Solubility of Yttrium Oxalate A. M. FEIBUSH,l KEITH ROWLEY, and LOUIS GORDON2 Deparfmenf o f Chemistry, Brookhaven National laboratory, Upfon, I. I., N. Y., and Syracuse University, Syracuse 10, N. Y. ,The solubility product of yttrium oxalate and the dissociation constants of the yttrium oxalate complexes have been measured by the method developed by Crouthamel and Martin. The solubility product was determined The complex ions to be 5.34 X 1 O-*'. 3 X detected were: Y(Cz04)+, KI
lo-';
Y ( C Z O ~ ) ~K- P,
and Y(C20&---,
8 X lo-";
K 3 g 3.4 X 1 O-12.
A
for the estimation of rare earth oxalate solubility products and rare earth oxalate complex dissociation constants has been presented by Crouthamel and Martin (1, 2 ) , who applied the method to ytterbium, cerous, and neodymium oxalates. This paper extends the study t o yttrium oxalate. Although yttrium is not a member of the rare earth group, its chemical similarity to that group indicated that a similar treatment would be satisfactory for the evaluation of the equilibrium constants, METHOD
EXPERIMENTAL
Materials. Yttrium oxide was obtained from t h e Institute for Atomic Research, Ames, Iom-a. It was reported t o be 99.8% Y203,0.2% Dy203, 0.02% TbrO7, and was used without further purification. T h e oxide was ignited to constant weight, and Present address, Texas Research Center, Beacon, N. Y . Present address, Department of Chemistry and Chemical Engineering, Case Institute of Technology, Cleveland 6, Ohio.
A Mylar end window (0.8 mg. per sq. em.) counting tube using a Q gas flush (98.7% helium, 1.3% butane) and a
weighed portions were dissolved in dilute perchloric acid to prepare standard solutions. Radioactive yttrium was used to facilitate analysis. Yttrium-91 was supplied from the Oak Ridge National Laboratory in carrier free form as Yg1Cl3in hydrochloric acid solution, and has a radiochemical purity of greater than 99.0%. This isotope has a 57.5-day half life, and emits b- rays of two energies, more than 99% of which are 1.55 m.e.v. (4). An extremely weak y ray is also reported. Yttrium chloride mas converted to the perchlorate by adding dilute perchloric acid and evaporating to dryness. The residue was dissolved in water and used with the stable 1%trium perchlorate solution to prepare yttrium solutions, and solid yttrium oxalate of known specific activity. The initial specific activity was 7.8 x lo7 counts per minute per mg. of yttrium. Procedure. Equilibrium was approached in oxalate buffer solutions by precipitation of yttrium oxalate, and b y equilibration with preformed yttrium oxalate. T h e solutions were shaken in a thermostat a t 25.0' 0.2" C. Analyses were made after 3 days and remained constant thereafter. Some of the solutions mere retained for a month or longer nith no change observed in the variables. The pH was measured with a Beckman Model G pH meter and the total oxalate was determined by titration with pernianganate. The yttrium content was measured by radioassay using the liquid mounting technique described by Freedman and Hume ( 3 ) . Because there was no need to preserve the samples, they were not plastic coated before counting
suitable scaler were used for the 0ray intensity measurements. Threemilliliter aliquots of the solution were pipetted into 5-ml. beakers which mere positioned reproducibly under the counting tube in a n aluminuni block. Each solution was analyzed for the three components a t least three times and an average of the results was used in the subsequent calculations. The necessary activity coefficients and oxalate ion activities Ivere calculated in the manner outlined b y Crouthamel and ivartin. DISCUSSION
OF
RESULTS
The experimental results are given in Table I, and a plot of the negative logarithm of the observed total yttrium concentration us. the negative logarithm of the oxalate ion activity is shown in Figure 1. Except for the region where -log(Ca04--) is betneen 6.5 and 4.5, the curve is of the same general type as that obtained for cerium (3). The slope of the right-hand portion is very close to 3/2, indicating the formation of a trioxalate complex. The slope on the left-hand portion is also very close to - $ I 2 , indicating that in this region none of the yttrium oxalate complexes are present in significant amounts. Between the point of minimum solubility and the straight-line portion of slope - 3 '2 on the left, the points do not seem to lie on a smooth curve. I n this region more yttrium is found in the solution than if the solubility curve Tyere smooth. There is also considerably more scatter in this region. Measure-
*
I
1
0
I I I I -6.0 -5.0 -4.0 -3.0 LOGARITHM OF OXALATE ACTIVITY
I
-2 0
- 1.0
Figure 1. Plot of logarithm of observed yttrium concentration vs. logarithm of oxalate ion activity X Yttrium oxalate precipitated
0 1610
Preformed yttrium oxalate a d d e d
ANALYTICAL CHEMISTRY
-60
1 -50 LOGARITHM
1 30 -40 OF OXALATE ACTIVITY
I
-20
-\ 0
Figure 2. Plot of logarithm of calculated yttrium concentration vs. logarithm of oxalate ion activity
ments from experiments attempting to approach equilibrium from both directions are included in this region of the curve, and there is no striking difference between the results. i l n attempt was made to correlate the results in the central portion of the curve with the binoxalate ion activity, pH, and formation of other complex species in the solution. No systematic relationships could be found. The results in this region h a r e not been explained. It is possible that colloidal suspensions are stable in this region, resulting in a lack of true equilibrium. Another possible source of error may be the counting data. I n this region of minimum solubility, the counting rate was very lorn. Therefore, it was necessary to count for relatively long periods of time, during which some evaporation of the liquid counting sample may have occurred. Such evaporation n-ould tend to increase the counting rate, but would be unlikely to result in the reproducible measurements which were obtained. The equilibrium constants for the system were evaluated using the data from those parts of the curve which best fitted the theoretical prediction. The data used are indicated b y asterisks in Table I. The total yttrium concentration in solution can be represented b y the equation
where
Table I. NO.
Pa
PH
1* 2* 3* 4* 5* 6* 7% 8* 9* 10
0.412 0.263 0.253 0.266 0.0103 0.267 0.143 0.266 0.450 0,148 0.00103 0.136 0.0579 0.0733 0.0142 0.0260 0.173 0.00513 0,00886 0.0686 0.187 0.0194 0.121 0.101 0.0739 0.119 0 0379 0.0744 0.0744 0.0875 0.00784 0.0828 0.0470 0.0428 0.0531 0.0439 0.0564 0,00443 0.00625 0.0121 0.0655 0.0588 0.0656 0.0662 0.00503 0.0542 0.00473 0,0487 0,023ti 0,0317 0,0871 0.157 0,0683 0,0746 0.106 0.628 0.121 0.0397 0.0419 0.114 0.162 0.0887 0,199 0,0965 0.136 0.250 0.147 0.300 0.358 0.354 0.367 0.595 0.493
0.52 0.71 0.72 0.70 2.02 0.70 1.00 0.71 0.49 0.93 3.01 0.98 1.34 1.19 1.90 1.67 0.82 2.65 2.09 1.86 1.47 1.76 0.98 1.09 1.19
11
12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 * 51* 52 * 53 * 54 *
55 *
where parentheses (or brackets) refer to activities. The constants evaluated b y the method of averages (5) are K** = 5.34
x
10-28
h-1Z 3 X 10-7 KPG 8 X 10-11
K3 = 3.4 X 10-12
The calculated' yttrium concentrations based on these constants are listed in the last column of Table I. The precision index ~'2% where di is (log [ Y l t o t a l . calcd. - log [Yltotal. obad..) and N is the number of points, was 0.119 for the points used in the calculation. A plot of the logarithm of the calculated values of the total yttrium con-
Data from Solubility Experiments
56 * 57* 58 * 59 * 60 * 61* 62 * 63 * 64 * 65 * 66* 67 * 68 * 69 * 70 * 71* 72 73
1.oo
1.48 1.20 1.20 1.14 2.56 1.21 1.53 1.52 1.49 1.51 1.53 3.52 3.12 2.59 1.73 1.86 1.82 1.82 3.54 2.05 4.15 2.35 2.75 2.74 2.17 1.96 2.34 2.51 2.31 2.97 2.80 3.40 3.49 2.99 3.00 3.82 3.30 4.19 3.99 3.52 4.30 3.73 3.85 3.98 4.23 4.65 4.28
2.110 2.089 2.042 1.884 3,790 1.694 2.029 1.517 1.106 1.842 4.272 1.729 1.971 1.601 2.563 2.217 0.617 2.886 2.197 1.854 1.297 1.714 0.584 0,744 0.892 0,589 1.299 0.884 0.884 0.783 2.509 0.892 1,154 1.241 1.164 1.162 1.426 3.026 2.657 2.106 1,098 1,195 1.113 1.114 2.806 1.231 3.112 1.340 1.691 1.521 1.040 0.767 1.185 1,098 0.968 1.302 0.963 1.541 1.538 0.962 0.891 1.319 0.867 1.392 1.180 0.839 1.235 0.726 0.771 0.818 0.827 0,675 0.676
2.97 3.43 3.54 3.66 3.97 3.84 4.06 4.00 3.97 4.20 4.46 4.27 4.41 4.51 4.64 4.60 4.43 4.75 4.77 4.63 4.54 4.50 4.41 4.48 4.45 4 37 4.57 4.51 4.50 4.48 4.72 4.54 4.90 4.60 4.68 4.83 5.00 4.65 4.60 4.68 5.26 5.29 5.31 5.35 4 56 5.31 4.54 5.29 4.93 5.21 5.40 5.61 5.39 5.27 5.38 5.13 5.07 4.98 4.94 4.94 4.85 4.69 4.55 4.64 4.47 4.27 4.42 3.92 4.02 3.92 3.91 3.45 3.51
6.62 6.35 6.29 6.16 6.09 5.97 5.80 5.78 5 76 5.73 5.61 554 5,22 5.07 5.07 L O 1
4.69 4.56 4.47 4.44 4.40 4.39 4.39 4.3'7 4.36 4.36 4 35 4.34 4.34 4.33 4.29 4.28 4.28 4.22 4.20 4.1i 4.12 3.89 3.88 3.86 3.84 3.78 3.77 3.75 3.65 3.60 3.55 3.39 3.30 3.29 3.29 3.27 3.25 3.13 3.08 2.75 2.59 2.58 2.50 2.49 2.35 2.11 2.09 2.00 1.93 1.91 1.88 1.83 1.74 1.69 1.62 1.47 1.48
2.93 3.40 3.49 3.64 4.31 3.90 4.22 4.18 4.08 4.16 4.72 4.49 4.85 4.92 4.98 5.02 5.13 5.27 5.30 5.25 5.22 5.32 5.25 5.49 5.26 5.35 5.31 5.29 5.29 5.28 5.37 5.30 5.20 5.28 5.35 5.36 5.3t1 5.48 5.49 5.47 5.42 5.42 5.42 5.42 5.42 5.51 5.43 5.42 5.43 5.42 5.41 5.35 5.38 5.38 5.31 5.18 5.00 5.12 5.07 4.95 4.81 4.86 4.51 4.54 4.44 4.26 4.32 4.12 4.01 3.80 3.83 3.51 3.55
Ionic strength.
* Xegative logarithm of botal oxalate concentration,
moles per liter. Negative logarithm of total yttrium concentration, moles per liter. Negative logarithm of calculated activity of oxalate ion. e Negative logarithm of total yttrium concentration calculated from constants (see text). * Data used to calculate value of constants.
VOL. 30, NO. 10, OCTOBER 1958
161 1
centration us. logarithm of the oxalate ion activity is shown in Figure 2. The points define a smooth curve having the shape expected from the theoretical prediction. The formation of the trioxalate complex with yttrium is somewhat surprising because Crouthamel and Martin found no evidence for the corresponding complex with >+,terbium or neodymium. This lack was ascribed to steric factors
because both these ions are smaller than cerous, which did form the trioxalate. Yttrium is smaller than the rare earth ions studied by Crouthamel and Martin ( I , 2) and in oxalate precipitations behaves as if it were smaller than all of the rare earth ions, yet the third complex is formed. LITERATURE CITED
(1) Crouthamel, C. E., Martin, D. S., J. Am. Chem. SOC.72, 1382 (1950).
(2) Zbid., 73, 569 (1951). (3) Freedman, -4. J., Hume, D. S . , Science 112, 461 (1950). (4) Kahn, B., Lvon, W. S., Phws. Rev. 98, 58 (1955).
(51 Korthincr. A. G.. Geffner. J.. “Treatment of -Experimental Data,’’ pp. 72-5, Kiley, Kew York, 1943. ~
RECEIVEDfor revieq- August 14, 1957. Accepted May 28, 1958. Research supported in part by the U s. Atomic Energy Commission.
Determination of Boron in Aluminum-Uranium Fuel Elements Application of the Carminic Acid Spectrophotometric Method KENNETH W. PUPHAL, JAMES A. MERRILL, GLENN L. BOOMAN, and JAMES E. REIN Atomic Energy Division, Phillips Petroleum Co., lduho Falls, lduho
b A rapid spectrophotometric method is described for the determination of boron in aluminum-uranium alloys, particularly in nonirradiated reactor fuel element samples. After dissolution of the sample in hydrochloric acid and hydrogen peroxide, the boron is determined without separation, by the carminic acid method. The complexes that uranium and aluminum form with carminic acid have weak absorbances a t the working wave length of 585 mp. Compensation is easily made by including uranium and aluminum in the blank. Under routine conditions, the precision is about 2% standard deviation for reactor fuel containing 0.1 weight boron. A sodium carbonate fusion pretreatment is described for boron analysis in an alloy of aluminum and boron carbide and in boronimpregnated polyethylene tape.
yo
I
fuel technology, the use of burnable poisons such as boron is gaining popularity. The range of reactivity over the life of the fuel is decreased and a more uniform flux distribution is obtained. The fuel of the Engineering Test Reactor (ETR), located a t the Kational Reactor Testing Station in Idaho, contains 83.6y0 aluminum metal and 16.4% uranium metal by weight, with about 1mg. of elemental boron per gram (4). The aluminum is grade 25 and the uranium is highly enriched (>goy0) in the 235 isotope. An alloy of aluminum and uranium metals and boron carbide, prepared by poq-der metallurgy techniciue, is being considered for the future. Satisfactory power output and neutron flux distribuN REACTOR
1612
ANALYTICAL CHEMISTRY
tion of the reactor requires control of both total boron content and boron distribution in the fuel. This requires that many samples be analyzed. Samples of polyethylene tape impregnated with boron are also submitted for boron analysis. This material is used experimentally t o measure reactivity of various fuel element arrays. This work was undertaken to find a rapid and precise method applicable to the three types of samples. One of the specifications for ETR fuel is a limit on the composition of the alloy. The allowable variation in uranium content is on the order of 2 relative %. This corresponds to absolute limits of 0.3 weight % in both the aluminum and uranium. With the ratio of both aluminum and uranium thus restricted, and the need for a rapid method, the choice was made to find a n existing method which could be adapted without preseparations. Spectrophotometric and emission spectrographic methods appeared most promising, The common volumetric method involving titration of a n invert sugar-boric acid complex with standard alkali does not tolerate aluminum and uranium. Spectrophotometric methods based on the chromogenic agents dianthramide ( 5 ) , diaminoanthrarufin (S), and carminic acid according to Hatcher and Wilcox ( 7 ) , were selected because aluminum and uranium were expected not to interfere. The latter method proved most applicable. Direct spark excitation of sample surfaces was not successful because boron n a s found to be segregated in many of the samples. Spark excitation of solutions after acid dissolution m s less pre-
cise and no faster than the spectrophotometric method finally adopted. APPARATUS
A Beckman Model B spectrophotometer was used with matched or calibrated I-cm. Corex cells. Low-boron, Corning 7280 glassware or quartzware was used for sample dissolutions. Dissolutions %-ere made under reflux to prevent loss of boron. Fusions were made in platinum crucibles with covers. Dissolved samples were stored in polyethylene bottles until analyzed. REAGENTS
Reagent grade chemicals were used unless otherwise stated. Distilled water, boron-free, was used throughout. An aluminum-uranium matrix, with the same aluminum and uranium concentration as dissolved and diluted E T R fuel samples, was prepared by dissolving 22.1 grams of a n 81.5% 2 s aluminum-18.5% uranium alloy (the individual metals can be used), and 2.9 grams of 2s aluminum in 600 ml. of 5 N hydrochloric acid. dfter dissolution was essentially complete, 50 ml. of 30% hydrogen peroxide was added. The excess hydrogen peroxide was removed by boiling, and after cooling, the solution was diluted with water to 1 liter. A standard 0.100 mg. per ml. boron solution n-as made by dissolving 0.5716 gram of orthoboric acid (H3B03). in distilled water and diluting to 1 liter ( 7 ) . Boron oxide, prepared by fusing boric acid, also can be used. The 0.05% (w./w.) carminic acid reagent was prepared by dissolving 0.920 gram of carminic acid in 1 liter
