Application of Ion Exchange to the Colorimetric Determination of Trace Amounts of Uranium Using Dibenzoylmethane SIR: A method for ion exchange separation and colorimetric determination of uranium is reported, an extension of previous work (5-5). The uranium, complexed with dibenzoylmethane in 80% alcohol, is determined colorinietrically a t 400 mp. This method has been routinely applied to a large number of low-grade uranium samples. EXPERIMENTAL
Reagents. Resins included Dowex 1, Dowex 2, Duolite A-101, and Amberlite IRA-400. ilmberlite IRA400, consisting of 40- to 60-mesh beads and purchased as Amberlite XE-117, Type 1 or 2 , is recommended. A standard uranium solution containing 50 mg. of uranium oxide per liter was prepared from uranyl sulfate. All other chemicals were of reagent grade. Apparatus. Absorption measurements were made with a Bausch & Lomb Spectronic 20 colorimeter with 0.5- and 1-inch cells. A Beckman Model G p H meter was used for p H control. A column similar to the one described (4, 6) was used, except that a 14/20 standard-taper ground-glass joint connected the dropping funnel and the column. Procedure. The procedure for dissolution of the ores and separation of uranium by ion exchange is essentially as reported (5-5). The perchloric acid eluate containing the uranium is collected in 400-ml. beakers, which are placed on an asbestos-covered hot plate regulated a t 250" to 300' and evaporated almost to dryness. The last traces of perchloric acid are removed by placing the beakers in a furnace regulated between 250' and 300" C. for 10 to 20 minutes. After cooling, the sides of the beakers are washed down with 10 ml. of distilled water and thoroughly policed, whereupon 25 ml. of 95% ethyl alcohol is added. One milliliter of a 1% solution of dibenzoylmethane in 95% alcohol is added and the solution brought to an apparent p H of 7.0 to 7.5 by regulation with O.OO5M sodium hydroxide or sulfuric acid. This solution is transferred to a 50-ml. volumetric flask with 9501, alcohol. The solutions are filtered through retentive filter paper such as Whatman KO.5 to remove traces of insoluble residue and absorbances are determined a t 400 mp. The blank is prepared from 1 ml. of 1% dibenzoylmethane in 50 ml. of 80% ethyl alcohol solution I
This procedure is satisfactory for nearly all types of uranium samples, including those containing thorium up to a thorium-uranium ratio of 5 to 1. If the thorium-uranium ratio is higher, it would be readily detected by abnormally high radiometric measurements. The procedure can be modified to handle samples containing up to 100 mg. of thorium by including a 100-ml. wash with 10N hydrochloric acid after the final wash with hot water and before elution with 1M perchloric acid. Excess water should be removed from the column before the hydrochloric acid wash. For samples containing more than 100 mg. of thorium or calcium phosphate the procedure was altered to include a double column separation. After solution of the ore, the sample is evaporated to dryness with hydrochloric acid, taken up in 50 ml. of IOM hydrochloric acid, and adsorbed on the chloride form of the resin. After the resin is washed with approximately 50 mi. of 10M hydrochloric acid, the sample is eluted with 100 ml. of hot 10% hydrochloric acid. Upon standing 10 minutes, the last of the eluate is blown out with air. Five milliliters of 9M sulfuric acid is added to the eluate, and it is evaporated to strong fumes.of sulfur trioxide. After cooling, 100 ml. of distilled water is added and the solution boiled until the residue dissolves. After the pH is adjusted to about 1.2, the sample is treated with 10 to 30 ml. of 6% sulfurous acid and readsorbed on the sulfate resin. Development. An investigation of anion exchange resins revealed t h a t Amberlite IRA-400 or Duolite A-101 was the most satisfactory for both the standard procedure and the double column separation. The Dowex 1 and Dowex 2 resins could be eluted satisfactorily with 10% hydrochloric acid, b u t only about half of the uranium was recovered with 1M perchloric acid. -4 number of other solvents can be substituted for ethyl alcohol. The most practical system investigated was isopropyl alcohol-water solutions limited between 50 and 807, alcohol. Because the colored complex had to be developed in a neutral solution, all the acid-eluting agent had to be eliminated before color development. Rel-
Table 1. Removal of Last Traces of Perchloric Acid before Color Development
[0.20 mg. of uranium (U308)present] Furnace Treat- Uranium Av. Temp., ment, Found, Dev., "C. Min. hlg. 250 30 0.20 0.000
a.
300
30
350
30
400
30
500
15
500,300"
15,30
0.20
0.000
0.20 0.20 0.175 0.180 0.173 0.185 0,148 0.105 0.20 0.20
0.000 0.000
-0.025 -0.015 -0.027 -0.020
-0.052 -0.095 0.000
0.000
a Sample 6 was heated for 15 minutes at 500' C., then redissolved, retreated with perchloric acid, and reheated for 30 minutes at 300" C .
atively small amounts of acid caused excessive salt formation in the alcohol system and gave low results. The bulk of the perchloric acid can be easily removed by evaporation on a hot plate in a perchloric acid hood. Early attempts a t removing the last traces of acid with a Bunsen flame gave erratic results, To explain this phenomenon, a series of experiments was performed, eliminating the last traces of perchloric acid in a controlled muffle furnace a t various temperatures (Table I). The temperature is critical, as elevated temperatures convert some of the uranium into an insoluble form. DISCUSSION A N D RESULTS
Interferences studied in addition to those previously reported (1, 4) were the effects of excessive amounts of thorium and calcium phosphate. I n sulfate solutions thorium formed an anionic complex that was adsorbed by the resin. Samples containing more than 2 mg. of thorium showed a considerable residue of thorium salts after evaporation of the eluate, the amount increasing with thorium concentration. Concentrations in excess of 1 mg. interfered in the absorbance readings. For concentrations between 1 and 100 VOL. 3 1 , NO. 5, M A Y 1959
957
LITERATURE CITED
Table 11.
Standard Samples Run by Routine Procedure
Actual yc
(UsOs) Weight
Reported Sample New Brunswick No. 1 (phosphate rock)
for
Standard 0,029
of
Sample, G. 1.00 1.oo
Dev.
% Us08 Found Duplicate analyses Av . 0.024 0.024 0.025 0,027" 0.0274
of BV.
from Reported Value -0 005
0,027
-0 002
0.180
0.000
0,110
-0 004
0.064
0 000
0.104
-0 005
0.00065
-0 00006
O.OOO75
0 00004
0.0148 0.0152
0,015
0 000
0.0178
0,018
-0 001
0.023
-0 001
0.012
OOOO
0.011
-0 001
AEC 4
0.180
0.20b
5
0.114
0.25b
8
0.064
1.00
9
0.109
0.25a
0.00071 (17.1 p.p.m.)
5.00
Rubidoux Mtn. leucogranite
10.00
0.180 0.180 0,110 0.109 0.063" 0.06E1~
0.104
0.104 0.0006 0.0007 0.0007 0.0008
(1.1 Fisher. S.. Kunin. R.. A s . 4 ~ .CHEY.
. 29, 400'(1957). ' ' (2) Kraus, K. A., Moore, G. E., Kelson, F., J. Am. Chem. SOC.78,2692 (1956). (3) Seim, H. J., Morris, R. J., U. S. Atomic Energy Comm. Rept. RMO2682 (1958). (4) Seim, H. J., Morris, R. J., Frew, D. IT.,ANAL.CHEM. 29, 443 (1987). ( 5 ) Seim, H. J., Morris, R. J., Frew, D. W., U. S. Atomic Energy Comm., Rept. RMO-2680 (1956).
H. J. SEN R. J. MORRIS R. G. PASTORINO
Department of Chemistry University of Nevada Reno, Nev. COZDUCTED under Contract KO.AT(491)-624 between the U. S. Atomic Energy Commission and the University of Yevada, Llackay School of Mines.
Natl. Lead 1
0.015
2
0,019
3
0.024
1.00
4
0.012
1.00
3
0.012
1.00
h c
1.00 F
1.oo
0,0182 0.0225 0.0230 0.0120
0.0116 0.0113 0.0110
F'alues obtained by double column technique. Aliquots of 1.00- or 1.25-gram samples. Sample dissolved using H F and "03.
nip. per sample, a 100-ml. wash of 10-Y hydrochloric acid after adsorption usually eliminates the interference. For concmtrations above 100 mg., the double coliimii separation is recommended; thorium would not be a problem even in pucessive amounts, as it is not adsorbed on the resin in 1 0 s hydrochloric acid ( 2 ) . Phosphate rock containing in excess of 100 mg. of calcium phosphate per sample caused losses due to coprecipitation of uranium with calcium sulfate in the solution step. These losses n cre minimized by using the double colunin separation. I n 1 0 s hydrochloric acid, neither calcium nor phosphate was adsorbed on the resin. As uranium and iron were adsorbed, the effect of high concentrations of iron was studied. Iron concentrations in excess of 200 nig. per sample caused uranium leakage in a resin volume of 5 ml. I n such cases the resin volume should be increased. To determine the accuracy of the procedure, a series of uranium standards was analyzed, a majority obtained from the Colorado Plateau (Table 11). The reported uranium content of the New Brunswick and AEC standards is a statistical average from the results of several independent laboratories. The 958
ANALYTICAL CHEMISTRY
Rapid Spectrophotometric Determination of ManganeseTriethanolamine and Peroxide Complexes of Manganese(Ill)Correction procedure by Bruno [Accad. A pugliese xi., Atti e relaz. 11, Pt. 2, 409 (1953)] for the spectrophotometric PRIOR
leucogranite mas supplied by the California Institute of Technology and analyzed in replicate by independent analysts using chemical extractions and ultraviolet fluorescence. The National Lead samples are a series of fluorometric standards from Grand Junction, Colo. CONCLUSIONS
The procedure is adaptable to routine analyses and can be done with a niinimum of expense and equipment, especially in laboratories where ion exchange is in use or a fluorometer ip not available. Interferences from high thorium or calcium phosphate are minimized by double adsorption. Analytical detection may be expected for uranium concentrations as low as O . O O O l ~ O . The average deviation is 0.00270 or better for uranium values between 0.1 and 0.01%. For uranium values between 0.01 and O . O O l ~ o the accuracy of the determination is to approximately &lo%. ACKNOWLEDGMENT
The authors thank John K, Butler and his staff, Mackay School of Pliines, for suggestions and encouragement.
determination of manganese(I1) (sic) in alkaline triethanolamine solution is acknoKledged. This procedure recommended the determination a t 625 mp for solutions containing 5 to 30 y of manganese per ml., but the nature of the reduction and the identity of the colored species were not elucidated. The upper limit of 30 y per ml. for the Bruno method corresponds to our concentration limit of 0.5mM [AXAL. CHEar. 31, 146 (1959)], above which R-e could not effect the rapid quantitative air oxidation of the manganese(I1). For more concentrated solutions, the manganese(II1)-peroxide complex interferes and must be decomposed as described previously. The molar absorbance index of the manganese(II1)triethanolamine complex a t 625 mp is slightly greater than that at 438 mh, but the latter wave length provides a more specific method because copper(11) and iron(I1) do not interfere. I n spite of their simplicity, neither of these procedures can be recommended for concentrations less than about 1mM because the molar absorbance of the manganese(II1)-triethanolamine complex is not sufficiently large to give accurate results; more sensitive procedures are available for dilute solutions.
E. R. NIGHTINGALE, JR.
