Ion Exchange Separation of Fission Product Rare Earths with a-Hydroxyisobutyric Acid MARK M. ZELIGMAN Lawrence Radiation laboratory, University of California, livermore, Calif.
b Separation of the light rare earths from each other has been accomplished using milligram amounts of each available rare earth. The separations were accomplished using the technique of concentration gradient elution with Dowex-50 ion exchange columns and a-hydroxyisobutyrate solution as the eluant. By using fission products as radioactive tracers, good separations were achieved with peak-to-valley ratios of 1 02-104.
S
EVERAL IOX EXCHANGE PROCEDURES
have been developed for separating milligram quantities of the rare earths ( 5 ) ; in general these have entailed the use of heated (-90" C.) columnsandtor long periods of time. Recent investigations (1, 4, 6) have shown that the use of ammonium a-hydroxyisobutyrate solution in conjunction with Dowex-50 ion exchange resin can quickly and effectively separate the individual rare earths a t room temperature. The previous inrestigators (1, 2, 4, 6) used gradient elution techniques to reduce the length of time required and improve separation of rare earths. Their approach has been to vary the p H of the eluate with time while holding the concentration constant. In this study the p H of the eluant is held constant a t 5.2 which is easy to control and reproduce, while the concentration is gradually increased. The experiments described below were undertaken to determine optimum conditions for separation of milligram quantities of rare earths. '-
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OPTIMUM ELUTION IACTIVITY I
EXPERIMENTAL
Apparatus. The gradient elution apparatus is similar to t h a t dep-ibed by Xervik ( 3 ) . (Several columns may be operated from one set of flasks by delivering the eluant to the columns through Y connecting tubes.) The columns were 30 inches long by 7-mm. i.d. with outer spherical ground glass fittings on bottom and top. The columns were loaded to a height of 22 inches with cation resin and were prepared for use by equilibrat'ing the resin with about 100 ml. of the initial eluant a t a rate of 0.5 ml. per minute. Reagents. R A R EEARTH CARRIERS. The oxides of all-rare earths (Y, T b , Gd, E u , Sm, S d , P r , Ce, La) were dissolved individually in 6-11 HC1 and diluted to 1 liter, adjusting the final HC1 concentration to 2-11, These solutions were standardized by gravimetric methods ( 3 ) . The rare earths oxides used were greater than 99.8y0 pure. Promethium-145 was used to determine the position that Pm would occupy in the elution of the rare earths. The a-hydroxyisobutyric acid was procured from Continental Chemical Co. of Sacramento, Calif., under the brand name of Con-0. Solutions of ammonium a-hydroxyisobutyrate were made by adjusting the acid to pH 5.2 with SHIOH. The cation-exchange resin, Dowex-SOW-X 8, dry mesh designation 100-200 mesh, [60-140 wet mesh] was obtained from Bio-Rad Laboratories, Richmond, Calif., and used directly. Procedure. Radioactive tracers were obtained from a n aged fission product mixture. hpproxirnately 8 mg. of each rare earth and Pml45 tracer were added to the mixture, and the rare earths as a group were purified from other fission products by routine radiochemical procedures ( 5 ) . The last step of this procedure was the precipitation of rare earths with XH40H. The precipitate was dissolved with 5-8 drops of concentrated HNOs, diluted to 30 ml. with HzO, and equilibrated a t room temperature with 1 ml. of settled Dowex-50lT-X 8 resin. The mixture was stirred for 5 minutes, the liquid decanted from the srttled renin, and the resin transferred to the top of a previously prepared cation-eschange column. The flasks of the gradient-elution equipment were filled with 0 . l J I am-
350 ml. of the 0.4M solution were needed for each column. Air pressure of about 3/4 p s i . was applied to the system so that the liquid flow rate was about 1 drop17 seconds from each column. The 0.4M solution was not added to the lower reservoir until the yttrium had been eluted (about 5 hours). Aifter the yttrium had been eluted, the eluant in the upper flask (the 0.4M solution) was allowed to drip into the lower flask at a rate equal to the liquid flow rate-Le., 1 drop/7 seconds, column. With these conditions, the molarity of the eluant passing through the column was constant for about 5 hours, and then increased a t a rate of 0.0085 molar unitslhour. The eluate was collected in 10-minute fractions by culture tubes in an automatic fraction collector. The individual rare earths were located by adding a few drops of oxalic acid to each tube. Following elution from the columns, each tube was counted on a well-type gamma-ray counter to determine rare earth separation. The tubes with precipitates were then combined by element, and were washed, dried, ignited, and weighed. After weighing, the samples were mounted on planchets and the decay of the radioactivity was followed on appropriate counters to determine purity. The gamma ray spectrum of each element was measured as a further check on its purity. RESULTS
Separation of the rare earths is still achieved when the drip rate from the 0.4.11 ammonium a-hydrosyisobutyrate into the 0.1X ammonium a-hydroxyisobutyrate is allowed to run the maximum rate of this apparatus (0.04 molar unitsthour). Figures 1 and 2 show the separation of the fission prod-
I I
O P T I M U M ELUTION (PRECIPITATEI
IO?
c
zr
L
O0
4
8
I2
16
20
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28
TIME (HOURS1
Figure 1 . Optimum elution of earth activities with carriers
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ANALYTICAL CHEMISTRY
rare
hydroxyisobutyrate in the upper flask; about 800 ml. of t,he 0.1N solution and
Figure 2. Optimum elution of carrier quantities of rare earths
uct rare earths when the conditions are optimum as described in the procedure. Samples of yttrium, terbium, europium, samarium, and neodymium were counted for several half-lives with no apparent contamination present. Gadolinium precipitates, containing no Gd activity, were checked on the counters and found to contain no greater than O . O l ~ o contamination for Y and/or Tb. DISCUSSION
During this investigation the effects of changing mesh sizes and cross linkages of Dowex-50 were studied. Direct comparison tests showed that the cross 12 linkage resins give greater separation between elements hut that the time intervals were of the order of three to four times as long as with cross 8 linkage resins (Figure 3). By decreasing the size of the particles, we again observed increased separation of the elements at the expense of time, increased flow rate, and/or increased molarity of the eluants; conversely, increased resin particle size did not give adequate
RELATIVE ELUTION TIME
__ x-8
DOWEX 50 RESINS
Nancy Sawley and Alice Conover and for the invaluable aid given by Walter E. Nervik. LITERATURE CITED ( 1 ) Myatt, E., Nash, N., Jones, T., et al.,
NO OF TUBES
Figure 3. Comparative elution of some rare earths with Dowex-50-X 8 and -X 12 resins
separations under the conditions of the experiments. We believe that by the use of Dowex-50-X 8 100-200 mesh cation exchange resin and using the procedure described, we have achieved an optimum separation of the rare earths (Y, Tb, Gd, Eu, Sm, and Nd) with minimum time. ACKNOWLEDGMENT
The author is grateful for the assistance in -pray counting given by
McClellan Central Laboratory, USAF, 1963. private communication. (2) Nervik, W. E., J . Phys. Chem. 59, 690 (1955). (3) Quill, L. L., Rodden, C. J., “Scandium, Yttrium and the Rare Earths,” in “Analytical Chemistry of the Manhattan Project,” C. J. Rodden, ed., McGraw-Hill, New York, 1950. (4)Smith, H. L., Hoffman, D. C., J. Znorg. Nucl. Chem. 3, 243 (1956). (5) \ , Stevenson. P. C.. Nervik. W. E.. “The Radiochemistry of the Rare Earths, Scandium, Yttrium and Actinium,” NAS-NS 3020, Office of Technical Services, Washington, D. C. (1961). (6) Wolfsberg, K., “Determination of Rare Earths by Ion Exchange at Room Temperature,’] Los Alamos Scientific Laboratory, University of California, Los Alamos, N. M., 1963.
RECEIVEDfor review October 26, 1964. Accepted February 1, 1965. This work was performed under the auspices of the U. S. Atomic Energy Commission.
Gas Chromatographic Analysis of Products from Controlled Application of Heat to Paper and Levoglucosan SEYMOUR GLASSNER and A. R. PIERCE 111 Si. Regis Technical Center, Route 59A, West Nyack, N. Y . A small oven has been attached directly to a gas chromatograph SO that the volatile products from the thermal degradation of cellulose may b e analyzed without intermediate trapping. The application of heat has been controlled over a temperature range of 170” to 360’ C. for various periods of time. The close similarity of the volatile products from levoglucosan and cellulose, as found by direct analysis, adds to and confirms the data reported in the literature. The new evidence also supports the mechanism of degradation as postulated by earlier investigators that most of the thermal degradation producing the volatile compounds proceeds through levoglucosan.
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PAST 20 years considerable effort has been expended to determine the mechanism of the thermal degradation of cellulose, of cellulose derivatives, and of cellulose treated with flame retardant compounds. However, more than 100 years ago, GayN THE
Lussac (2) postulated a theory to support the flame retardancy of watersoluble salts-namely, that the flame retardant is decomposed by heat to form a glass-like coating on the individual fibers. The coating in turn serves as a barrier against the flame and oxygen from the air, and the highly flammable tars of decomposition become entrapped in this solid foam and are inhibited from further combustion reac t,ions. I n 1955 Esteve and coworkers (6) advanced the theory of the degradation of cellulose through a n intermediate, levoglucosan, a n anhydromonosaccharide, which subsequently undergoes two competing reactions: further degradation to flammable, volatile lower molecular weight compounds and tar, and repolymerization and aromatization to form char. It had previously been shown that flammability was related to the amount of tar and volatile materials produced (1, 7 , 8,12). Schwenker and Pacsu (IO)working on the tarry fraction from cellulose pyrolysis found water and levoglucosan to be
the major components; levoglucosan content was about 12%. They proposed that the cellulose might be chemically modified so as to inhibit the formation of the levoglucosan (6). Schwenker and Beck (9) studied the volatile products from the pyrolysis of cellulose by gas chromatography in order to further elucidate the mechanism involved. They found some 37 volatile products. I n conjunction with an investigation into the thermal stability of paperboard, it was thought worthwhile to study the volatiles of levoglucosan in comparison with cellulose to further clarify the degradation mechanism. The purpose of this work was to determine the extent of degradation in terms of various heating conditions in order to develop paper and paperboard with It was improved thermal stability. desirable therefore, to correlate the volatile products from the thermal degradation of paper with the parameters of temperature and time. A valuable tool might be developed for the analysis of additives that cannot be VOL. 37, NO. 4, APRIL 1965
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