LITERATURE CITED
(1) Barnard, A. J., Broad, W. C., Flaschka, H., The EDTA Titration:
LVature and Methods of End Point Detection, J. T. Baker Chemical Co., Phillipsburg, N. J., November 1957. (2) Blaedel, W.J., Knight, H. T., ANAL. CHEM.26. 741 (1954). (3)-Blaedel,'W. J,, Laessig, R. H., Zbid., 36, 1617 (1964). (4) Blaedel, W. J., Olson, C. L., J . Chem. Educ. 40, A549 (1963). ( 5 ) Blaedel. W.J., Olson, C. L., Sharma, L. R., ANAL. CHEM.35, 2100 (1963). (6) Blaedel, W. J., Strohl, J. H., Zbid., 37, 64 (1965). (7) Fritz, J. S., Richard, AI. J., Karraker, S.K.. Ibid.. 30. 1347 (1958). (8) Haslam, J., Squirrell, D. C. M., Blackwell, I. G., Analyst 85, 27 (1960). ~
I
,
(9) Khalifa, H., Patzak, R., Doppler, G., Z. Anal. Chem. 161, 264 (19.58). (10) Kolthoff, I. M., Yerzyl, E. J. A. H., Rec. Trav. Chem. 42, 1055 (1923). (11) Polcen, J., Chem.Listy 51,168 (1957); CCCC 22, 1057 (1957). (12) Ramaley, L., Brubaker, R. L., Enke, C. G., ANAL.CHEM.35, 1088 (1963). (13) Reilley, C. N., XVth International Congrees, Anal. Chem., Lisbon, 1956, Abstract p. 187; Scientific Apparatus and Xethods (E. H. Sargent Co.) 9, 15 (1957). (14) Reilley, C. N., Schmidt, R. W., ANAL.CHEW30, 947 (1958). (15) Zbid., p. 953. (16) Reilley, C. N., Schmidt, R. W., J . Am. Chem. SOC. 78, 1513 2910, i 1956). (17) Ringbom, A,, J . Chem. Educ. 35, 238 (1958). \ - - - - I
(18) Ringbom, A , , Treatise on Analytical Chemistry, Interscience Encyclopedia Inc., I. AT. Kolthoff, P. J. Elving, eds., Volume 1, p. 608, Sew York, 1959. (19) Schmidt, R. W., Chemist Analyst 51, 56 (1962). (20) Schoenbaum, R. C., Breckland, E., Talanta 11, 659 (1964). (21) Schwarzenbach, G., Anderegg, G., Helv. Cham. Acta. 37, 1289 (1954). (22) Schwarzenbach, G., Freitag, E., Zbzd., 34, 1503 (19511. (23) Siggia, S.,Eichlen, D. R., Rheinhart, R., ANAL.CHEW27, 1745 (1955).
RECEIVED for review December 3, 1964. Accepted January 4, 1965. \Vork supported by Grant No. AT(11-1)-1082 from the Atomic Energy Commission.
Controlled- Potentia I Cou Io metric Titration of Uranium(V1) in Aqueous Solutions of Sodium Fluoride W. R. MOUNTCASTLE, Jr.,l LOUISE B. DUNLAP, and P. F. THOMASON Analytical Chemisfry Division, Oak Ridge Nafional laboratory, Oak Ridge, Tenn.
b A method has been developed for the controlled-potential coulometric titration of U(VI) in aqueous solutions of NaF. The method involves the coulometric reduction of U(VI) to U(IV) a t - 1 .OOO volt VE. S.C.E. in neutral or slightly acid 0.75M NaF. The relative standard deviation is no greater than 0.5%; the relative error is +0.2 to +0.3% a t the 6-mg. level. Reasonable amounts of Cr(lll), Cu(ll), Mo(VI), and Zr(lV) do not interfere. Mole ratios a t least as large as 1 : 1 for Fe(lll) to U(VI) and 5:l for AI(III) to U(VI) can b e tolerated. The method was applied to a number of synthetic reactor-fuel dissolver solutions.
R
complex fuel elements contain a number of alloying elements,-for example, zirconium, molybdenum, nickel, iron, chromium, and aluminum. New methods are thus required for the determination of uranium in various types of the highly radioactive spent fuel elements. Controlled-potential coulometric titrations are especially adaptable to remote manipulator-type operations. At the Oak Ridge National Laboratory, U(V1) is determined routinely by controlled-potential coulometric titration in 0.5M H2S04 (8);Fe(III), l l o ( V I ) , and other cations interfere when present in more than trace amounts. Zittel and ECENTLY DEVELOPED
1 Present address, BirminghamSouthern College, Birmingham 4, Ala.
336
*
ANALYTICAL CHEMISTRY
associates (12, I S ) developed methods in which sodium tripolyphosphate (NasP301a) is the supporting electrolyte; these methods permit the determination of U(V1) in the presence of large amounts of Mo(V1) and small amounts of Fe(III), Th(IV), and other cations. Shults and Dunlap (9) developed a trin-octylphosphine oxide estraction procedure that isolates U(V1) from a number of interfering cations. Subsequently, U(V1) is determined by controlled-potential coulometric titration in 0.5J1 H2S04. Booman and Holbrook ( 2 ) investigated other procedures for extracting U(V1) and titrating it coulometrically. Verbeek, Moelwyn-Hughes, and Verdier (11) describe a polarographic method for U(V1) that can tolerate excess Fe(I1I); the supporting medium is neutral 0.75M NaF. Two waves exist; the first (E,,? = -0.65 volt us. S.C.E.) coalesces with the second ( E l l z = -0.95 volt us. S.C.E.). Consequently, the height of the composite wave is used to determine the diffusion current. Because the reactions that occur in polarography and controlled-potential coulometric titrimetry are similar, it was decided to evaluate sodium fluoride as a supporting electrolyte for coulometric titrimetry. The reduction of U(V1) in neutral (or slightly acid) solutions of S a F was studied. Conditions were established for the quantitative controlled-potential coulometric reduction of U(V1) in aqueous solutions of XaF. Possible interferences were checked, and the precision and accuracy of the method were determined. The method was
applied with various degrees of success to a number of typical synthetic, reactor-fuel dissolver solutions. These studies did not include the effects of fission products of radiation. EXPERIMENTAL
Apparatus. Coulometric Titrator, ORKL Model Q-2005, controlledpotential ( 7 ) ; used for all coulometric studies. The calibration, use, and care of this instrument are described (6). A mechanically stirred mercury cathode and a saturated calomel reference electrode (S.C.E.) were used in a conventional coulometric cell (8). The Vycor tubes, which are normally used as membranes and which contain the platinum wire or counter electrode and the S.C.E., were replaced by fritted tubes that contained a 3yo (w./v.) agar5Yo (W./V.) KiSO, plug (1s). pH Meter, Beckman Model G ; used to measure the p H of the solutions to be titrated. Reagents. Supporting Solutions of Sodium Fluoride; prepared from analytical-reagent grade sodium fluoride. After addition of the prepared test portions to these media, p H adjustments were made with 3070 (w./v.) solution of XaOH. A11 other reagents used in the preparation of t h e test portions were ACS-approved grade. Standard Solutions of U(V1); prepared by dissolving portions of Xational Bureau of Standards standard sample KO. 950 U30s in -7.551 HXO-, destroying the nitrate by fuming with H2S04$ and diluting the resulting solution to volume with 0.5.11 H2S04. The final solution was standardized volumetrically by potentiometric ti-
I
1
I
i
solution a t -0.210 volt us. S.C.E. Coulometrically reduce TJ(V1) to U(1V) at -1.000 volt us. S.C.E. until the current again decreases to 50 pa. Via Faraday's laws (n = 2) and from the readout voltage of the integrator, calculate the amount of U(V1) titrated. RESULTS AND DISCUSSION
Choice of Titration Conditions. Curves are given in Figures 1, 2, and 3 t h a t relate readout voltage, which is a measure of the quantity of current consumed during electrolysis, with controlled electrode potential when U(V1) is reduced electrolytically in several supporting media. D a t a for these curves were obtained by making the reduction in the usual manner except t h a t periodically throughout t h e electrolysis the potential was E VI S.C.E., volt adjusted to a value which caused cessation of current. The readout voltage Figure 1 . Effect of NaF concentration (proportional to current consumed or on coulometric reduction of U(VI)extent of reaction) and electrode potenU(IW tial were recorded, and the electrolysis (5.66 mg. of U(Vl), 10 ml. of electrolyte, pH = 71 was then continued. Curves plotted A 0.50M NaF from a series of such data are especially 0.75M NaF useful in comparing supporting media 0 1.00M NaF with each other and in establishing optimum electrode potentials, because tration with standard ferric sulfate they relate extent of reaction with solution (4). electrode potential under actual titraProcedure. Preparation of T e s t tion conditions. Portion for Titration. I n t o a 50-ml. Uranium(V1) in a n aqueous solution Vycor beaker t h a t contains 5 ml. of of N a F can be reduced electrolytically 3 M H 2 S 0 4 , pipet from t h e sample a a t a mercury cathode; a 2-electron test portion t h a t is estimated to contain about 6 mg. of U(V1). change occurs during the overall reAdd 5 drops of concentrated "03. duction. As the curves in Figure 1 Evaporate the solution to near dryness; indicate, the potential of the U(V1) do not bake the residue. After the -+ U(1V) reduction varies considerably residue is cool, add sufficient 5y0(w./v. with change in N a F concentration. The hydroxylamine hydrochloride (-5 same curves also show that the potential drops) to reduce Cr(V1) to Cr(II1). of the U(V1) + U(1V) reduction in Transfer the solution to the titration 0.50.11 N a F is very close to the reduction vessel, using a wash of 0.75J1 N a F ; use potential of C02+* in acid media a total volume of 10 ml. of the N a F solution to effect the transfer. Add 3 (-0.325 volt us. S.C.E. in 0 . 5 X H2S04) drops of a saturated solution of sulfamic ( 8 ) . Fluoride ion in concentration acid. Add dropwise 3oy0 (w./v:) greater than 0.50J1 is required to avoid NaOH until the color of the basic premature reduction of U(V1). The U j V I ) , which appears after the addition for 0.75-Lf and 1.OOM X a F concurves of each drop, persists but disappears in firm this observation. I n 1,OOM S a F , 15 to 30 seconds; avoid an excess of the L-(VI) + U(1V) reduction appears reagent. Using a pH meter, adjust to be slower and to require a more the p H to the value between 6.5 and negative reduction potential for the 7.0 with I.0JI S a O H and/or 0.5M H2S04. (The suitability of p H buffer complete electrolytic reduction of U(V1) solutions was not studied.) EXCEP- than in 0.7551 K a F . Interference from TION: When Cu(I1) and/or large the reduction of hydrogen ion could amounts of Al(II1) (-5 mg.) and result. Fe(II1) (-20 mg.) are present, adjust Figure 2 indicates that U(V1) can be the pH to 5.5. Wash the electrodes reduced in 0.75M N a F over the p H of the pH meter with a minimum range from 5.5 to 7.0 without significant amount of 0.7551 NaF. loss in current efficiency. However, Coulometric Titration of U(V1). Add practical as well as theoretical con7.5 ml. of mercury to the titration cell, place the cell in position, and sparge siderations dictate that the pH be conthe solution 5 minutes with a brisk trolled carefully. At pH 6 or lower the stream of helium. Maintain a helium electrolytic cell is attacked by hydroblanket over the test solution during fluoric acid. Even in neutral or slightly the following electrolysis. Prereduce acid media, the Vycor tubes specified in the solution a t -0.300 volt us. S.C.E. the conventional cell assembly are stable until the current decreases to 50 pa.; then zero the integrator. EXCEPTION: for only two or three days. Under the same conditions, fritted glass tubes are When Cu(I1) is present, prereduce the
E vs S.C.E., v o l t
Figure 2. Effect of pH on coulometric reduction of U(VI)-U(IV) in 0.75M NaF [5.59 ml. of U(VI), 10 rnl. of 0.75M NaF] 0 pH 7.0 A pH 5.5
satisfactory for six weeks to several months. However, at pH 7.0 and coprecipitates with Fe (111) and AI(II1) a t p H 0.2M Fe(III), >0.5M
Table IV.
Al(III), or trace amounts of Mo(V1) (18). The method is applicable for the determination of U(V1) in the following dissolver solutions: Consumer Public Power Reactor, Experimental Boiling Water Reactor, Fermi Reactor, and Molten Salt Reactor. The method can be used for the approximate determination of U(V1) in dissolver solutions of the Foreign Research Reactor type, 14
Results of Coulometric Titration of U(VI) in 0.75M NaF in Presence of Various Synthetic Dissolver Solutions
Aliquots of U(V1) solution added to dissolver solution and sample titrated by procedure given Av.
U(VI), mg. Taken Found
3.34 6.05 6.42 6.67 12,09
3.34 6.04 6.44 6.68 12.09
3.34 6.05 9.07c 9.07d
3.37 6.06 9.03 9.02
9.07
8.92
3.49 5.00 6.17 6.67 12,09
3.48 5.10 6.19 6.73 12.07
9.07
9.14
3.34 6.05 9.07 12.09
3.3 6.01 8.84 11.90
3.00 6.39 8.04
3.05 6.37 8.00
Rel. std. Rel. error, % Xa dev., 70 CONSUMER PEBLIC POWER (1 ml., 1:25*) 0.22 0.00 7 0 15 -0 17 8 0.28 $0.31 9 0.49 +0 15 11 0.37 0.00 14 EXPERIMENTAL BOILING WATER (1 ml., l:lb) 0.72 +0.89 7 0.70 0.17 5 0.40 -0.44 9 1,90 -0.55 6 (1ml., no dilutions) 1.07 -1.66 8 FERMI (1 ml. l:5Ob) 1.52 -0.29 7 0.65 +2.00 5 0.36 +0.32 5 0.72 10.78 8 0.26 -0.17 17 (2ml., 1:50b) 4 0.30 +O. 77 FOREIGN RESEARCH (1ml., 1 : l b ) 17 0 4 1.32 -0,65 5 3.2 -1.4 5 2.0 -1.7 7 MOLTENSALT (5ml., 0.2Min molten salt) 1.66 +1.66 1.59 -0.30 0.38 -0.50
6 5 5
time/ titration PH
min.
6.8 6.9 7.0 6.9 6.7
23 30 27 45 45
6.7 6.7 6.8 6.8
21 32 25 40
6.7
49
6.9 7.0 6.9 6.7 6.6
33 25 36 36 41
7.0
35
4.8 4.5 5.5 4.5
35 50
6.7 6.7 6.5
32 36 42
55
38
(5 ml., 0.2Min molten salt, 0.15mmole of NaF added)
3.05
3.12
0.33
f2.0 5 . s. SAVAXNAH' (1 ml., 1:20b) 1.20 -0.60 1.16 0.00
3.34 3.32 6.67 6.67 S = number of titrations. * Designates v./v. dilqtion. c Cell resistance less than 4000 ohms; see text. d Cell resistance greater than 10,000ohms; see text. e Careful prereduction of Cr(T1) required, see text,
5
6.5
30
6 6
5.7 5.6
40 40
VOL. 37, NO. 3, MARCH 1965
339
mg. of Al(II1) per 7 mg. of U(VI), and the N . S . Savannah type. The latter’s combination of interferences due to mole ratios of 0.7:l for Cr(II1) to U(VI), 1 . 5 : l for Fe(II1) to U(VI), and 0.3:1 for Ni(I1) to U(V1) in its dissolver solution demands very exact pretreatment of the sample to minimize their combined effects. Dissolver solutions of the d r m y Package Power Reactor type, which contain a 4 0 : l mole ratio of Fe(II1) to U(VI), and of the Consolidated Edison Reactor type, which contain a 17 : 1 mole ratio of Th(1V) to U(VI), were not amenable to the method. I n the latter solution, Th(1V) interferes in the 3M H2S04 with fuming by precipitating as Th(S04)2; when the 0.75M N a F is added, it interferes by precipitating as ThF4. This investigation indicates the need for the development of a cell assembly that withstands acid fluoride solution. Also, there is need for a supporting medium from which Fe(II1) and Al(II1)
do not precipitate. The medium Na6p3010 (6y0 w./v.)-NaF (sat.) was examined briefly; it appears to be promising. LITERATURE CITED
(1) Biggs, R. B., “Molten-Salt Reactor
Program, Semiannual Prog. Rept. for Period Ending Jan. 31, 1963,” U . S .
At. Energy Comm. Rept. ORNL-3419,
p. 127 (May 24, 1963). (2) G. L.. Holbrook.’ W. B.. \ , Booman. AXAL.~ H E M 31, . i 0 (1959). (3) Booman, G. L., Holbrook, W. B., Rein, J. E., Ibid., 29, 219 (1957). (4) Ginocchio, B. J., “Uranium, Automatic Potentiometric Ferric Sulfate Method,” Method Nos. 1 219224 and 9 00719224 (2-24-58); ORNL Master Analytical Manual, U . S . 9 t . Energy Comm. Rept. TID-7015, Sec. April 1958. (5) Goldstein, Gerald, ANAL.CHEM.36, 243 (1964). (6) Jones, H. C., “Automatic Coulometric Titrator, ORKL RZodel Q-2005, Electronic, Controlled - Potential,” Method Nos. 1 003029 and 9 003029 (R. 6-7-62); ORNL Master Analytzcal
Manual, U . S.At. Energy Comm. Rept. TID-7015, Suppl. 4, June 1962. ( 7 ) Kellev. R l . T.. Jones, H. C.. Fisher. D. J., A ~ A LCHEM. . 31 ,’488, 956 (1959):
(8) Shults, W. D., “Uranium, Automatic Controlled - Potential Coulometric *Method,” Method Nos. 1219225 and 9 00719225 (1-29-60); ORNL Master Analytical Manual, U . S. At. Energy Comm. Rept. TID-7015, Suppl. 3 June 1961. (9) Shults, W. D., Dunlap, L. B., Anal. Chim. Acta, 29, 254 (1963). (10) U.S. At. Energy Comm., “Proceedings of the AEC Symposium for Chemical Processing of Irradiated Fuels from Power, Test, and Research Reactors, Richland, Washington, October 20 and 21, 1959,” TID-7583, January 1960. (11) S’erheek. A. A,. Moelwvn-Hughes. ’ J: T., Verdier, E. T . , Anal. ?him. acta; 22, 570 (1960). (12) Zittel, H. E., Dunlap, L. B., A x . 4 ~ . CHEM.35, 125 (1963). (13) Zittel, H . E., Dunlap, L. B., Thomason, P. F., Zbid., 33, 1491 (1961). RECEIVEDfor review October 1, 1964. Accepted December 18, 1964. Research sponsored by the U. S. Atomic Energy Commission under contract with the Union Carbide Corp.
Determination of Uranium and Americium-Curium in Urine by Liquid Ion Exchange F. E. BUTLER Savannah River Planf, E. I. du Ponf de Nemours and Co., Aiken, S. C.
b Exchange of Th, Pa, U, Np, Pu, Am, Cm, and Cf from various concentrations of “ 0 3 and HCI to liquid ion exchangers was determined. Both anion and cation exchangers were used; the former was triisooctylamine (TIOA), while the latter was di-2ethylhexyl phosphoric acid (HDEHP). Tests with TIOA indicated preferential and rapid removal of U from other actinides, and in a mixture of Pu(lll) and Np(lV), N p was extracted to TIOA. The reagent also separated Pa233 from the parent NpZ3’. HDEHP extracted more than 90% of all eight actinides from an acid solution adjusted in the pH range 4 to 5. At higher acidities-e.g., 4N “ 0 8 all the actinides are extracted except Am, Cm, and Cf. Procedures were developed for analysis of U235and Am241-Cm244 in urine. Tracer recoveries were greater than 90% and decontamination factors were sufficiently high for other actinides. Detection limits by direct alpha counting were 0.3 d.p.m. for 250-mi. urine samples. Overall recoveries, through electrodeposition techniques, were 84 2 10% for UZ3jand 89 5 6% for Am241. 340
ANALYTICAL CHEMISTRY
A
to determine actinides separately and as mixtures are needed more as production of transplutonium elements increases. Liquid ion exchange is a relatively new technique for chemical analysis. With this technique, an aqueous sample and organic reagent dissolved in an inert solvent are thoroughly mixed. Xuclides as anions and cations are substituted at exchange sites in the immiscible organic phase, in a manner similar to absorption by solid ion exchangers (3, 4 ) . An advantage is the rapidity of both absorption and desorption of ions. A survey of the literature showed limited use of liquid ion exchange for analytical procedures, particularly for analysis of actinides in urine. Previous tests at the Savannah River Plant with H D E H P resulted in a method to separate Ca and Sr ( 2 ) . This reagent and TIOA were further studied to develop analytical techniques for the actinides T h through Cm. NALYTICAL METHODS
I
EXPERIMENTAL
Reagents. H D E H P from Union Carbide Chemical Co. was purified by washing with 4 N H X 0 3 and water
prior to use. TIOA from Bram Chemical Co. was not purified before use. TIO.A-xylene, lo%, and H D E H P toluene, 20%, were satisfactory dilutions for the reagents, and are henceforth referred to as TIOA and H D E H P . For exchange reactions, equal volumes of organic and aqueous solutions were used unless otherwise specified. Procedure. Actinides were tested separately with the anion and cation exchangers. Ten-milliliter samples of individual actinides were shaken vigorously for 1 minute and allowed to settle. Small aliquots of the aqueous samples were counted for alpha and/or gamma activity before and after exchange. No attempt was made to adjust actinide valences initially. Each spike solution was evaporated to dryness with the same acid used for dissolution in the test. RESULTS
Anionic Complex Formation (TIOA). Results of initial tests with TIOA and aqueous solutions are summarized in Table I , including the probable valence of each actinide. Only U23*and Pa233were removed from
