The method should also prove valuable in the purification and isolation of neptunium. Potential Uses in Hydrometallurgical Processes. The separations technologist should find profitable applications for this method to nuclear fuel reprocessing and the recovery of uranium from ores. The extraction of uranium and plutonium from acetate solution with long-chain tertiary amines appears t o be more highly selective than current processes utilizing nitrate, sulfate, or chloride solutions. The reagents described in this paper are inexpensive and readily available. Because no solid salting agents are required, waste disposal is
simplified. A major advantage is the essentially noncorrosive nature of the acetate system when compared with the nitric, sulfuric, hydrochloric, and hydrofluoric acid processes now used. The selective leaching of uranium from hydrous oxides or other solids with acetic acid or ammonium acetate solutions to give liquors directly amenable to liquid-liquid extraction with amines would appear to offer a profitable avenue to the uranium processor. ACKNOWLEDGMENT
The author gratefully acknowledges the capable assistance of G. R. Wilson
and staff in performing some of the analyses. LITERATURE CITED
(1) . , Ahrland. S., Scta Chem. Scand. 5, 199 (i95ij. (2) Brown, K. B., Coleman, C. F., Cmnse. D. J.. Denis. J. 0.. Moore. _..__. J. G., U. S. Atomic Eneigy Comm. Rept: ORNL-1734 (May 27, 1954). (3) ~. Moore, F. L., ASAL. CHEST.29, 1660 (1957). (4) Ibid., 30, 908 (1958). ( 5 ) Sheppard, J. C., U. S. Atomic Energy Comm. Declassified Rept., HW-51958 (Aug. 8, 1957). RECEIVED for review January 25, 1960. Accepted May 6, 1960. llivision of Analytical Chemistry, 136th Meeting, ACS, Atlantic City, S . J., September 1959. '
Determination of Fission Product Iodine Cation Exchange Purification and Heterogeneous Isotopic Exchange WILLIAM J. MAECK and JAMES E. REIN Atomic Energy Division, Phillips Petroleum Co., Idaho Falls, Idaho
)This method for the determination of radioiodine in fission product mixtures i s based on separation of other activities by cation exchange, followed by heterogeneous isotopic exchange of iodide. Over-all recovery is 97.170 with a coefficient of variation of 3.1 when standard iodine-131 is used. Precision based on replicate determinations of iodine-1 3 1 in 14-day-old fission product samples is 3.6% coefficient of variation. A major advantage of the method i s that no yield determination is required.
70
T
classical carbon tetrachloride extraction method (2) for the separation and determination of radioiodine in fission product mixtures has been used routinely in this laboratory for several years. Although results have been adequate, a shorter and less involved method seemed desirable. Generally, simple heterogeneous isotopic exchange reactions are fast and specific (8); however, they have seldom been used in radiochemical analytical methods. Sunderman and Meinke (7) have reviewed procedures using this technique and successfully applied it to the determination of radiosilver. They showed the reaction HE
Preformed silver iodide has been studied for removal of iodine from Hanford stack gases by heterogeneous exchange ( 4 ) . An exchange reaction of active iodine with preformed silver iodide has been applied to the determination of radioiodine in reactor water with about 85% yield ( 5 ) . The incomplete yield may be due to adsorption of iodine on the lanthanum hydroxide used as a scavenger for other fission products ( 7 ) . Initial experiments showed that direct contact of preformed silver iodide with gross fission products gave a precipitate contaminated with fission product cerium and zirconium or niobium. Because scavengers such as lanthanum and ferric hydroxide tend to carry iodine (7), another means of separating these fission products was sought. Cation exchange appeared to be the simplest technique and was seA successful lected for evaluation. method was developed involving cation exchange separation of gross fission product activity followed by isotopic exchange of radioiodine on preformed silver iodide. The method is virtually quantitative; hence, yield determinations are not required. APPARATUS
A 3 X 3 inch NaI(T1) scintillation t o be complete in 15 minutes and the
precipitate to be essentially free of foreign activity. Sunderman (6) using this technique for separating iodine-I31 reported erratic results.
crystal coupled to a 256-channel Radiation Counter Laboratory pulse height analyzer was used for all counting. Precipitates were collected on 25-mm. Rlillipore filters, Type pH, pore size of 0.30 micron, and mounted on 3 X 4
inch aluminum plates. The 1 X 20 cm. ion exchange column was fabricated from a cut-down 25-ml. buret. REAGENTS
ilnalytical grade reagents were used throughout, except for the 5% sodium hypochlorite, which was commercial grade Clorox. Exchange resin, Domex 50-X8, 100200 mesh. Silica gel. Iodine-131, Isotopes Division, Oak Ridge National Laboratorv. FTssion product mixturks were prepared by irradiating highly enriched uranium in the Materials Testing Reactor. PROCEDURE
Pipet a I-ml. sample into a 10-ml. beaker and make alkaline with an excess of 1M sodium carbonate. Add 1 ml. of 5% sodium hypochlorite and place under a heat lamp for 5 to 10 minutes. Acidify with a few drops of concentrated hydrochloric acid and add 2 ml. of 1M sodium bisulfite. Continue heating until the free chlorine is expelled, then cool. Prepare the ion exchange column by adding 5 to 6 ml. of resin t o the buret, which has a plug of glass wool a t the bottom. Wash with 20 ml. of 10N hydrochloric acid, then with water, and finally with 25 ml. of 0.01M sodium bisulfite-0. I N hydrochloric acid. Add 1 ml. of silica gel to the top of the column. While the sample is cooling, prepare the preformed silver iodide by adding 2 ml. of 0.05M potassium iodide to a 100-ml. beaker containing 1.5 ml. of 1N nitric acid. Add 3 ml. of 0.1N silver VOL. 32, N O . 9, AUGUST 1960
1079
nitrate, stir until the precipitate coagulates, then allow it to settle. Decant the supernate and wash twice with 10ml. portions of 1N nitric acid. Decant the final wash and add 10 ml. of 0.5M sodium fluoride. Small losses of the precipitate by decantation do not affect either accuracy or precision. Place the beaker on a magnetic stirrer under the ion exchange column. Place the sample on top of the column and elute with 10 t o 15 ml. of a 0.01M sodium bisulfite0.1N hydrochloric acid mixture a t a rate of 1 ml. per minute. Let the column effluent fall directly into the beaker of preformed silver iodide, which should be continuously stirred. After elution, continue to st,ir for 10 to 15 minutes. Filter through the Millipore filter, wash with a minimum amount of 0.1N nitric acid, and suck dry with vacuum. Mount the filter and count, preferably with a multichannel analyzer. DISCUSSION AND RESULTS
The heterogeneous isotopic exchange reaction is rapid and complete, if all the AgI
+ *I-
*
AgI
+ I-
radioiodine is present as iodide (8). Any oxygcnated species such as iodate or periodate in which more than a single electron transfer is involved exchanges slowly 10,001
’
M099-Tc99
8,00( 6,001 4,001
Tell‘
2,oo
1,001
or not at all (8). That fission product iodine exists in a multitude of oxidation states has been well established (9, 8). Hence, oxidation-reduction treatment is necessary. By oxidizing t o periodate followed by reduction to iodide, all oxidation states are covered. Hypochlorite in alkaline media followed by bisulfite in acid media has been used (2). The alkaline hypochlorite oxidation step was studied. With sodium hydroxide as the base as much as 20% of carrier-free iodine was lost. Both SOdium carbonate and ammonium hydroxide gave 100% recovery. The exact cause for this was not established. It may be that the more basic sodium hydroxide system either decreased the oxidation rate such that the zero valence (free iodine) volatile state existed for longer periods or that some type of volatile interhalogen compound was formed. It was confirmed that bisulfite reduces periodate to the iodide, which passes through the cation exchange column and easily exchanges vith the preformed silver iodide. The distribution of 14-day-old fission products in each step of the method is shown in Figure 1. Major activities passing through the ion exchange column other than iodine are molybdenum-99, technetium-99, and tellurium-132. Experimental work with aged fission products showed small amounts of antimony-125, ruthenium-103-106, 2nd zirconium-95 or niobium-95 also passing through the column. Ruthenium probably exists as an anionic chloride complex and the zirconium or niobium as hydrolyzed or colloidal species. Placing silica gel on top of the resin adsorbs additional zirconiumniobium (1). Of the activities passing through the ion exchange-silica gel
column, only a small amount of zirconium-niobium absorbs on the preformed silver iodide. This is adequately decreased by making the isotopic exchange in the presence of a large concentration of fluoride. Six aliquots of an iodine-131 standard were carried through the procedure. The recovery associated with the oxidation-reduction and ion exchange steps was 98.8% with a coefficient of variation of 0.9%. With a 15-minute contact with the preformed silver iodide, the over-all recovery was 97.1% with a coefficient of variation of 3.1%. Six aliquots of a 14-day fission product solution were also carried through the procedure. After mounting, the plates were allowed to stand 2 days before counting, so that short-lived iodine-132 could die out for easier evaluation of the gamma spectrum. A clean separation is shown by Figure 1, in which the precipitate is free of all activities except iodine-131. The coefficient of variation based on these six analyses v a s 3.6%. The majority of radiochemical methods include yield determinations mostly based on precipitation reactions. These are subject to such errors as coprecipitation and adsorption. Sunderman and hIeinke (?‘) give examples of the degree of contamination which can occur. If yield determinations must be made, such teckniques a s spectrophotometry or addition of an isotopic tracer should be superior, with the added advantage that liquid samples are easily counted in welltype scintillation counters. Radiochemical methods in which quantitative recovery is obtained both avoid questionable yield determinations and are faster.
80
LITERATURE CITED
60
D.. U. S. At. Enern, -“ Comm.,. Rept. Jener-57 (1958). (2) Glendenin, L. E., RIetcalf, R. P., paper 278 in “Radiochemical Studies. The Fission Products, Book 3,” C. D. Coryell and N. Sugarman, e&., Sational Nuclear Energy Series, Dlv. IS’, Vol 9 . %lcGrsu;-Hill.Ken. York. 1951. (3) GleGdenin, L. E ,’ lletcnlf, R. P., Kovey, T. B., Coryell, C. D., Ibzd., paper 279. (4) McClanahan, E. D., U. S.At. Energy Comm., Rept. HW-47676 (1956). 15’1 McIssac, L. B., Westinahowe Electric Cord.. oriimte communication, April 195b.’ (6) Sundermnn, D. X., U. S. At. Energy AECU-3159 C U - 3 1 5 9 (1956). 119:i6 1. Comm., Rept. U ((7) 7 ) Sunderman, D. Y., hleinke, hleinlte, ST ST.. IT., ANAL. CHEM.29, 15% (1957). (8) Wahl, A. C., C., Bonner, S . A., “RadioChap. activity Applied to Chemistry,” Chemistry, ” Chap 1, Wiley, New York, 1951. RECEIVF~D for revien. January 2 5 , 1960. Accepted May 20, 1960. Division of Analytical Chemistry, 136th Meeting, ACS, Atlantic City, X . J., September 1959. Work supported by the U. S. Atomic Energy Commission under Con. tract AT(10-1)-205.
(1) Cvietranin. \ - I
40 t
t 2
COLLMN EFFLUENT
I-
::20( W
2
tl d a
101 8C
\ - ,
6C 4c
2 DAYS AFTER
2c
IO
IO
Figure 1.
1080
20
30
40
60 70 80 90 100 110 120 130 140 C H A N N E L NO. (12.5KEVICHANNEL) 50
Distribution of 14-day cooled fission product in method
ANALYTICAL CHEMISTRY
