problem. Our preliminary results indicate the (:-actirk monomers are likely to form the dimer
first and then to polymerize to fibers until a network is formed. Details will be published elseivvhere.
BY G. E. BOYDAND Q. V. LARSOS Contribution from Oak Ridge Xational Laboratory, Oak Ridge, Tenneswe Received October 86,1960
The extraction of heptavalent technetium, initially contained in aqueous acid, neutral salt and in alkaline soliitionp. by a wide varietjr of immiscible organic liquids, including alcohols, ketones, ethers, esters, nitro-compounds, nitriles, amines, hydrocarbons, chloro-hydrocarbons and orgallo-phosphorus and organo-nitrogen compounds dissolved in non-polar liquids was measured. A basic oxygen or nitrogen atom in the organic molecule was necessary to effect, a partition. Quantitative extraction was obtained when the active solvent also possessed an appreciable dielectric const,ant,. Structural effects were evident and with mixtures involving alcohols synergistic actions were observed. The partitioning Tc(T‘I1)species was show1 to be the pertechnetate ion, TcOl-, for which the molar extraction coefficient was concentration inciependent up to 10-3 Ill. Extraction generally was much more efficient from acid than from neutral yalt or alkaline aqueous phases irrtlicsting that the hydronium ion possessed properties especially favoring its ilistribution. The extraction mechanism with amines dissolved in inactive solvents was anion exchange; with the n-alkyl phosphine oxide solutions stoichiomet,ric compic>xeswere formeti in the organic phase; with the alcohols, ketones anti ethers the formation of a cationic comples appeared to be essenti:il.
Reports of observations on the extraction of technetium from aqueous solutions by organic liquids have been few in number and limited in cope.^--^ Accordingly, in developing a rapid Feparation t’echiiique for the isolation of the shortlived fission-product technetium isotopes jt hecame necessary to conduct measurements on the extraction of Tc(T.11) from acid, neutral and alkaline aqueous solutions. Several new correlations of extractabilit’ywith the molecular structure of the organic solvent TTere discovered, and previous observations were greatly extended. These lat’ter may be of interest because pertechnetate ion, TcOe-, is a member of the class of complex ions, hlXe-, which are import’ant in the solution chemistry of a number of t’he transition elements. The magnitiides of the extraction coefficients for many of these elements present in halide ion solutions are determined by the formation constant and by the intrillsic: (Xernst) partition coefficient for the complex ion i n v o l ~ e d . * ~Pertechnet’ate ~ ion is stable in a wide variety of aqueous media so that measurements of its partition should give information on the intrinsic factor in the solvent estraction of 3tructurally analogous 34x4- ions. (1) Presentcd before the Division of Physical Chemistry, 133rd National Meeting, American Chemical Society, Snn Francisco, California, April 13-18 1958. ( 2 ) C . Ferrier and E. SeprC. J . Chem. Phys., 7 , 155 (1939). (J) G , E Boyd, Q. 1’. 1.ilrson a n d E. E. Motta, “Obntrsations on the Clirnrintry of Element 25,” (Abstract ?io. 48), Symposium on the New Elements. Division of P l i y s i c ~ land Inorganic Chernktry, American Chemical Society. Ryraciise, S . Y . , J u n e 28-30, 1948. ( 4 ) F. Morgan a n d 31. L. Sizeland, A E R E C/SI-96, IIarwell, Rngland, December (1950). (.5) W. Goishi arid IT,I?, Libby, J . .47n. Chem. Sue., 74, 6109 (1952). (6) S. Tribalat and J. Beydon. Anal. Chim. Acta, 8. 22 (1953). (ria) E. Alprrositch, “Contribiition t o the Problem of S a t u r a l l y Orcurling Technetium,” Doctoral Dissertation, Columbia University, 1954. (7) J. B. Gerlit. Proceedings of t h e 1st International Conference on the Peaceful Uses of -4tomic Energy, Vol. 7, Section 9B.2, United Xations, 1!)6G, p . 145. ( 8 ) H. Irving, F. J . C. Rossotti a n d R. J. P. Williams, J . Chem. Soc., I906 (19551. (‘3) R. h1. Diamond, THIS JOURNAL, 61, 68 (1957).
Experimental Observations on the solvent estraction behavior of ultramicro amounts of heptavalent technetium were facilitated by using the 60 d Tc951n y-ray emitting isotope as tracer. This activity waB formed by 110 (p.sn) reactions in metallic: molybdenum irradiated with 22 Mev. protons; the amount produced in a typical two .hour bombardment was 6.1 millicuries (yield = 18.2 ppC./pahr.). The procedure for separating “carrier-free” TcYjr* from ryrlotron targets has been desc.ribed.10 The final step in the isolation conjisted in the dissolution of a technetium dioxide elertrodepoait on platinum in ammoniac:tl perosidt. This solution was 2vaporated to drvncss to ensure the formation of Tc(VI1) anrl the residue (NK4TrOl)mas h k e n up with distilled water anll diluted to give 25.00 ml. of solution. Aliquots (usually 100 A ) were taken from this solution for the Pstmction measurements. In several experiments extractions were performed with initial aqueous concentrations of Tc(VI1) between 10-4 and M. These soliit,ions were prepared by dissolving a weighrd amount of pure KTc04 (containing 2.2 X 105 y TcgYp)in distilled water. Sisty-day Tc9jm tracer T ~ added S if a rltdiometric analysis of the equilibrium phastls was to he condurted. Alt,ernatively, concentration rat,ios w r v determined spectr0photometrir:tlly with a C:try IZodel-14 photoclectric recording sprrtrophot.ometer tising the ult,r:r violet absorpotion band of pertechnetate ion in aqueous soliition at 2875 A. Organic solvents of the highest purity were obtained from the Eastman Kodak Company or from the Matheson, Coleman and Bell Company ( L e . , White Label or Rwrlent grade); usually they were not purified adtiitionally. Technical grade tri-n-butyl phosphate (TBP), howevilr, WIS purified by steam distillations.’I Interferenccs by impiirit,ies in the organic liquids were brlieveci to h:ive t)wn ahsmt. However, reagent grade cyr1ohes;inrrl p r q x m ~ion? t from different soiirres gave differcnt t(v1incJtiuni estrwtioris cw’n though g:~s chronintogr:iphic a n d .. . , t)y iiltravinlet, absorpt.ion spectriim mr:tsrirc~ments on its solutions in “Spect,ro-grade” cyc.loliexant~.12Tri-n-o:nt!.lamine (TOA) c%mploved w:is siipplietf 1)y Cnrhon and
Carbide Chemicals Comp:my.
.I t1ifferenti:il titration
(10) 0. E. Boyd. Q. V. I . a w m and E. E.1 I o t t n . J . .Im. C h m . l F c x , 82. 809 (1960). (11) K. Aloock. S. S. Grimlry. T. V. HeaIy, J. Kcnnrdy and H. .4. C. S l r K a y , Trans. Faraday S o c . , 52, 39 (195fi). (12) T h e authors are indeht,ed to J . C. White for tlic piire prepar:itioris-of T O P 0 used in the initial stages of this \\-ark.
August, 1960
980
SOLVEXT EXPItACTIOK O F HEI'TAVALEST TECHSETIUAI
revealed its tertiary amine content to be greater than 97%.la Dimethyldidodecenylammonium chloride (DDA) was obtained from the Rohm and Haas Chemical Company and was greater than 98.5% pure. Extrac,tione were performed in the survey measurements (Table 11) hy equilibrating initially equal volumes of aqueous and organic phase a t room t,emperature. Ten ml. of each phase (with the technetium in the aqueous layer) was added to a 30-ml. glass-stoppered separatory funnel equipped with a Teflon stopcock, and was shaken togdher on a mechanical shaker for 15-30 minutes. Phase separation was effected by a brief centrifugation using a Size 1, Type SD International Centrifuge wherein the temperature remained close t o 25' .I4 Equilibrium phase volumes were estimated t,o f0.1 ml. by draining each from the separatory funnel into 15-ml. graduated centrifuge tubes. The ratio of aqueous to organic volume, VJV,, was reproducible to better than 5%, and in no case did the sum differ from that for t,he initial phases by more than 5%. I n the extraction mechanism studies the aqueous and organic phases were pre-equilibrated with one another before the addition of Ti:(VII) tracer to the aqueous phase so that here V J V , always was close t o unity. The entire volume of each phase was assayed for its yradioactivity with a 4n geometry ionization chamber filled with 40 atm. of arg;on gas.*6 This instrument was exceptionally stabit,, and its response was linear over a wide range of intensities. Gsiing the ion chamber efficiency-yray energy ca1ibr:ition and the decay scherneI6 for 60 d Tc95m it was possible to convert the radioactivity assay readings into absolute disintegration rates and thence into conrentrations of perte,~hnetateion. Thus, in the technetium tracer esperiments the initial concentration in the aqueous phase was between IO-" arid lO-"J mole l i t e r 1 . Radioactivity balances whiish differed by no more than 3Yc from the activity added to the aqueous phase before extraction were obtained in :~11 (he measurements reported. This result siiggested thot errors siich as those caused by the adsorption of pertec.hni.tate ion onto the mdls of the separatory funnel, etc., \twe ahscnt.. 32olar distribution ratios, or estraction coefficients. B,o \wre computed. from the radioactivity (or sprctrophotometric) ,md volume measurements using the definition = Aclivity in total organic phase Activity-in total aqueous phase ~~~
(13) Private rommunicntirin. Ii. B. Brown, 1957. (14) I n a n i n t i v - t i n g recent study C. E. Hiegins and K. II. Baldain of t h i s Laboratory hnv,. shown t h a t t e m p e r a t i m riws [LS large ns 120 ?an he obtninivl i n I.xngrlig ceutrifiisations, cf., A n a l . C h e m . , 33, 238 :I.5) C. J . F301kow~ki,? b i d . , 21, ,348 (1949). (16) H. lIedi(ri6, I r e l i . f " / , g s . $cia. 23, 299 (1950).
>
0
z 4
m
n 0 Lc
m
a
(k)
G(~ncrally,C2L'J wxs detcrmin-d with a precision of =k 5% or better. Eomevcr, when Eao was quite small (i.e., < 0.01) or quite large (ix.,> 100) the precision was no better than because of difficrilties in the phase separations (i.e., occlusion of phasrs), because of statistical errors in the eetimation of the minute quantities of radiowtivity in , sometimes because a few tenths of a one of the p h m ~ s and per cent. of t,he twhnetinm tracer apparently was nonr,xtrtict:tble. The epwtrophotometric estimations of E,o werc less prer'se :mil w ~ r orestricted to a more narrow r:tngo ( i , e . , 0.1 < E>"< 10) t h m wrrc the values obt,ained using the iomctric method. 1-ntler favorable rircumstances, hower. the former procedure may be more reliable in thitt, changrs in the intensity of the unique ultraviolet absorption spectrum of pertechnetate ion are assayed, rather thsrl 2 gross radioa1:tivity assumed to reside entirely in the Tc04ion. Stiidies of t:ir revereibility of the extraction shon-rd, when the phaaes w r e in complete equilibrium, that the value of F k , o T V : ~ indtpendent of whether pertrrhnrta t,r ion was present initially in the aqueous or in t h e organic phase. The ex1 rnctio'i roefficient was also independent of the relative volumos c;f the two rqnilibrium phases. The teniperxturr variation of Ea0 was mmsiirrtl to determine the :ired for maintaining constant temperatiire. In thwe esperimmt:; the immiscible phases were stirred in a tube immcrsetl in a water-bath controlled t,o within k0.1" of tht: dcsircd t,emperature. Samples from each
(1sJ)tiO).
I
--L22 3
2500 3000 WAVELENGTH ( A n g s t r o m s ) .
3500
Fig. 1.-Ultraviolet absorption spectra of prrtechnetat,e ion i n ( A ) water and in various organic phases: (B) cgclohexnnol, (C) 0. I &Iftri-n-octyl phosphine oxidn, TOPO, i i i cyclohexane, (I)) 0.1 .If tri-n-octylamine, TO.1, in cvrlohesarie, and (E) dimethjddidodecen ylammonium chloridr, 1)I)A, in cyclohexane. Molar ahsojbancy indices for aqiivous solutions a t 2-140 and 2880 A . and 605.5 and '22!1O, respectively. phase were taken after a sufficient time t.0 allow for complete phase separation by gravity on cessation of stirring. At 25" the variation of ESo was 35Yc per degree for 1-hexanol and 5.2% per degree for a 10% w./v. solution of tri-noctyl phosphine oxide in a hydrocarbon diluent, corresponding t,o apparent partial molar heats of extraction a t 28" of -5.8 and -9.2 kcal. mole-l, respectively. Because of this relatively small temperature dependence, all extractions mere performed a t room temperature ( i . e . . 25 f 1'). Spectrophotometric examinations of the organic phasrs from several extraction experiments showed that pertechnetate ion, TcO,-, was the partitioning Tc(VI1) species. The characteristic (Fig. 1) ultraviolet absorption spectrum exhibited in aqueous solutions was found with all the organic solutions. A comparison of the spectra for the aqueous and cyclohexanol solutions wit>hthose for the cyclohexane solutions of TOPO, TOA ant1 DDA revealed a 15 f 5 A. shift to the red in the absorption maximum with the latter; the vibrational "fine struct,ure" of the electronic bands also \\-as enhanced. The blurring of the structure in the water and cyclohexanol solutions may be explained i n terms of
G. E. BOYDAND Q. V. LARSOE
990
Vol. 64
tions based on Table I1 may be of interest. (1) The extraction of pert'echnetate ion by aliphatic and aromatic hydrocarbons and chlorohydrocarbons was negligible even when the latter possessed relatively large dielectric constants (vix., 1,2-dichloroethane). A necessary condition for efficient extraction by a pure liquid appeared to be the presence of an electron donor atom in its molecules (e.g., a basic oxygen or nitrogen at'om). (2) The presence of donor atoms in the molecules of the organic liquid was not a suficient condition for extraction. Such measures of solvent basicit'y as are given by infrared frequency shiftsig or by heat of mixing determinationsz0 have indicated ethers and esters to be more strongly basic than ketones or nitro-compounds; yet, pert'echnetat'e ion mas poorly extracted by the former and efficient'ly by the lat'ter classes of solvents. The possession of an appreciable dielectric constant favored extraction by a liquid even when only weak donor atoms mere present in it (21iz., the organonitro compounds). Increasing the dielectric con--L-L_L 1 2 stant of diethyl ether by substituting strongly 0 io 0 15 0 20 OXYGEN TO C A R B O N RATIO electronegative atonis (see P,P'-dichlorodiethyl Fig. 2.--Extraction of Tc(VI1) from normal acid, neutral ether) markedly enhanced extraction despite Ealt and alkaline solutions by straight chain alcohols. indication^'^ of a significant decrease in basicity thereform. Franck-Condon strain and the relaxation time of the sol(3) The extract'ion of Tc(YI1) decreased within vent cage." I n non-polar solvents such as cyclohexane where strain is absent, vibrational structure was preserved. an homologous series on increasing the hydrocarbon character of the molecules. This deExperiments also vere conducted to determine if E,o were independent of the pertechnetate ion concentration. pendence for alcohols, ketones and ethers could be The radiometric method was employed using Tcgj" tracer correlated with t'he 0 : C atom ratio for the molecule in solutions of KTc04 made up t o the desired concentration (1;ig. '2) . 2 1 Increasing the hydrocarbon portion of with fission-product Tcggg. For extraction from 2 S nitric acid solution with cyclohexanol, cyclohexanone and with a an n-alkyl alcohol lowers the number of donor oxydilute solution of methyldioctylamine (MDOA) in ben- gen at'oms per unit volume of organic phase because zene the data (Table I) show that Eaowas concentration in- of the increased molecular weight and because of dependent from lO-IO to M . This result is consistent with thv hypothesis that Tc(VI1) did not occur in a polg- change in density. If the basicity of t#hecarbinol groups is not changed by increasing chain length meric species in the organic phases. it' should be possible to vary the 0 :C ratio, and TABLE I hence Eao,by adding a pure hydrocarbon liquid to CONCENTRATION DEPESDEXCE OF EXTRACTION COCFFICIEATSan alcohol. The results presented in Fig. 3 appeared to confirm this expectation and to suggest FOR Tc(T'I1) IN AQUEOUS 2 N H S 0 3 SOLUTIOVS 5% I V . / V . t'hat it was t'he polar group concentration which Initial TcOdCycloCycloLIDOA in governed the extraction. The data given in Fig. 3 ion corcn., .lf hesanol hexanonc CsHs also yielded a linear relationship when log i?,o 0.31 8.16 8.74 ca. 1 . 5 X was plotted against the mole fraction of hexane, 2 x 10-8 7.98 7.05 8.99 as did extraction dat'a (not shown) taken with 29.22 2 x 10-7 8 . 0 7 8.56 hexanoiie in the same inactive solvent. B thermo2 x 10-6 8 . 5 2 8.55 9.03 dynamic justification for this latter behavior, 2 x 10-5 7.88 8.12 (7.37) first observed in the extraction of indium tracer x 10-4 8.16 8.61 8.78 2 from 0.2-0.5 N HRr by solutions of methyl iso2 x 108.28 9.09 9.41 propyl ketone in cyclohexane and benzene, has A V . 8 . 1 5 f O . 1 5 8.52 5 0 . 2 7 9.12 5 0 19 been given.'% (1)Significant differences in the basicity of cycloExperimental Results and Discussion (18) .\. A . Jfaryott and E. R. Smith, "Tablcx of l>irle(,tric Conbtants Survey Measurements.-The extraction of tracer Piirc Liquids," S R S Circular 514, 1951; A . .I. Pctro. "'I'able of quantities of Tc(T'I1) from normal sulfuric acid. ofDielectric Constants and Dipole JIoments," Piihlication 503, National sodium sulfate and sodium hydroxide solutions, Research Council, 1955, p. 29. Dielectric conqtants for which literarespectively, was measured using 75 diff ereiit ture values could not be found v e r e ineasrired in this u-ork using a organic liquids or solutions. The extraction co- simple, tuned-circuit, radio-frequency bridge. (19) V. Gordy and S . C. Stanford, J . Chem. Phys.. 8, 170 (1940). efficients, Eao, derived from these measurements C. S. Marl-el. A f . J. Copley and E. Ginshrrp. J . Am. Chem. Soc., are summarized in Table I1 which also presents 62,(20) 3109 (1940). value for the static dielectric constants for the (21) A similar correlation in theextractionof uranyl nitratr by P t l i c r s moisture-free liquids taken from the literature,I8 has been noted by E. Glueckanf, H. A . C. McI ith aolutioiis of 1hexanol in n-lic~\xie(filled circles).
This finding was not unexpected as molecular structurr controls the density and hence the donor group concentration in an organic liquid, its dielectric constant and influences the basicity of the donor groups i n its molecules. Alcohols.-(a) Tertiary alcohols were lxttcr e\t ractantc. than secondary or primary alcohol< of t lic -ame 0 :CJ atom ratio. l'rewmably, the tertiaiy alcohols are le%ldi-n-octylamine (Table 11) may be considered a consequence of the larger size of the former, if the difference in shape can he neglected. Extraction from Acid Solutions.---Furt her inveqtigntioiiq with acid solution.. w m e d desiro blc one of the intereitiiig facts r?ve:ilrd by Table I was that while the extraction of Tc(Y1I) from I ~ I tral salt and alkaline aqueous solutioiiq TEE quite incomplete with acid solutioiis quantitative exrr:iction was observed. Results from nieasurements with normal solutions of several strong acids shcned (Tnblc 111) that a correlation for a variety of solvents existed betn-een the extraction of pertechnetate ion and the nature of the acid anion. Acid extraction into cyclohexanol was ( 2 1 ) Q r c lor m a m p l - t h e dlvu-ion h v Cr. TI 3Inrn.on a n d I1 Soli ent l'.;tm, t i o n in 4nal)tical Clieiiii-tri John N i l < \ d i i i l rrel-er Son- I n c V P U I o r h . S T I1957, p 70 ( 2 5 ) R. A i Diamond, Tail. JOUR\AI.,63, 659 (lo501 ,I'
ExrR.uxiuN Sol--ent
UF
TABLEI11 Tc( 1-11)F R U M XORMAL SOLUTIONS OF VARIOUS STROSG ACIDS,E,o H,POI
HzSOI
HC1
HXOI
HBr
HI b
HC104
15 12 8.8 5.5 4.3 0 . 05c 0 . 18c 0.29' 0.41' 0 . 5gc 0.48" Cyclohexanone 93 51 25 14 5.1 2.6 0.40 0.12 0.031 0,074 0,001 p,p'-Dichlorodiethyl ethcr ..... 1.5 Tributyl phosphate ..... 44 120 91 29 70 5.6 48 25 65 0.24 Tri-octylphosphine oxide" 130 51 0.46 74 110 580 74 3.6 0.44 26 Tri-oc tylamine" Even at quite small concentrations pertechnetate ion is thermodynamically unstable t'ouard 5 0.1 M in cyclohexane. reduction by N HI. Possibly the valence state extracted from this acid was Tc(V). Extraction coefficient for acid.
Cyclohexanoi
210 o,0277" 130
32
measured also, a,nd the Eaovalues are given in the second row of Table 111. With this solvent a t least, the extraction of pertechnetate ion decreased as that of the acid increased. An anion-exchange mechanism between Tc04- ion and the anion of the acid W:LS involved in the extractions effected by tri-n-octylemine solutions. A similar dependence on the nature of the acid anion was shown by the other exti*actants; possibly they also extract Tc(1'II) bj. an ion-exchange mechanism. The dependence of the extraction of Tc(VI1) on the concentration of acid initially in the a.queous phase was determined. With pure cyclohexanol (Fig. 4) the extraction increased rapidly upon the addition of small amounts of acid, and, after a maximum Eao value was reached at, or below, 1 &IT, an exponential decrease set in.*6 Curves similar to those in Fig. 4 also were observed with cyclohexanone, wit'h pure tri-n-butyl phosphate and with solutio-ns of T B P in a liquid hydrocarbon; maxima in the d u e s of E a o were exhibited at sigiiificantly lower acidities, however. The rate of decrease in the extraction coefficient for cyclohexanone wit,li acid concentmtion past the maximum x i s much greater than for either cyclohexanol or TBP. Presumably, such behavior reflects the increased miscibility of the ketone 1vit.h strongly acid aqueous phases. I n other w ~ r k it~ also ~ , has appeared t'hat decreases in Eaoalways coincide with gross changes in phase volumes on equilibration. Complications because of interphase solubilities may be minimi:eed if dilute solutions of strongly hasic extractants in hydrocarbon or other inactive liquids are employed. Accordingly, measurements of the acid concentration dependence of 'l'c(V11) vere performed with deci-molar solutions of tri-n-octylphosphine oxide, tri-n-octylamine and dimethyldidodecenylammonium nitrate i n cyclohexane. Maxima in the variations of ICa0 wit,h acid molarity were observed with the first two compounds for concentrations of acid a t and helnw 0.1 S (Iigs. 5 and 6). I n the case of the amine the decrease below ca. 0.05 N was probably i~ coilsequence nf the hydrolysis of its (nitrate) salt; the decrcase above this concentration reflcct.ed tht: exchange of Trod- by the competing SO,- ion. S o maximum was found with 0.01 ( 2 0 ) T h p variation of E,O shown for €IC1 solutions a b o v p A .V doc's not represent , h e behavior of 'Tc(V11). At and above this concrntration increasing amoiinte of T c ( V ) werP formed hy t h e reduction of pertechnetate ion h y i~iiloridi~ ion. 127) 11. Irving and F. J . C . R w s o t t i , Annliysl, 7 7 , 801 (1952). ( 2 8 ) D. E. Uetzler and R. .J. Alyers, J . Am. Cham. Soc.. 73, 3770 (1Y50).
17 1
1
I
0
~ ~
2
I
I
1
~
4 6 8 4 0 1 I N I T I A L ACID NORMALITY
Ai 2
1
4
Fig. 4.--hcid concentration dependence of the extraction of Tc(VII) from aqueous acid solutions by cyclohexanol.
JI solutions of the quaternary ammonium salt dissolved in toluene (Fig. 6).29 A qualitative explanation for the linear decrease in log Eao for TcOa- ion concentrations less than 10-5 11 with the log of the acid concentration (Fig. 6), and for the linear increase with the log of the tri-n-octylammonium nitrate (or dimethyldidodecenylammonium nitrate) concentration in the organic phase (Table IV) can be based on the assumption that a mass law governed anion exchange equilibrium occurred _____ R4K+NO7-+ Tc04- I_ R4?jl'Fc(Y4- + 10,-( I j \\-here the bar denotes the organic phasc. 'l'he equilibrium concentration product quotient is then
and, for a constant nitrate ion concentrntion in t'he organic phase, Eaowill decrease inversely as the (20) T h e departnrm from a straight line of nnit negative slop" below 0.05 ,V HNOa in FiE. B are believed t o have hcen caused by rniniite amounts of technetium irreversibly adsorbrd on CiiS and other colloidal impurities in the radio-tracer preparation.
G. E. BOYDS N D Q. V. LARSON
994
T'ol. 64
TABLE IV EXTRACTION OF PERTECHNETATE IONAT TRACER CONCENTRATIOSS IK AQUEOUS NITRICACID SOLUTIOXS B Y PREEQUILIBRATED ORGAMC SOLUTIOSS OF .~MMONIUM SALTS Molarity Ea0 Q A. Dimethyldidodecenylammonium nitrate in toluene: 1N " 0 3
CDDA 0.0005 00075
,001 ,0025 .005 .Ol .05 .10 0.1 M T O P O \ I N CYCLOHEXANE
0.40 .63 .76 2.00 3.59 6.39 26.3 45.3
802 842 756 800 718 639 526 453
B. Tri-n-oetylammonium nitrate in a hydrocarbon solvent: 2 AT HXOZ
\
CToA
NORMALITY OF H N O J 1
Fig. 5.- -Extraction of Tc(VI1) from aqueous nitric acid solutions i)y tri-n-octyl phosphine oxide (TOPO) solutions in hydrocarhn solvcnt.~.
i A
'C 3
Fig. (i.--Estraction of Tc(T'I1) from aqueous nitric acid solutiom 11)- 0.01 J I tri-n-octylamine ( T O h ) in cyclohexane and by (1.01 -1f dimeth~ldidodecenylammonium chloride (1)D.A) in toluene.
first poiver of the nitrate conceiitratioii in the aqueous phase provided thermodyiiamic artivity coeficieiit variations niay be ignored. The failure of this 1:ttter approximation may be the cause for the depwtures of the points a t the highest concent,rations in Fig. 6 from the unit slope straight
0.015 ,0283 ,0283 .06 .14 .25 .43 .65 .85
0.90 2.0s 2.21 3.92 9.60 18.7 39.7 41.7 67.8
120 144 156 131 137 149 185 128 160
lines. In addition, excess nitric acid over that needed t80 form animoiiium salt in the organic phase was found to be extracted: alternatively, t,his may have been the cause of the deviation. I n applying the mass lam- to systems wherein the concentration of ammonium salt in the organic phase was varied, it was assumed that the species R4N+N03- or R&H+XO3- were monomeric. ?\To direct measurements supporting this assuniption have been reported ; however, light scattering and other studies n-it'h solutions of tri-n-octylamrnonium sulfa,t,e in benzene have indicated this salt t,o be molecularly dispersed.3u It seems 1 likely that dimethgldidodecenylaiiinioiiium nitmte would be unassocinted even in organic solutions after considering the extensive researches of Kraus31 on similar compounds. The decrease of Q with increasing DDA coiiceiitrxtlioii shown ill Table I T r may therefore be a result of an increasingly complex organic solution. The dielectric constant of the i1iactiT.e organic solvent for ammonium and ot'her salt-type (>ompounds may influence their efficiency for extraction if electrolytic dissociation c m l ocmr i n the organic phase. The measurements reported in Table T' show that the extraction of pertechnetate ion was the most cwmplete nhcn soli-ent,s of high dielectric coiistaiit w e r e used. X similar dependence was observed wit'h s:olutions of tri-noct,ylphosphine oxide altzhoughwith t,his cwnpcxuid chloroform prohahly is iiot a i l inactsi\.cdilwiit'. Son-ideal behavior by the foregoing org:riiics solutions may sometimes govern their solvent (30) K. h. .illen, T H I S JOURXAI,. 62, 111H (l!)a8). (31) C. A. Kraits, ib7d., 6 0 , 139 (1956).
SOLVENT EXTRACTIOS OF HEPTAVALEST TECHNETIUM
August. 19io TABLE V
H,SO1 BY SOLUTIONS OF EXTRACTTOS O F Tc(T-11) E R O M 1 'O'O TRI-~L-OCTYI, I'HObPI I I N E OXIDE(TOPO), TRI-n-OCTYLAMINE (T0.1) A m D I ~ I I : T I I Y L D I D O D E C E S Y L . ~ ~ I ~ ~ O NSELFATE I~~f (DI)A) I S VARIOUSIXERTSOLVESTS ---Extraction
Diluei: t
TOPOa
1,2-Dichlorocthane Chloroform Benzene Carbon tetrachloride Di-isopropyl ether Cyclohexane Hexane 0.01 solut,ions.
27 0.077 .63 .13
r---
'
'
995
7
'
coefii:ient--DDA b
TOAa
200 120 110 110 . '31 100 .41 81 .57 96 i, 0.001 S solutions.
190 120 40 17 15 8.6 8.2
2
/
-
0
c
2c z
/ 0.4
t
0
est,ractioii efficiency. Thus, association of the solute to gi\*e low molecular weight micelles will I. lower the ljhermodynaniic activity of the salt aiid reduce extraction. The molecular structure of L L L 1 A L L L 0.004 0.ci 3,' '.3 the amine (cf. Table 11) may determine the N I T R I C A C I D NORMALITY. degree of its int'eractioii with t'he solvent as well as I.'ig. T.-Variation of t'he extract'ion of Tc(\'II j int,o cy+its tendelicy to form micelles, and hence the exa i t h acid concentration in HS03 + NaSOa mixtraction efficiency of t h e solutions of its salts.32 hexanol tures at 1.0 Af. Straight line obtained by subtracting limitAssumiiig that t'he extraction of pertechnetate ing value of = 0.32 from observed values. ioii by organic solutions of TOPO (and tributyl phosphate) iiivcllved the formation of complex TABLE VI which reac1,ed according t,o H'
+ TcOl- + 4TOPO I- HTcO4,qTOPO
applica tion of t h e law of mass gives = log K log [H+] q log [TOPO] ( 4 ) log where [TOPO] '1s the t'hermodynamic activity of the uiicomplexecl reagent which may be taken as monomeric.33 Concentrations may be employed instead of acAivities for sufficiently dilute TOPO solutions; when this was done (Table VI), the extraction data were found consistent with y = 2. Xdduct number:, of two have been r e p ~ r t ' e dfor ~~ t'he extraction of dichroniat'e, Zr(IV), Mo(YI), T(VI), Ti(1Y:) a n d Sii(1T') from acid aqueous chloride, sulfa--e mid iiitrate solutions. The extract,ioii of Th(IT-j n-ith TOI'O appears to be except,ioiial; here, q = 3. The iiicirease in extraction of hept'avalent t,echiiet,ium with increasing acidit'y at low coiiceiitrat,ions observed n,ith alcohols (Fig. -1) and ketones may he explaiiird hy 3 ssuming that iiicreasiiig amouiit's of salt (i.e , ion pairs) were formed in the organic phase by rextion of the basic solvent S with acid
+
+
TRACER COXCESAQUEOLSACID SOLVTIOSS B Y PRE-EQUILI-
EXTR.4CTIOS OF PERTECHXETATE I O N AT
(3)
TRATIOSS BRATED
IN
ORGASIC
SOLUTIONS
OF
TRI-n-OCTYLPIIOSPHINE
OXIDE .\lolarity
E?,O
E,~/:Croro%'rr\-o3)
TOPO in hydrocarbon solvelit: 2 S HSOs 0.0215 ,043 ,086 .17 .23 .35
0.0188 ,0307 ,0967 ,569 1.02 3.42
3 . 3 X.30 (i. 5 4 ! I . 84 ! I . 6-4 1:j. 0
TOPO in carbon tetrachloride: 1 -Y IICI" r 0.0041 0,0129 /bl ,0103 0514 485 0207 ,003 21; ,031 ,241 35 I ,0413 ,420 24(i ,1033 2.25 211 .2066 0.37 320 Extraction b y pure CC14gave Eao = 0.00:1. 4-
the aqueous phase. If the aqueous iiitrate ion coiicentratioii is held constant Eao for Tc(T'I1) H,O+~(H,O)nSm.S03- ( 5 ) should increase linearly with the concentration of r , I his salt, n-hich alternatively may be S H f . (H?- H30f.(H?O),SmKO,?-, aiid hence with the aqueous O),S,.SO, -, ma!: then react, n-it'h trace amounts of acid conceiit,ratioii. This expectatioii a,ppeared to pert$echnet:ite ion in aqueous solutio11 by ion ex- he confirmed by nieasuremeiits of the extraction chaiige to give H,O+. (H,Oj,,S,.TcO,-. When only of t'echiietiuin froin constant ionic st'reiigth aqueous small amoiuit's of ITS03 are in the organic phase it solutioiis by pure cyclohexanol (Fig. 7). Extraction from Salt Solutions.--Relative to :lcicl is expect,etl that t,he ronceiitrstion of salt. mill be linearly proportioid t'o the nitric acid ncttivity in solutions Tc (T7.I) was poorly extractctl fi~oiiiiiorilia1 neutral salt :uid strong-haw solutioiis (Talile 11). Sonetheless, an exitmiiiation of t,he fartors uhich appeared to govern t'he part'itioii with t,he lat'tcr seemed wort'h while. AIeasureineiits \vit,h strongly basic extract'ants dissolved in iion-polar .iST31 S'rP 2 ' 8 . .1111.Sei( f o r Tc-rin:: 3lsteri;iis, P l ~ i l i i d c l ~ ~ lPa,, ~ i a . organic*liquids were not rarried out lxra1,isc it n - ; ~ c.oiisiderec1 that the est'ractioil inecha iiisni nit11 1!E8. H,07 f
+ ,tH20 + m S
,
~
G. E. BOYDAKD Q. V. LARSON
996
'I
NoNOJ
- 1
_._-_I
---
1
._
-1-
--
I
I- _ 1 - - _ 1
NORMALITY OF AOLEOJS SOLUTION
rig. 8.-Extraction of heptavalent technetium from aqueous salt solutions by cyclohexanol.
0
1
--
t
10
PO
30
NORMALITY
OF ACb,OU5
40
5 3
6 0
SOLUTION
Fig. 9.--Extraction of heptavalent technetium from aqueous salt solutions by tri-n-butyl phosphate (TBP).
Vol. 64
information on the solubilities of the various sodium salts in pure TBP.*s For example, the solubility of NazSOain the TBP is extremely small (0.00022 molal) compared with NaC104 (1.11 molal). Further the sequence of extractability of the sodium salts from their aqueous solutions into T B P a t 25" is: NaC104 > NaNOs > NaC1. Sodium pertechnetate, by analogy with NaC104, should be appreciably soluble in T B P and should be extracted efficiently by this solvent from its own pure aqueous solutions. I n the extraction of microamounts of pertechnetate ion from concentrated salt solutions "salting-out'' effects in the aqueous phase and competition in the formation of TBPsalt, complexes in the organic phase must occur. The initial rapid increase of Eaowith increasing salt concentration shown in Figs. 8 and 9 was probably the consequence, however, of the increasing sodium ion concentration. If the salt in the aqueous solution in which pertechnetate ion is contained possesses a high thermodynamic activity Eao should be increased. Thus, for example, if LiN03 were the salt a higher pertechnetate ion extraction would be expected than if KNO, were used. Distribution measurements showed that such differences did occur between electrolytes in the anticipated order but that these were significantly larger than was expected (Table VII). This outcome suggested that the extent of cation solvation and ion-pair dissociation in the organic phase was likely t o be important. Tke data presented in Table VIII, in contrast t o those in Table YII, may be taken t o indicate that the relative contributions from these two factors may be different: With T B P strong solvation forces favoring the small cations may be involved, whereas because of the high dielectric constant of nitromethaneaR all the alkali pertechnetates must be ionized extensively in the organic phase. I n the latter case salts with large cations should extract better than those with small cations of a similar structure.
them was simple ion exchange. It did not seem probable, however, that the extraction of Tc(VI1) hy pure alcohols, ketones, nitro-compounds and by TABLE VI1 tributyl phosphate from neutral and alkaline soluEXTRACTION OF Tc(VI1) FROM 1 M NITRATESOLUTIONS BY tions occurred by such a process. Data presented TBI-n-BUTYL PHOSPHATE in Figs. 8 and 9 for cyclohexanol and tri-n-butyl E . Aqueous soln. Aqueous s o h . E.. phosphate, respectively, show the dependence of "03 28.3 KN03 1.1 pertechnetate ion extraction on the anion of the LiNOa Ca(N03)~ 15 6 14.7 salt and on the concentration. Heptavalent tech",NO, C~(N03)2 5.4 4.6 netium, with all solvents, including methyl ethyl NaNOa Al(N0a)a 4.4 2.2 ketone and cyclohexanone for which data are not shown, was extracted t o the greatest, extent from TABLE VI11 sodium sulfate and least from sodium nitrate or EXTRACTION O F Tc(VI1) INTO NITROMETHANE FROM NEUsodium perchlorate solutions. Maxima in the TRAL, MOLARAQUEOUSSOLUTIONS OF THE ALKALICHLO variations of Eaowith salt concentration were absent RIDES except possibly in the extractions from sodium Ea0 Salt 88 Salt perchlorate solutions by tri-n-butyl phosphate and LiCl 0.55 KC1 2.1 from sodium hydroxide solutions by cyclohexanol. NaCl 1.2 RbCl 2.5 The relatively efficient extractions from Na2S04 HC1 1.6 CSCl 3.7 solutions could have resulted if small amounts of (35) T. V. Healy and P. E. Brown, "Extraction of Alkali Salts into free acid had been present; pH measurements Solvents," AERE-E/R-1970, Harwell, Berks., England, J u n e always showed these solutions to be close t o neutral, Organic 6, 1956. however. (36) H. L. Friedman a n d G. R. Haugen. J . Am. Chem. SOC.,76,2060 The data in Fig. 9 appear to he consistent with (1954).
