliSl~~ w;lS csaniinecl On tllc l~Ornlil1 ;llkyl }~llOSpllilteS. ‘TO

tl(:tcrmiiio tllcl UlIliltiOn Of c~StlXctiOl~, bOtl1 till: SOIVl~llt ilntl ilcitl tlC!p~lldl!l~CX:S were

stutlicxl. ‘I’llc \*ari;ltion of I<,, v:iIuc’s with ‘1’1~1’ cOncc~r1tratioiis, tllc solvent clclx:iitlcnce,

WilS cIctcrniinc:cl o\‘ci’ tlic! ‘1’131’ conccntt’iltioll rilllgC: of 0-_00’%, ancl nitric acid range

0T 2-10 ICI, a.ntl iii aI1 cusc’s ;L plOt of I<d vducs 71s. IX1 concentrations GilVC il scconcl

power clcl~~~i~cli~i~cc. ‘I’hc! acid clcpcncl~.~ncC~ Of the cstraction is Of the fourth power,

:incl is clctc~rmind by plotting tlic Vducs of K,J[_‘f131’]” against the activities of nitric

:tcitl. Wit11 Otlier normid alkyl pliospliatc!s tlic same results wc’rc Ol>ti~illd.

TO test tlic cffcct of Iiytlrog:cn ion conct:iitr~ition, the nitric acid cOllcelltriltiOll

\ViLS Vi~ricCl to I, 3 illlC1 5 M, wllilc tllc total nitrate ion concciltriitiOi1 was ninintainccl

at 5 M l)y i~tltlitioll of scxliiini llitri\tc. Zirconium was then cstractccl with tri-abutyl

~~llOS~~llilt~!. ‘I’llc: rchsults till)\lliLtc!tl in ‘I’ablc 1 Sh0W 1lO proton clcpelldcllCX in the cStlXc-

tion, I~uncc! it may lx concluclctl Clmt tllc 11yclroge1~ ion clots not take part in the c:str:b,ion rcilCZtiOl1.

‘I’otal NU3- conccntrid.ion: 5 &I, ‘L’UL’ conccntmtion: 0.732 Af ---- ^--_-I____- ..__. -_- --- -... . . . . --.-____-_-_

I1 WlC.(l~~I) I.Iz. I.12 3.13 3.15 5.19 5.19 Iid 0435 0*34 0.37 0.38 0449 0.17 1--.-----1-.-._- _._-- I--- 1-.--_-_._-___

‘l’hc Kd vulucs for x0-5 M zirconium solution nncl tracer zirconium solution were fount1 to lx the snmc, thus there WiLS no clcpcntlcnce on the zirconium concentration.

ESTRACTIOS OF Zr WITH ORGANO-p COMPOUNI~S 363

These results indicnte that the reaction mechanism may be written as follows:

Zri4 + 4 (NO:I-).~ t- 2 Wrg)Or, -. [%r(NO:l).r(Org)zloro

‘i’hc evidence that two molecules of organic sol\*ent and four molecules of nitrate

ions combine with one zirconium atom suggests the charge of zirconium to be +q

over the range of z-10 M nitric acid media. For the cstraction of zirconium with tri+t-butyl phosphate. Al_cocK c*t ciL. 5 rcportecl ;I second power solvent clepenclence, and MURUACH ANI) MCVEY~ clen~onstrated that threw molecules of tri-wbutyl

pllospliatc combine \vitli one atom of zirconium.

‘I’lw equilibrium constant for the above estraction reaction was clctcrmincd

only in one case, id!. with tri-a-butyl phosplinto. This constant was calculr~tcd at

various nitric acid concentrations according to the above cstrnction reaction, thr

acid concentrations being corrected by using the i~ppropriate activity cocfficicnts. ‘I’nblc II shows tlw \~llucs obtainccl, the iivcragc of which is taken as the equilibrium constant. This was cletcrminctl to be 1.6. I0 -:! at 23O. bIUIcl3ACH ASI) &‘ICVEY” cl’~l\‘C n value of 5 * x0-3 at 25” for the estrnction of zirconium with tri-wbutyl phosphntc. but tlw wltw was dctermincd on tllcm basis that three solvent molecules combined wit11

‘I’llc cbffcct of tclnl)crilt~lr~ \\‘;I$ ~Sillllill~tl for tllc extraction \vitll tri-lb-butyl pliosplintc!. ‘I’lic results indicxtc tliat tlic tcmlwraturc dq~enclct~ce is ilffCXteC1 1,. tllc nitric acid cOllcelltlXti0ll in tlic nquc~ons ph;~sc ilS ill~lStKltd in Fig. 2. At 1oW acicl concentration. tllc fl’d VillUCS incrcxwc ilS the tc~TnI~crilt~lrc rises. whereas an cntirel> opposite relationship is obscrvetl iit liiglr ncitl C0llcclltKlti0llS. In tlic intcrnicdintc txngc of nitric iLCiCl conccntrution, no ill>l)rC!Ciill)lC tcnipcraturc tlcl~c1lrlcnco is olxcwecl.

‘I’lic infrared spcctr;L of zirconium estrncted from IO M nitric acid solution with tri-ewbutyl phosphatcz, dicthyl butyl pllosphonatc, tri-a-butyl pliospliinate and tri-wbutyl pliospliinc osidc were! mcasurctl. ‘I’hc infrilrCC1 spectrum of the cstracted comples w~ls compared to that of corresponding solvent, and chxngcs between these two spectra were rtnalysed.

364 H. UMEZAWA, R. HARA

The changes observed are not characteristic only for the zirconium complexes: the same changes are commonly observed in infrared spectra of other metal organo- phosphorus complexes. Although the analysis and the interpretation of the changes observed in the infrared spectra of metal organophosphorus complexes will be publish- ed as a separate paper, the following major changes are referred to here: (I) the shift in the P=O stretching ifrequency by complcxing with zirconium, (2) the split of the ionic nitrate degenerate stretching vibration, which is attributed to the covalent

Fig. 3. Infrarctl spectra trf the CXtlYlCtCd cotnplcxcs. il, --- %r -j- tri-JJ-lmtyl phosphinc oxide, - - - - tri-Jr- Imtyl plmsphine oxiclc; I>, - Zt -1_ tri-Jr-butyl phos- pllinate, - - - - tri-Jt-butyl phosphinatc ; c, - %r _t

cliethyl lmtyl phospllonatc, - - -- dicthyl butyl pliosphonntc ; cl, -- %r + tri-JJ-butyl phospkltc,

- - - - tri-Jr-butyl phosphntc.

nature of the complexes, and (3) the change in 1’ -0-C stretching bond, the nature of which is not: clearly understood as yet. Some of the typical spectra are shown in Fig. 3.

The observation of the infrared spectra supports the evidence of covalent complex formation between zirconium and organophosphorus solvents.

ESTRACTION OF zr WITH ORGANO-P COBIPOUNIX~ 365

ACKNOWLEDGEBIENTS

The authors express their appreciation to Drs. KEN JXIXO KISWRA, TAKASHX MUKAIBO, KEICHI OSHISZA AND KEIJI NAITO for their suggestions and encouragement. The

authors are also grateful to Mr. HIDEO KAB~IYA~~A for the interpretation of the

infrared spectra, and to Dr. I~YOICHI UEHARA of Tama Chemical Co. for the synthesis

of the organopl~ospl~orus solvents.

SUBIiLIARY

The extraction of zirconium from nitric acid media with alkyl phosphates, phosphonnte, phos- phinatc and phCJSphinc oxide was studied. The extraction ability is affcctcd by alkyl substituents attached to the phosphoryl group as wcil as by the so~vcnl~ structure, the order of efficiency being: tri-4Jutyl phosphmatc > tri-rz-butyl phosphinc oxide > tricyclohcxyl pltosphstc and tri-set -butyl phosphate > dicthyl butyl phosphate > normal alkyl phosphates. in the cxtrnction With normal nlkyt ~JtwJsI3flatcs, tw\‘o SCJlVCnt m&CUkS Und four llitratc iOilS CctmbinC with CHIC atom of zirconium. ‘I’hc cC~uili~)riu~n constant and thu effect of tcmpcraturc were studied in the cx- traction with tri-wbutyl I3htJS~>hiL$X!. ‘f’hc infrared spectra of zirconium extrnctcd from IO M nitric acid solution with the orgallo~~hosphor~~s stAvcnts were mcrtsurcd ; it was confirm4 that a covak!nt CcJlI-@Cx \VaS fCHWcd.

1~s uutcurs ant cffcctud uric etude sur I’cxtraction du zirwnium, au moycn dc solvants organoplws- phwds, cn milieu nitriquc. Ils ant cxaminc cn particulicr I’cxtraction h I’aidc dc tributylplros~~hatc.

Wschrcibung cincr Llntersuchung iibcr die Izxtraktion vc)n %irkonium mit organischcn Phns- phorvcrbindungcn, h.%Jll&_!rS ‘I’riI~utylphosphat.