interfacial adsorption in their travel down the column. Hydrocarbon retention on water must then be due in part to adsorption at the gas-liquid interface, and consequently, should be dependent on the surface area/liquid volume ratio for the solvent. (The high liquid loading used in this study was chosen to minimize the surface area/liquid volume ratio.) Other nonidealities which may arise in the hydrocarbon elution from water are gas phase imperfections (9) and solute deviations from Raoult’s Law (excess partial molar free energy of
(9) A. J. B. Cruickshank, M. L. Windsor, C. L. Young, Proc. Royal SOC.(London),A295,259 and 271 (1966).
solution) (10-12). Consequently, unless these nonideality effects can be experimentally isolated from each other or independently computed, thermodynamic interpretation of y may be difficult; however, the large values of the coefficients can be highly useful in the rapid elution of hydrocarbons at temperatures 200’-300°C below their boiling points, RECEIVED for review June 21, 1967. Accepted September 18, 1967. (10) D. E. Martire in “Gas Chromatography 1966,” A. B. Littlewood, Ed., Institute of Petroleum, London, 1967. (11) D. H. Everett and F. L. Swinton. Truns. Furuduy SOC.,59, 2476 (1963). (12) S . H. Langer and J. H. Purnell, J . Phys. Chem., 67, 263 (1963).
Amperometric Determination of Sulfur in Plutonium Sulfide and Plutonium-Uranium Sulfide Ceramic Fuels Harold B. Evans and Shiro Mori Chemistry Diuision, Argonne National Laboratory, Argonne, Ill.
A METHOD FOR THE ANALYSIS of sulfur in plutonium sulfide, and uranium-plutonium sulfide mixture was developed for the program that evaluated the ceramic fuels used in nuclear reactors (I). In the presence of alpha activity, a glove box procedure was adopted that consisted of sample dissolution in a nitric acid-bromine mixture and the subsequent separation of the actinides with Dowex 50 X8 cation resin. The eluate containing the sulfate was amperometrically titrated with lead nitrate solution (2). EXPERIMENTAL
Titrations at the dropping mercury electrode were performed in a Meites-type cell (E. H. Sargent). The DME was adjusted to give a drop rate of approximately 8 per second using a constant mercury reservoir height of 30 inches. Lead nitrate was added to the cell from a 5 X 0.01-ml Koch-type microburet. Helium was used for deaeration and stirring. A 7-mm glass column was filled with 4 inches of Dowex 50 X 8 (100-200 mesh) cation resin (3). The column was conditioned by gravity flow with 20 ml of 3.5M HNOI followed by 60 ml of H 2 0 prior to its use (4). All solutions were prepared from analytical grade reagents. The sodium hydroxide solutions were made from Acculate standard volume solution (Anachemia Chemicals, Ltd.) because the Mallinckrodt analytical grade contained enough sulfate impurities to give erroneous results. Procedure. Three-tenths to 0.5 gram of the sulfide sample was weighed out into a 500-ml round-bottomed flask provided with a glass stopper. Five milliliters of saturated bromine water were added and the flask was placed in a dry ice-
Metallurgy Division-Annual Report, Argonne National Laboratory, ANL-6868 (1963). (2) I. M. Kolthoff and Y.D. Pan, J . Am. Chem. SOC.,62, 3332 (1)
(1940). (3) H. B. Evans, C. A. A. Bloomquist, and J. P. Hughes, ANAL. CHEM.,34, 1692 (1962). (4) I. Prevat, J. Corpel, and P. Regnaud, Proc. Second United Nations Int. Conf. Peaceful Uses At. Energy, 17, paper 1171 ( 1958).
60439
acetone bath. When the liquid was frozen, 5 ml of brominesaturated concentrated H N 0 3 were added and the flask was stoppered immediately (5). When the reaction ceased, the flask was heated briefly to ensure all sulfides had been converted to sulfates. The stopper was removed and flask was heated to drive off the excess bromine. Sample was made up to a volume of 25 ml with 3M H N 0 3 . To an aliquot contaking 1.0-3.5 mg of sulfur, H N 0 3 and H 2 0 was added to make 20 ml of 0.5MHN03 solution; 0.5 ml of M1 NaOH was added, and the solution was transferred to the prepared resin column. The resin column was washed with HpO into a 50ml beaker until approximately 40 ml of eluate were collected. The beaker was covered and cautiously evaporated to dryness. One hour before titrating, the residue was dissolved in 5 ml of H20. The sample was treated as being alpha-contaminated because small amounts of plutonium and americium were still present. The room-temperature sample was transferred into the Meites cell with saturated PbS04 solution. Five drops of 0.04 bromothymol blue indicator and 15 ml of 95 ethanol were added. The final volume was adjusted to 50 ml using saturated PbS04 solution. The pH was about 3.0 and was adjusted to read between 4.0 and 5.0 using 0.005M NaOH. The solution was deaerated for 10 minutes while adjusting the solution temperature to 23 O C. Titration was made at - 1.O V us. SCE with 0.02M Pb(N03)2. The titrant was 3dded in increments of 1 ml prior to the end point and in 0.25-ml increments subsequent to the end point. The app.-oach to the end point was followed by observing the gradual increase in background current. After each addition, the solution was deaerated for 2 minutes before making the current readings. Readings near the vicinity of the end point should be avoided because of the deviation arising from the solubility of PbS04. RESULTS AND DISCUSSION
Both Dowex 1 X4 anion exchange resin and an extraction method using tri-n-octylphosphine (6) for the separation of uranium and plutonium resulted in sulfur losses of 1%. ( 5 ) K. E. Kress, ANAL.CHEM., 27, 1618 (1955). (6) J. C. White and W. J . Ross, Nut. Acud. Sci.-Nut. Res. Council Rept. NAS-NS-3102. VOL 40, NO. 1, JANUARY 1968
217
The precision of the extraction method was about 0.1% using 3.2 mg of sulfur. With Dowex 50W X8, approximately 0.26% of the uranium and 0.36% of the plutonium broke through the column. This was probably caused by sulfate interference. The recovery with this cation resin was approximately 99.7%. The amount of uranium which broke
Table I. Effect of Supporting Electrolyte on Amperometric Titration of Sulfate Av. S
Supporting electrolyte None NaN03 NaN03 NaN03 NHiNOs NHdNO3 NaC104 NHZOH. HCl Ascorbic acid a
No. of Concn., samples" M 5 5 5 5 1 1 2 2 2
recovery, Rel. std. Z dev., Z 100.79 99.14 99.87 99.12 98.0 96.7 80.9 98.4 97.6
0 0.005 0.01 0.02 0.004 0.014 0.10 0.02 0.02
11.29 +1.00 10.25 f0.54
-3.206 mg of sulfur per sample.
Table 11. Amperometric Titration of Synthetic PUS and US-PUS Samples for Sulfur Av. S
s (mg.1 0.9618 0.9618 1.603 1.603 3.206 3.206 6.412 6.412
Pu (mg.) 15 41 15 41 10-23 26-46 15 41
U
(mg.1 15 0 15 0 13-17 0 15 0
S (wt.
Z)
E 5.1 3.8 7.4-12 6.5-12 17.6 13.5
No. of recovery, Rel. std. samples Z dev., Z 99.73
j:
99.70 7 8
99.87 99.69 100.66
):
f0.20 f0.48
Table 111. Analysis of Plutonium and Uranium Sulfides Alloy composition %S Av. % S PUS
1
11.99 12.02 11.93 12.24)
12.20
60% U W O Z PUS 12.19 12.06 12.08}
us
218
0
ANALYTICAL CHEMISTRY
11.98
12.07
through the column was enough to give a high background current at the titration potential of - 1.2 V recommended by Kolthoff and Pan (2). This can be reduced to one tenth the amount by operating at - 1.0 V. Using standard solutions of HzS04, variables in the titrating environment were checked. The optimum pH was found at 5.0 where the sulfur recovery averaged 99.9% with a relative standard deviation of fO.25z. When the pH was reduced to less than 3.0, the sulfur recovery dropped to about 99% while an increase in pH above 5.4 resulted in a sulfur recovery of about 101 %. Tests showed that the type and the amount of supporting electrolyte greatly influenced the final results (Table I). Best results were obtained using 0.01M NaN03. In the absence of an electrolyte, considerable scattering of points on the titration curve was observed. Synthetic samples containing Pu or Pu-U mixtures with varying amounts of standard sulfate as HzS04were made up and analyzed for sulfur (Table 11). The recovery of sulfur from these samples which varied from 1 .O to 6.4 mg of sulfur was between 99.7 and 100.6%. In the recommended range of 1.O to 3.2 mg of sulfur, the total amount of matrix materials that breaks through can be tolerated. Sufficient tests to warrant statistical analysis were made for samples containing 3.2 mg of sulfur only, because this sample composition is approximately stoichiometric. Doubling the sulfur content showed over 100% sulfur recovery. Recovery data for metallurgical samples are shown in Table 111. All of the samples analyzed contained slightly greater than stoichiometric amounts of sulfur although these specimens were initially prepared as US and PUS. The high sulfur content in uranium may be due to the presence of higher sulfides such as US2, USa, uZs3 and U& (7) or defects in the lattice structure. Previous investigators found that the SjU ratio of a monosulfide varied from 0.96 to 1.01 (8, 9). Unfortunately, the variations due to interstitial deposition or lattice defects are too small to detect by chemical analysis. The sulfides of Pu have been studied less extensively, but Pu2S3is known (10).
RECEIVED for review May 19, 1967. Accepted October 9, 1967. Based on work performed under the auspices of the U. S. Atomic Energy Commission.
(7) P. Flaubert, Bull. Soc. Chim. France., 1958,772. (8) P. P. Shalek, Argonne National Laboratory Rept. ANL-6330 (1960). (9) E. D. Cater, Argonne National Laboratory Rept. ANL-6140 ( 1960). (10) R.M.Dell and M. Allbitt, UKAEA, A.E.R.E. R-4253.
