Determination of Zirconium in Uranium Fissium Alloys HAROLD B. EVANS, ALICE M. HROBAR, and JAMES H. PATTERSON Argonne National laborafory, lernonf, 111.
b Two methods are presented for the separation o f zirconium from fissium alloy, the fuel to b e used for the Experimental Breeder Reactor II. One method separates zirconium, molybdenum, and palladium from the other components b y precipitation with cupferron. Zirconium i s separated from molybdenum and palladium b y successive precipitation with ammonium hydroxide. The other method, which i s simple and adaptable to routine analysis, consists of ammonium hydroxide precipitations, followed b y precipitation with p-chloromandelic acid. The zirconium i s determined spectrophotometrically as the alizarin sulfonate lake.
I
THE development of methods for the remote pyrometallurgical processing of spent fuel elements from the Experimental Breeder Reactor I1 (EBR11), fission products of atomic numbers 40 through 46 were very difficult to remove. These fission products are calculated to reach an equilibrium concentration after sereral recycles, at which time the rate of formation in the fission process is balanced by the losses due to burnup, decaji, and partial removal in processing. A typical equilibrium mixture is shown in Table I. This alloy has improved radiation stability and metallurgical properties over pure uranium. 'To provide a fuel whose properties do not change with time, the reactor is t o be fueled with an alloy, called fissium, rrhich contains the natural st'able forms of these elements (except technetium) in approximately these concentrations. I n the iiiaiiufacture of t'he fuel elements, analyses for zirconium, as n-ell as the other fissiuin elements, were needed for control of t,he procms. The alizarin sulfonate method ( 2 , 11) for the spectrophotometric determination of zirconium in the presence of uranium is now being used in this laboratory for the analysis of other alloys. A differential spectrophotometric method is suggested for good precision by Manning and K h i t e (10). The 'other fissium elements interfere in the alizarin method and must be separated from the zirconium. Separation would also be necessary for such methods as titrimetric or neutron activation analyses as well as other spectrophotometric analyses using such reagents as chloranilic
x
acid (3, 12). Thus the principal problem is the separation of zirconium from the other elements of this alloy. Many workers have used ion exchange for the study of the solution chemistry and separation of small amounts of the desired constituent. Stevenson, Franke, Borg, and X'errvik (16) suggested a scheme for the separation of the platinum metals using Don ex 50 with 2 to 16% cross !inkage. This system i5 now being investigated to aqcertain where molybdenum, zirconium, and uranium might fit into their procedure. The paper chromatographic method, as suggested by Kember and Kells ('73, with modification of the solvent miuture, also offers possibilities for the separation of zirconium. Under the conditions used in this separation, zirconium has very little migration, and only rhodium would interfere. Solvent extraction methods of separation for zirconium, utilizing mixed phosphoric acids in di-n-butyl ether, acetylacetone, fluorinated compounds, hesone, tributyl phosphate, and thiocyanic acid have been used b y others with moderate to good success. Tri-n-octyl phosphene oxide has been used by K h i t e and Ross ( I S ) for zirconium separations. This solvent may have application to the present system. Many methods and reagents have been suggeeted for the separation of zirconium by precipitation. I n the present work two procedures have proved successful. Cupferron (15) has long been used for the precipitation of zirconium and other metal ions from solution. The applicability of zirconium methods has been greatly enlarged since the introduction of mandelic acid as a reagent by Kumins (9). Oesper and Klingenberg (IS) showed that p-chloro- and p-bromomandelic acids precipitate zirconium more completely without a large excess of reagent. Klingenberg and Papucci (8) dem onstrated the specificity of the halogenated mandelic acids by analyzing zirconium in the presence of titanium alloys. Others who contributed significantly to the application of the mandelic acids to zirconium analysis are Hahn (5, 6 ) , who developed a direct spectrophotometric determination in ammoniacal solution, and Bricker ( I ) , who used these reagents to determine zirconium in plutonium alloys. Quantitative recovery of zirconium I\ 3 3 also accomplished using p-hy-
Table I. Calculated Equilibrium Fission Product Concentration ( 7 4 ) ( 5 wt. yo new metal per cycle)
Weight, %
Element Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium
0.10 0.01 3.42 0.99 2.63 0.47
0.30
droxyphenylarsonic acid as the precipitating reagent. Holyever, this was abandoned in favor of the p-chloromandelic acid method, as arsenic has a marked interference in the alizarin determination step and must be eliminated, with difficulty. as the volatile bromide from a perchloric acid solution. EXPERIMENTAL
Apparatus. Spectrophotometer, Beckman Model DU, equipped with photomultiplier attachment, tungsten light source, and Beckman DU power supply. hlatched set of four, 1-cm. path, Cores absorption cells. Reagents. p - CHLOROUAKDELIC ACID, 2.9y0solution. AEROSOL,1% aqueous solution. ZIRCONYLCHLORIDE SOLUTIOKS. Dissolve 39 grams of zirconyl chloride in about 150 ml. of 4 M hydrochloric acid a n d dilute t o 1 liter iyith 4144 hydrochloric acid in a. tared volumetric flask. Solution contains about 20 ing. of zirconium per ml. Standardize by precipitation of a weighed aliquot with 6% cupferron from a l0g;b sulfuric acid solution. Ignite and wveigh as ZrOs. Prepare more dilute solutions from this standard by using weighed aliquots. CUPFERROX, 67, solut,ion. Prepare as needed by dissolving 6 grams of cupferroii in 100 ml. of water. Keep the dry reagent in a cool, dark place, preferahly under a bag of ammonium carbonate wrapped in a fine mesh cloth. WASH SOLCTIOS.Dilute 50 ml. of concentrated hydrochloric acid t o 500 ml. To this solut'ion add 0.75 gram of cupferron. Stir until the cupferron is dissolved. Prepare as needed. URASTL CHLORIDESOLUTION(20 ing. uranium per m1.j. Dissolve 6 grams of uranium trioxide in 5 ml. of concentrated hvdrochloric acid and dilute to 250 nil." S O D I L X hLIZ.lRIlv SULFOKATE, 0.05% VOL. 32, NO. 4, APRIL 1960
481
solution. Dissolve 0.5 gram of this reagent in 500 ml. of water. Filter, wash, and dilute to 1 liter. Dissolution of Sample. Weigh o u t a sample of t h e alloy as turnings containing from 0.15 t o 0.46 mg. of zirconium and transfer t o a 150-ml. beaker. Add 5 ml. of water and 15 ml. of a 5 t o 1 hydrochloric-nitric acid 6OhtiOn. T h e mixed acids should be added slon-ly to the covered beaker t o prevent a n y losses due t o hydrogen evolution. After t h e evolution of gases has ceased, add another 15 ml. of the hydrochloric-nitric acid solution and digest at incipient boiling temperature for 0 . 5 hour. Cool, add 5 ml. of concentrated sulfuric acid and 3 nil. of concentrated perchloric acid, and evaporate to strong fumes of perchloric acid. Cool, carefully rinse down the cover and sides of the container, and again fume strongly. (This fuming step is very critical when the p-chloromandelic acid method is to be used, as small amounts of fluoride and ruthenium interfere. The authors have found no such interference in the cupferron method.) Some of the experimental fissium alloys have contained up to 25% fissium metals and are not dissolved completely by the procedure recommended. Alloys that contain more than 15% of the fissium elements are dissolved in platinum containers with concentrated nitric acid that is 0.2M in hydrofluoric acid. The hydrofluoric acid must be removed by thorough fuming with sulfuric acid before the solution is transferred t o glass. Silicate and aluminum ions that may be formed by dissolution in glassware interfere with the spectrophotometric method as does any residual fluoride. Repeated strong fuming with sulfuric acid is necessary for complete removal of hydrofluoric acid. Fuming with perchloric instead of sulfuric acid gives low results, probably because of incoiiidete removal of fluoride. Procedure A. Transfer t h e dissolved alloy t o a 400-ml. beaker. Add 25 ml: of concentrated sulfuric acid and 250 ml. of water. Cool t h e solution t o about 10" C. and slowly add, while stirring, 10 ml. of freshly prepared 6% cupferron solution. Filter with gentle suction through a platinum filter cone, using R h a t m a n S o . 42 filter paper, into a flask containing 2 ml. of 6% cupferron solution to test for complete precipitation. Wash the precipitate 11-ith a cold 1.2M hydrochloric acid solution containing 1.5 grams of cupferron per liter. Fold the precipitate into the filter paper and transfer i t to a 150-ml. beaker. Add 30 ml. of a 1 to 6 hydrochloric-nitric acid solution and digest on the hot plate until the organic matter has been thoroughly decomposed. Add 6 ml. of 3 to 2 perchloric-sulfuric acid solution and evaporate to fumes of sulfur trioxide. Cool and wash the cover and sides of container and again evaporate to fuming. The solution should be clear at this point. Allow t o cool. Transfer the sulfuric acid solution to 482
ANALYTICAL CHEMtSTRY
sulfonate solution. Dilute to volume and mix. After 50 minutes, measure the absorbance against a reagent blank (consisting of 10 ml. of 1.2M hydrochloiic acid and 5 ml. of 0 05% sodium alizarin sulfonate solution) a t 520 mk using the blue photocell n i t h a slit of 0 02 mm. and a sensitivity setting of 3. Determine the zirconium concentration by using the C / d (concentration/absorbance) ratio obtained from measurement of synthetic standard fissium solutions. This ratio is the reciprocal of the slope of the usual Beer's law curve.
6
A
SAISPLE PREPARATION
1
PRECIPITATlOh.
Figure 1 , Schematic diagram for zirconium analysis in uranium fissium alloys 0.4 (
1
l
- = o4 5 0
o
z
_ - - - - - _-_- - _ _ _ 475
500
WIVE
525
LEYGTH.
550
575
600
650
mtll#mlcronl
Figure 2. Absorption spectra of zirconium-Alizarin Red S complex Spectracord 4000 1-cm. cells, Zr = 3.17 X 1 O-bM Scanning time = 3 minutes Reagent blank 1M HCI 0.12M HCI 1M HCI shifts p e a k to ultraviolet, 487 mp
---
0.190
I
I 0
,
2 T,ME
3
ihO",l,
Figure 3. Development time for zirconium-Alizarin Red S complex M o d e l DU Beckman with photomultiplier attachment. Slit 0.01 mm. 5 2 0 mp. Sensitivity = 3. 1 -cm. cells 2 . 8 2 p.p.m. zirconium
a centrifuge tube using a minimum of 1 . 2 N hydrochloric acid. Add 20 mg. of uranium as a carrier and dilute to 20 ml. with water. Add concentrated ammonium hydroxide dropJTise until a permanent precipitate is observed, then add about 1 ml. in excess. Cool in an ice bath and centrifuge. ilspirate off the supernatant liquid using care not t o disturb the precipitate. Add 1.0 to 1.5 ml. of concentrated hydrochloric acid dropwise, iTashing down the sides of the tube. Heat in a hot tyater bath until the precipitate is dissolved. then dilute to 20 ml. Repeat the ammonium hydroxide precipitation twice more. After the third precipitation. add 10 ml. of 1.236 hydrochloric acid to the precipitate and place the tube in a boiling water bath until the precipitate is dissolved. Transfer the solution to a 100-ml. volumetric flask and dilute to about 80 ml. with water. Mix well and add 5 ml. of 0.05yo sodium alizarin
RESULTS. Fourteen synthetic fissium solutions mith known zirconium contents ranging from 0.2 to 0.4 mg. were carried through the procedure with a standard deviation per determination of 0.62%. DISCUSSION.Figure 1, A, is a schematic diagram illustrating the various steps in the analysis of zirconium using cupferron. The zirconium, along with palladium and molybdenum, is precipitated with the cupferron. These cations that are precipitated with the zirconium undoubtedly also serve as carriers and aid in obtaining quantitative recovery. The series of ammonium hydroxide precipitations using uranium as a carrier accomplishes the separation of zirconium and uranium from molybdenum and palladium, which remain in solution as the molybdate and the palladium ammine complex, respectively. The effectiveness of other cationic carriers was not tested. Three ammonium hydroxide precipitations are necessary to eliminate completely the interference from ions that would form colored complexes with the alizarin sulfonate or prevent formation of the zirconium lake. I n the formation of the alizarin sulfonate complex ~ i t zirconium h the acidity is controlled by using a known volume of a 1.2M hydrochloric acid solution. Slight variations in p H do not affect the spectrum, but a greatly increased acidity causes a lowered absorbance and a shift of the maximum toward the ultraviolet, as shown in Figure 2. I n a series of determinations where 20 ml. of 1.2M hydrochloric acid was used instead of 10 ml., the absorbance was consistently 2 to 3Yc low. The maximum absorbance under the specified conditions is a t 520 mp. The interference of uranium in concentrations up to 1 gram per 100 ml. n a s negligible at this T-iave length. The molar absorbance index is 6375. Thus, about 3 y per ml. nil1 develop a n absorbance slightly greater than 0.20 in 1-em. cells. Figure 3 is a graph of the development time of the zirconium-alizarin lake. There is a 50-minute period of stability during which the absorbance can be measured. A break was observed in the linearity of the standard curve a t a mole ratio
b
(alizarin to zirconium) of 1.5, and the calculated maximum zirconium that can be used a t this reagent concentration is 477 y per 100 ml. This ratio probably indicates that the Alizarin Red S used was impure, as extensive work by others ( 2 , 11) has shown a mole ratio of 1 to 1 between zirconium and alizarin. Beer's lam is obeyed for concentrations of zirconium greater than 477 y when the reagent concentration is increased. The working range giving the best results was found to be 150 to 4% y per 100 ml.
Procedure B. Dissoli-e a weighed sample of t h e alloy containing 0.15 to 0.45 mg. of zirconium by t h e procedure previously described. Fume strongly t o remove t h e last traces of ruthrnium. Continue fuming t o near dryness. Add 2 ml. of concentrated hydrochloric acid a n d rinse t h e sides of t h e container x i t h a minimum a m o u n t of water. Cover and digest a t incipient boiling tempcrature for 2 minutes. Cool and transfer to a 40-1111. gracluated centrifuge tube and dilute to 15 mi. Add concentratsed ammonium hydroxide slowly with swirling until a slight precipitate persists. Dilute to 30 ml. and add a n ~ m o n i u nhydroxide ~ until the solution is a,lkaline. Mix and cool in an ice bath. Centrifuge a t maximum speed for 5 minutes. Aspirate off t'he supernatant liquid, taking care not to disturb the precipitate. ,4dd 2 nil. of concent'rat'ed hydrochloric acid and heat on a water bath until the precipitate dissolves. Dilube to 15 nil. and again prt.cipitat,e with ammonium hydroxide. Centrifuge and remove the supernatant' liquid by aspiration. Add 2 drops of hyclrochloric acid per 100 mg. of uranium plus 2 ml. in excess. Dilute to 10 ml. and bring to incipient boiling temperature. Add 5 ml. of 2.9% p-chloromandelic acid while sn-irling. Digest on a steam bath for 45 minut'es. Cool in an ice bath and add about 20 drops of 1:5$ Aerosol O T to the sides of the cont'ainer while swirling. Centrifuge for 5 minutes. Remove the supernatant liquid by aspiration. To the precipitate add 8 drops of nitric acid, 25 drops of sulfuric acid, and 15 drops of perchloric acid, allowing the acids bo wash the sides of the tube during addition. Clamp the tube in a Cenco hot cone heater. Adjust the 1-ariac for maximum voltage (115 volts). When the scilut'ion begins to fume, reduce the setting to 80 volts. Fume until the solution becomes quiescent, and then for 15 minutes longer. Rrmove from the heater and allorv to coo!. Add 20 mg. of uranium as uranyl chloride anti dilute to 20 nil. Precipitate the zirconium and uranium wit'h ammonium hydroxide. Cool in a n ice bat,h and centrifuge for 5 minutes. Reniove the supernatant by aspiration. Aftrr adding 10 ml. of 1.251 hydrochloric acid. hrat to incipient boiling. K h e n the precipitate is completely dissolved. transfer to a 100-nil. volumetric flask. Dilute to about 80 ml. with water and add 5 ml. of 0.05%
sodium alizarin sulfonate solution. Dilute to volume. After 1 hour, measure the absorbance against a reagent blank at 520 mp using the blue photocell with a slit width of 0.02 mm. and a sensitivity setting of 3. RESULTS. Twenty-two zirconium determinations 15-ere made using synthetic solutions of the fissium elements (Table 11). The standard deviation for a single determination was 0.8770. The results indicate that alloys as low as 0.017, in zirconium can be analyzed accurately by this method. DISCU~SION. The optimum conditions for the zirconium p-chloroniandelate precipitation with respect to reagent concentration, effect of pH, temperature, digestion time, etc., will not be discussed here inasmuch as the subject is adequately covered elsewhere. This method of Separation, which is schematically represented in Figure 1, B , has the folloTl-ingadvantages over the cupferron method: elimination of the time-consuming filtration and wet-ashing steps; easy adaptation t o routine analysis; simplicity, in that most of the operations are carried out in the same container; and greatcr specificity of the precipitating agent. Ruthenium is removed as the volatile tetroside by fuming with perchloric acid in the sample preparation procedure. Molybdenum and palladium, as well as sulfate ion, are left in the supernatant liquid in the precipitations with ammonium hydroxide. Thus, the only need for either p-chloromandelic acid or cupferron precipitation is the separation from rhodium, as the concentration of niobium in this alloy is too small to interfere and interference from uranium is negligible. If potassium hydroxide is substituted for ammonium hydroxide, the rhodium also is soluble, but the recovery of the zirconium was not alm-ays quantitative. Interferences in the SpectrophotoSiobium, metric Determination. molybdenum, antimony, ruthenium, palladium, tungsten, ferric ion, aluminum, thorium, rhodium, titanium, and organic hydroxy acids interfere with the spectrophotometric method for zirconium (4, 11, 17). Ruthenium is the worst offender, causing a n error in the zirconium equiralent to 10% of the weight of the ruthenium. The zirconium equivalence of molybdenum, rhodium, and palladium is about 1%. The anionic interferences are silicate, fluoride, sulfate, nitrate, and phosphate. The addition of phosphate must be avoided, as it would precipitate zirconium. Fluoride and nitrate are removed by fuming. Sulfate ion decreases the absorption if its mole ratio to zirconium is greater than 50. However, sulfate is removed by the various precipitations that are used in the separation. Organic compounds are de-
Table ll. Analysis of Synthetic Solutions of Fissium Elements Using Procedure B
Uranium, Mg.5 10 10 20
20 200
400 400 400 500 600 800 800 800 1000 1000 1000 1000
Zirconium, Mg. Taken Found 0.319 0.318 0.315 0.315 0.382 0.386 0.298 0,300 0.334 .~~ 0.336 0.19i 0.193 0.152 0.153 0.463 0.462 0.124 0.128 0.427 0.428 0.251 0,253 0.323 0.324 0 347
0 309 0 301 0 324 0 302 0.299 0.280 0 269 0 278
0 'G
Error -0.3 0.0 -1.0 +O. 7 +0.6
0.0
+n ,
7
-0.2
+3.2
-0.2
-0.8
-0.3
0 34.5
-0 A
0 0 0 0
+O 7 0 0 -1 0
309 303 324 299 0.297 0 28.5
0 0
-0.7 i.1.8
0 265 -1 5 0 281 4-1 1 0 323 0 321 -0 6 a Other elements present: molybdenum, 16 mg.; ruthenium, 4.5 mg.; rhodium, 11 mg.; palladium, 10 mg.
stroyed in the wet ashing. The zirconium is separated from the cationic interferences by Procedure A or B. LITERATURE CITED
(1) Bricker, C. E., JTaterbury, G. R., ANAL.CHEX.29, 558 (1957). (2) Flagg, J. F., Liebhafsky, H. A., Winslow, E. H., J . Am. Chem. SOC. 71, 3630 (1949). (3) Frost-Jones, R . E. U., Yardley, J. T., Analyst 77, 468 (1952). (4) Guenther, R., Gale, R. H., Knolls Atomic Pori-er Laboratory, Schenectady, N. Y., KAPL-305 (1950). (5) Hahn, R. B., ANAL.CHEM.2 1 , 1579 (1949). (6) Hahn, R. B., Weber, L., Ibid., 28, 414 (1956). (~, 7 ) Kember. K.F.. TT?ells. R. A., Analust 80, 735 (1955). ' (8) Klingenberg, J. J., Papucci, R. h., ANAL. CHEM.30, 1063 (1958). (9) Kumins, C. ii., Ibid., 19,376 (1947). (10) Manning, D. C., White, J. C., Ibzd., 27, 1389 (1955). (11) Mayer, A., Bradshaw, G., Analyst 77, 476 (1952). (12) Menis, O., Oak Ridge National Laboratory, Rept. KO. ORNL-1626 (1954). (13) Oesper, R. E., Klingenberg, J. J., ANAL.CHEW21, 1509 (1949). (14) Schmidt, J. H., Rodger, W. A.J Levenson, XI., Argonne National Lsboratory, TID-7534, Book 2. (1:) Smith, Frederick G., Chemical co., The Preparation, Properties and Analytical Application of Cupferron and Neo-cupferron," 1938. (16) Stevenson, P. C., Franke, A. A., Borg, R. C. (to U. S. Atomic Energy Commission), U. S. Patent 2,714,555 (August 2, 1955). (17) FT'engert, G. B., AXAL.CHEJI. 24, 1449 (1952). (18) White, J. C., Ross, W. J., Oak Ridge National Laboratory, Rept. NO. ORNL-2498 (1958). RECEIVEDfor review April 30, 1959. Accepted December 17, 1959. Based on work performed under the auspices of the U. S. rltomic Energy Commission. VOL. 32, NO. 4, APRIL 1960
483
