reflect the more than tenfold difference in oxygen content of the steels, Figure 7 shows three distributions obtained on samples from experimental Al-killed steels. The shape of the curves for samples A and B as contrasted with that of the curve for sample C reflects the ability of the method to measure the mode of inclusion populations, provided it is assumed that the distribution is unimodal and that at least some of the particles smaller than the unimodal diameter can be measured by the Coulter Counter. Thus, in curves for samples A and B, the modes are 7 and 10 microns, respectively. On the other hand, the modal diameter of sample C could not be determined because the values of the data points on this frequency-distribution curve were still increasing at the smallest particle size measured. However, smaller particles could have been measured if the oxides greater than about 40
microns, which interfere with the counting of small particles, had been “sieved out” of a second as-extracted residue. ACKNOWLEDGMENT
The author thanks a number of colleagues at the Homer Research Laboratories, in particular T. B. Winkler, W. F. Horscroft, and E. H. Kottcamp for helpful discussions, R. D. Thwaite for petrographic examinations of extracted residues, B. S. Mikofsky for assistance in manuscript preparation, and Jane H. and R. W. Goerlich for technical assistance.
RECEIVED for review February 28, 1969. Accepted September 24, 1969. An abbreviated form of this paper was presented at the Pittsburgh conference on Analytical Chemistry and Applied Spectroscopy, Cleveland, Ohio, March 5 , 1969.
Synergic Extraction of Cobalt(I I) with Thenoyltr ifI uoroacetone Tetraphenylarsonium Chloride from Acetate Medium M. S. Rahamanl and H. L. Finston The City University of New York, Brooklyn College, Brooklyn, N . Y. Cobalt has been synergically extracted into benzene with thenoyltrifluoroacetone (TTA) in combination with tetraphenylarsonium chloride [(C6H&AsCI] from acetate medium. The composition of the synergic product at p H 3-8 has been determined. The plot of log D against log hydrogen ion concentration shows an inverse second power dependence on hydrogen ion concentration. The plot of log D vs. log TTA concentration gives a slope of 2. A similar plot of log D vs. log (OAc) gives a slope of 1 and the plot of log D against log [(CsH&AsCI] shows a first power dependence of distribution ratio on [(C6HJ4AsCl]. The synergic complex has been isolated from the organic phase and the absorption spectra of the dark brown compound has been compared with the yellow complex of cobalt formed with TTA only, similarly isolated from organic phase. The synergic complex is not polymeric whereas the complex formed with TTA only is polymeric. The ratio of cobalt, I T A , acetate, and tetraphenylarsonium thus i t is proposed that cobalt chloride is 1:2:1:1; forms a five coordinated anion complex with TTA and acetate. This anion forms an ion association complex with tetraphenylarsonium cation.
PREVIOUS INVESTIGATIONS in this laboratory have shown that thenoyltrifluoroacetone (TT’A) in combination with tetraphenylarsonium cation [(CsH&As+] can produce synergism in the extraction of metal ions from acetate medium. The extent of synergism is almost of the same magnitude as in the systems TTA-organophosphorous esters (1-4) and TTA-tri-n-octyl Present address, Department of Chemistry, University of Michigan, Ann Arbor, Mich. (1) C. A. Blake, C. F. Baes, K. B. Brown, C. F. Coleman, and J. C . White, Proc. 2nd hit. ConJ Peaceful Use A t . Energy, Geneva 1958, p 1550. (2) H. Irving and D. N. Edgington, J. Inorg. Nucl. Chem., 15, 158
(1960). (3) H. Irving and D. N. Edgington, ibid., 20,314, 321 (1961). (4) T. V. Healy, ibid., 19, 314, 328 (1961).
amine (5). The composition of the synergic products in this system, however, are not of the same type. In the extraction of gallium (6) with ITA-tetraphenylarsonium chloride, it had been found that gallium combines with acetate ion in addition to TTA and chloride to form an anionic complex, which forms an ion association complex with tetraphenylarsonium cation which is synergically extracted. This paper describes the application of TTA-tetraphenylarsonium chloride system to the synergic extraction of cobalt from acetate medium. The synergic product is presumably a five coordinated anion which is ion associated with tetraphenylarsonium cation. EXPERIMENTAL
Cobalt-60, 10 mCi in chloride form in 5N hydrochloric acid, was supplied by Oak Ridge National Laboratory. The original solution was diluted to give 80,000 counts per minute per milliliter and was used as stock solution. Thenoyltrifluoroacetone, Fisher Scientific, was used without further purification. Tetraphenylarsonium chloride was supplied by Eastman Chemical Co., New York. All other chemicals were of reagent grade. Benzene was used as solvent. Buffer solutions from pH 1.72 to 6.0 were prepared with monochloroacetic acid and sodium acetate. The effect of pH was determined using buffer solutions of high acetate concentration and cobalt-60 tracer. pH measurements were made with a Leeds and Northrup pH meter Model BC 0407. Radioactivity measurements were made with a RIDL Model 10-8 Well type NaI (Tl) scintillation probe (la/*X 2l/2 inch crystal) coupled with a Model 30-19 amplifier and Model 49-26 Timer Scaler. A Beckman DB Spectrophotometer was used for spectral measurements. ( 5 ) K. Batzar, D. E. Goldberg, and L. Newman, J. Znorg. Nucl. Chem., 29, 1511 (1967). ( 6 ) M. S. Rahaman and H. L. Finston, ANAL.CHEM.,40, 1709
(1968). ANALYTICAL CHEMISTRY, VOL. 41, NO. 14, DECEMBER 1969
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Figure 1. Extraction behavior of cobalt in benzene as a function of pH in acetate media A . 0.05M TTA -0B. 0.05M TTA 5 X IO-* M (csGs)&C
2
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