4289
NOTES
The Extraction of Thallium(II1) from Aqueous Chloride Solutions by Tributyl Phosphate in Octanela
by H. Michael Widmerlb and R . W. Dodson Chemistry Department, Brookhaten National Laboratory, Upton, A'ew Yorlc 1197.3 (Receiaed M a y 22, 1970)
In measurements of the stability constants of chloride complexes of thallium(III), Walters and Dodson2 used tributyl phosphate diluted with hexane to extract the species T1C13 from aqueous solutions. The present investigation with n-octane as diluent extends their work and includes quantitative characterization of the distribution equilibria of HTlCl4 and TlC13. As in the earlier work2 all organic solvents were carefully purified. 204Tlwas used as tracer. It was proved that distribution equilibrium was attained. The temperature was 25.0". Equal phase volumes were used. The ionic strength of the aqueous phase was 0.50 M , maintained with suitable mixtures of stock solutions of HCl, HC104, NaC1, and NaC104. The observed distribution ratio D is the ratio of the concentration of thallium(II1) in the organic phase to that in the aqueous phase. The expected dependence of D on the concentration variables is obtained by considering the reactions
+ mTBP,,, = T1Cla~mTBPorg + TlC14-aq + nTBPorg = HTlC14.nTBPorg T1C13.,
H+aq
(1) (2)
and their equilibrium constants KD3 =
[T1C& mTBP]org/ [TIC13Iaq [TBP]"org
and
K D =~ [HTlCh. nTBP]org/ [H+]aq[TlC14-]aq [TBP]"org The omission of activity coefficients of species in the aqueous phase implies the assumption of constant medium, which is a fair approximation at the ionic strength used. The corresponding omission for species in the organic phase limits the constancy of the mass action expressions to a range of T B P concentrations in which the appropriate activity coefficient ratios remain constant. With this limitation the distribution ratio is given by
D
= a3K~3 [TBPI"org
where
a3
and
a 4
4- ~ l & ~ d [ H + ] a q [TBPI'org
(3)
are the fractions of the thallium(II1)
in the aqueous phase present as T1C13 and T1C14-, respectively. Dissociation or polymerization reactions in the organic phase were shown to be unimportant by the finding that D is independent of the concentration of thallium(II1) in the organic phase under all conditions studied in the present work. The ranges were 4 X M when to 2 X and 5 X lo-' to 2 X the principal extracted species were TICla and HTlCL, respectively. With 0.0365 M T B P no appreciable change (less than 6%) occurred in D as [H+]&,was varied from 0.002 to 0.50 M. These measurements were made a t [Cl-I,, = 0.006, 0.10, and 0.50 M . However, a marked effect of acid was found with 0.730 M T B P a t [Cl-],, = 0.50 M . The values of D were 119, 204, 285, 413, and 475 at [H+Iaq= 0.10, 0.20, 0.30, 0.40, and 0.50 M, respectively. These results exhibit the linear acid dependence required by (3). They also show that the T B P solvation number of the extracted HTlC14 is greater than that of the extracted T1C13. Estimates of the solvation numbers m and n were obtained from the variation of D with [TBPIorg. Values of log D are plotted vs. log [TBP],,, in Figure 1. The curve on the left is for the extraction of TlCla. A straight line of slope 2.0 is a good fit to the data3 throughout the 100-fold range in concentration. The slope is well established for solutions which are sufficiently dilute that activity coefficient variations can reasonably be neglected. The lack of significant deviations above 0.0365 M (1 vol %) T B P suggests that the activity coefficient of T1C13 2TBP decreases with T B P concentration in a way which largely cancels the effect of the considerable decrease of the activity coefficient of T B P i t ~ e l f . ~The , ~ curve on the right represents the extraction of HTlCl, from 0.50 M hydrochloric acid. The experimental distribution ratios were corrected for the extraction of T1Cb by subtracting calculated values of the first term on the RHS of (3). The corrections (1) (a) Research performed under the auspices of the U. S. Atomic Energy Commission. (b) T o whom correspondence should be addressed a t Department of Chemistry, University of MassachusettsBoston, Boston, Mass. 02116. (2) R. M. Walters and R. TV. Dodson, "Solvent Extraction Chemistry," D. Dyrssen, J. 0. Liljenzin, and J. Rydberg, Ed., NorthHolland Publishing Co., Amsterdam, 1967, p 71. (3) These results agree with observations made earlier by R . W. Dodson and R. M. Walters, which are unpublished except for an allusion in ref 2. (4) K . Alcock, S.8.Grimley, T. V. Healy, J. Kennedy, and H. A. C. McKay, Trans. Faraday Soc., 52, 39 (1956). (5) D . Dyrssen and Dj. Petkovic, J . Inorg. Nucl. Chem., 27, 1381 (1965). T h e Journal of Physical C h e m k t r y , Vol. 74, No. 84, 1970
NOTES
4290
earlier estimates.2) T h e results were K D = ~ 9.7 X IO2 M - 2 and K D =~ 3.4 X l o 3 The value 2 found for the T B P solvation number of T1C13 agrees with the result of Chuchalin, et al.,’ which was obtained by quite different methods. We consider it well established for straight-chain hydrocarbon solutions. Earlier estimates of the T B P solvation number of HTlC1, differ among themselves and from our provisional value 4. A value 2 was reported8 for isooctane diluent. Studies with benzeneg~l0 gave 3, a value expected on the basis of the model proposed by Tuck and Diamond” for the extraction of strong acids. A solvation number 4 was reported by Rleyers and for HFeC14 in diethyl ether-benzene mixtures. They suggest that in dddition to solvation of the hydrated proton there may be a sufficiently strong interaction of extractant molecules with the anions or with the ion pairs that this additional “electrostatic solvation” plays a significant role in the extraction process. We think this is a reasonable point of view and that the HTlC14TBP-octane system may also be an example. lo-’
10-2
IO0
M [TBP]
Figure 1 . Variation of dislribution ratios with concentration of TBP. Left-hand curve, slope 2.0: extraction of TlC13; [Cl-] 0.0060 MI [H+] 0.04 and 0.05 M . Right-hand curve, slope 4.0: extraction of HTlCla from 0.50 M HCl. Values corrected for extraction of TlC13from this medium.
were calculated from results of Walters and Dodson2 and the present work. An alternative calculation of the corrections was made using the stability constants of T1C13 and TlC14- reported by Woods, et aL6 The difference in the corrected values of D obtained by the two methods is taken as a reasonable estimate of the uncertainty in the corrected value and is indicated by the plus and minus error bars. It is remarkable that within these uncertainties the data for the extraction of HTlC14 are all satisfactorily fit by a straight line of slope 4.0, over a range of lo4 in the corrected distribution ratio. We provisionally adopt the simplest interpretation of this result, which is that the extracted HTlC14 is solvated by four molecules of T B P and that the activity YT is the activity coefficient coefficient ratio y ~ ~ / y(where 4 of T B P and y4 is that of the solvated HTlC14) remains constant up to the highest T B P concentration, 0.73 M . For an ion pair, which the HT1C14.nTBP may be supposed to be, it is not surprising that y4 should vary strongly with increasing polarity of the medium. However, we have no basis for predicting so exact a compensation of effects as appears to prevail. The distribution equilibrium constants were evaluated with the aid of (3), on the basis that m = 2 and n = 4. (The stepwise stability constants of T1Cl3 and TlC14- involved in the calculations were independently determined in the present work and agreed closely with The Journal of Physical Chemistry, Vol. 74, XO.24, 1970
Acknowledgments. We are grateful to F. Silkworth for solvent purification, to James R. White for preliminary measurements on this extraction system, and to Karin Karlstrom and Kathleen JIcLinskey for skillful technical assistance. (6) M. J. M . Woods, P.K . Gallagher, 2 2. Hugus, and E. L. King, Inorg. Chem., 3, 1313 (1964). (7) L. K . Chuchalin, I. A. Kuzin, K . F. Obzherina, T . T . Omarov, and L. S. Chuchalina, Russ. J . I n o ~ g Chem., . 12, 622 (1967). (8) K . Henning and H. Speclter, Z. Anal. Chem., 241, 81 (1968). (9) K. S. Venkateswarlu and P.Chanan Das, J . Inorg. Nucl. Chem., 25, 730 (1963). (10) H. Specker and W. Pappert, 2. Ano~g.Allg. Chem., 341, 287 (1965). (11) D. G. Tuck and R. M. Diamond, J . Phys. Chem., 6 5 , 193 (1961). (12) D . A. Meyers and R. L. McDonald, J . Amer. Chem. Soc., 89, 486 (1967).
Ozone Filter for Selecting 185-nm Radiation from Mercury Vapor Lamps’
by L. C. Glasgow and J. E. Willard Department of Chemistry, University of Wisconsin, Madison, Wisconsin 65706 (Receizled June 17, 2970)
Ninety per cent of the radiation from a low-pressure Hg lamp is emitted in resonance lines at 254 nm and 185 nm, the 254-nm line being typically 4 to 10 times2 (1) This work has been supported in part by the U. S. Atomic Energy Commission under Contract AT(l1-1)-1715 and by the W. F. Vilas Trust of the University of Wisconsin. (2) B. T. Barnes, J . App. Phys., 31, 862 (1960).
