Controlled potential coulometric determination of uranium and neptunium in uranium-neptunium alloys

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Calcium and akin in river water and undated water have been determined by this method, and the results compared with the ordinary method in which the indicators were Patton and Reeder’s for calcium, and E&chrome Black T for magnesium (Table V). This method was more convenient and faster than the ordinary cheiatometric method for calcium and magnesium in water. Departmerr~ofChemistry Faculty of Science Okayama University Okayama, Japan

K. T&r T. K~BATAKE

Summary-A simple procedure for thesuccessivechelatometric titration of caieium and magnesium in natural waters, with 3’,3”-bis(2-hydroxy3~~xy-n~phth~en~o)p~enolph~e~n as indicator, is de&bed. Z~-~me einfache Vorschrift zur chelometrisohen Titration von Calcium und M~~~iurn in Naiad nacheinander Sie arbeitet mit ~,3~-B~(2-hy~oxy-3~boxywird ~~h~e~n. naphthal~~o)phenolphthale~ ais Indikator. R&m&0n de&t une technique simple pour les titmges chelatometriques successifs du calcium et du magnesium dans les eaux natureiles avec la 3’,3”-bis (2-hydroxy-3carboxynaphtaRneazo) pMnolphtalCine comme indicateur. REFERENCES 1. T. Kobatake, ‘I’.Iwachido and K. Toei, TaZanta, 1967,14,607. 2. I. Patton and W. Reeder, Anal. Chem., 1956,2X$1026.

Controlled potential coulometric determination of uranium and neptunium in uraniumneptunium alloys* Tnx need for an analytical method for the dete~atio~ of uranium and neptunium in the presence of each other arose when our Met~l~~~al Laboratory prepared a ~~~-nePt~i~ alloy. It appeared obvious that these two elements could not be determined by the normal amdytical procedures if the necessary precision and accuracy were to be attained. Controlled potential coulometry, however, seemed to offer the necessary precision, accuracy, and freedom from inte~~n~. It would also eliminate the necessity of a separation of these elements before an analysis could be performed. The controlled potential coulometric determination of uranium has been widely investigated, as can be seen from the numerous papers on the subject. I4 Stroman has reported the successful controlled potential coulometric determination of neptunium. There is, however, no report of these elemtmts being determined in the presence of each other.

EXPERIMENTAL Appara tUs

A Numee Model 6000 controlled potential codometric titrator, described by Jones et ~l.,~~~ and mamrfaetured by Nuclear Materials and Equipment Corporation of Apollo, Perinsylvania, was used for this investigation. The titration cell and assembty have been described_* * Work Performed Under U.S. Atomic Energy Commission Contract AT(29-l)-1106,

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Stock solutions of uranium were prepared from standard sample 95Oa, U,O,, obtained from the U.S. National Bureau of Standards. Neptunium stock solutions were prepared by dissolving neptunium dioxide, 99.74% NpO,, in concentrated nitric acid with heating. All other chemicals were reagent grade. Neptunium procedure A cell with a platinum gauze working electrode was used. A H-ml volume of 05M sulphuric acid suu~ortine electrolvte solution was blaced in this titration cell and deaerated for 3 min with a stream’o? argoo. The s6lution was pre;duced at 066 V us. the saturated calomel electrode (SCE) under an argon blanket until the cell current had decreased to 30 ,uA, and was then preoxidixed at 1.02 V us. SCE until the cell current had again decreased to 30 ,uA. An ali uot, containing from 05 to 5.0 mg of neptunium, was transferred to the titration cell, followed % y 025 ml of 0*05M cerium(IV) sulphate solution and @5 ml of a saturated solution of sulphamic acid. The solution was reduced at 0.66 V vs SCE under a blanket of argon gas until the cell current had d ecreased to 30 /LA. The solution was then oxidized at 1.02 V us. SCE until the cell current had decreased to 30 PA. By using the integrated current consumed during the oxidation, the amount of neptunium titrated was calculated by Faraday’s law for a one-electron oxidation. Uranium procedure A 7-ml volume of mercury was used as the working electrode, and 10 ml of 0*5M sulphuric acid supporting electrolyte were transferred to the titration cell. The solution was deaerated for 3 min with a stream of argon gas. The solution was prereduced at 0.085 V vs. SCE under an argon blanket until the cell current had d ecreased to 50 PA, and was then reduced at -0.325 V vs. SCE until the cell current had again d ecreased to 50 ,uA. The integrated current consumed during the reduction was recorded as the background. An aliquot containing from 1.0 to 60 mg of uranium, wastransferred to the titration cell, followed by 0.25 ml of 0.05M cerium(IV) sulphate solution. The solution was again prereduced at O-085 V us. SCE under a blanket of argon until the cell current had decreased to 50 PA. The solution was then reduced at -0.325 V us. SCE until the cell current had decreased to 50 PA. The uranium content was calculated from the integrated current consumed during the last reduction. A correction for the background current was applied. Calibration The coulometer was calibrated absolutely’ for neptunium titrations and relatively8 for uranium titrations with a 5.014 mg/ml uranium standard solution. Five aliquots were titrated coulometrically, and a relative standard deviation (RSD) of 0.15% was obtained. DISCUSSION Neptunium To be certain that the system was operating properly for the neptunium determination, a 5.344 mg/ml neptunium nitrate solution was titrated. Five titrations were made by the procedure above. The average relative error was +0*07 %, and the RSD was 0.21%. It appeared from a study of the uranium and neptunium potentials that uranium should not interfere with the neptunium determination. Six titrations, by the neptunium procedure described, were then made to determine whether uranium would interfere. Various ratios (1: 1 to 100: 1) of uranium to neptunium were titrated, and the results are shown in Table I. The average relative error TABLE

L-RECOVERY OF NE F'KJNIUMINTHE PRESENCE OF URANIUM

NP* w

U present mg

Present

Found

Relative error y0

4761 4.761 4.761 4.761 47.61 4761

5.344 5.344 0.534 0.534 0.534 0.534

5.354 5.335 0.532 0.535 0.535 0.537

i-o.19 -0.17 -0.37 +0.19 +0*19 +@56

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was +O*lO& and the RSD was 0.32%. These results indicate that neptunium can be titrated successfully m the presence of uranium and are in good agreement with previously published results.‘ Uranium After the coulometer had been calibrated, a second uranium standard solution was titrated to check the calibration. This second uranium standard solution had a value of 4.763 mglml. Five titrations were made by the uranium procedure described. The average relative error was -O.OZ%, and the RSD was 0.22%. A study of the uranium and neptunium potentials indicated that if any neptunium(IV) or neptunium(VI) were present during the uranium titration, the neptunium would interfere with the uranium determination. The neptunium(W) interference can be eliminated by a prereduction titration. The neptunium(W) interference was eliminated by the addition of cerium(IV) sulphate solution which oxidizes the neptunium to neptunium(VI). The interference which would be caused by the neptuni~(VI) and the excess of cerium(IV) is eliminated by the prereduction titration. The neptunium solution used in this investigation was titrated according to the procedure of Stromatt’ to determine which neptunium oxidation states were present. It was found that the neptunium was 9356% (VI), 4.98 % (V), and 1.46% (IV). Five uranium titrations were made in the presence of neptunium by the procedure above except that no cerium(IV) sulphate solution was added. The average relative error was +@26% (Table II). Five additional uranium titrations were made following the uranium procedure including the addition of the cerium(IV) sulphate. The average relative error for these five titrations was +0*03 y0 (Table III). TABLE II.--ReCOVERY PRESENCE

OF URANIUM

STANDARDS

WITHOUT

THE cERIuM(Iv)

OF NEPTUNIUM PHATE

Present

5.344 5.344 5.344 5.344 5.344

4.763 4.763 4.763 4.763 4.763

TABLE

III.-RECOVSRY

PRESJJNCE OF NEPTUNIUM

THE SUL-

ADDITION

us W

Np present, mg

IN

Relative error %

Found 4.775 4785 4.771 4.777 4.770 Average

OF URANIUM WITH

STANDARDS

THE CERIUM(Iv)

+025 + 0.46 +0.17 +0*29 +0*15 -t-0.26%

IN

THE

SULPHATE

ADDITION

Np present, W 5.344 5.344 5.344 5.344 5.344

I-J, mg Present

Found

4763 4.763 4.763 4.763 4.763

4.760 4.775 4.763 4.760 4.765 Average

Relative error o/0 -0.06 +0.25 &O+Xl - 0.06 +0.04 +0.03 %

It is apparent from these results that cerium(IV) sulphate must be added to the uranium sample to oxidize any neptunium(W) which may be present. This step has been incorporated into the uranium procedure. Interferences There are only a few ions which will significantly interfere with the neptunium

titration.

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Short communications TABLB IV.-Resu~rs TlTFMllON

Np found, %

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OF ~~NTROLLBDPOTENTULcouLoMl3nuc OF

URANIUM-~

Average, %

ALLOYS

U found, %

Average, %

99.3

0.816 0817

0817

zz*: 99.2

992

0.814 0.818

0.816

99.2

0.818 0.820

0.819

0.823 0.825

0.824

z: 991 992 99.1 99.1 99.0 99.1

991 99.1

are gold, platinum, mercury, thallium, and chloride at concentrations of O*lM or greater. Plutonium and palladium will cause only slight interference. The number of ions which would interfere with the uranium titration is greatly reduced by the prereduction step. This step will eliminate the interference from the more electropositive ions, such as iron(III), neptunium(VI), plutonium(IV), and cerium(IV). Ions that are more electronegative than uranium will not cause interference. The ions which will interfere are those which will react bismuth(III), copper(I), at the cathode during the uranium titration, namely antimony(III), and molybdenum(VI). CONCLUSIONS The results have shown that neptunium and uranium can be determined by controlled potential coulometry in the presence of each other. The procedures outlined above have been used to determine the concentrations of uranium and neptunium in uranium-neptunium alloys. The results of these titrations are presented in Table IV. Chemistry-Physics Research and Development The Dow Chemical Company Rocky F&s Division Golden, Colorado, U.S.A.

C. E. PLWK@

Analytical Service Laboratories The Dow Chemical Company Rocky l%zts Division Golden, Colorado, U.S.A.

w. s. PoLKINtxIoRNE

Summary_--A controlled potential coulometric titration method has been developed for the determination of neptunium and uranium in the presence of each other. The recovery of-a neptunium standard in the presence of uranhun was 100*02% with a relative standard deviation of 0.13 %, and the recovery of a uranium standard in the presence of neptunium was 100*03% with a relative standard deviation of 0.13 %. Zusanunenfassung-Eine coulometrische Titrationsmethode bei konstanter Spannung wurde zur Restimmung von Neptunium und Uran nebcneinander entwickelt . Die Au&cute bei einem Neptuniumstandard neben Uran war 100,02 % mit ehrer relativen Standardabweichung von 0,13%, die Ausbeute bei ehrem Uranstandard neben Neptunium 100,03 % mit emer relativen Standardabweichung von 0,13 %. R&stun&-On a tlabore une m&ode de titrage coulom&rique a B potentiel control6 pour le dosage du neptunium et de l’uratdum en presence l’un de l’autre. Le rendement dun dtalon de neptunium en relatif presence d’uranium a 6t6 de 100,02 pour cent avec un &art t de 0,13 pour cent et le rendement d’un &talon d’uranium en p zcede neptunium a ttC de 100,03 pour cent avec un &art type relatif de 0,13 pour cent.

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REFERENCES G. A. Rechnitz, Controlled Potential Analysis, p. 68. Macmillan, New York, 1963. L. G. Farrar, P. F. Thomason and M. T. Kelley, Anal. Chem., 1958,30,1511. W. D. Shults and L. B. Dunlap, ibid., 1963,35,921. W. R. Mountcastle, Jr., L. B. Dunlap and P. F. Thomason, ibid., 1965,37, 336. R. W. Stromatt, Analysis for Neptunium by Controlled Potential Coulometry, U.S. At. Energy Comm. Report HW-59447,1959; Anal. Chem., 1960,32,134. 6. H. C. Jones, Automatic Coulometric Titrator, ORNL Model Q-2005, Electronic Controlled Potential, Methods l-003029 and g-003029. U.S. At. Energy Comm. Report TID-7015, Sec. 1,1959. 7. M. T. Kelley, H. C. Jones and D. J. Fisher, Anal. Chem., 1959,31,956. 8. R. J. Jones, Selected Measurement Methods for Plutonium and Uranium in Nuclear Fuel Cycle, Method 1.302. U.S. At. Energy Comm. Report TID-7029,1963. 1. 2. 3. 4. 5.

Talattta. 1967. Vol. 14. PP. 1360 to 1362. Pergamon Press Ltd.

Printed

in Northern

Ireland

Application of isotopic exchange for the determination of tin in nickel (Received 20 March 1967. Accepted 11 July 1967) RecEEny a method was described for the determination of several impurities, namely co per, .g. . arsenic, antimony, bismuth and zinc, in nickel cathodes .isa In further experiments the posse lllty of separating tin from the nickel matrix by isotopic exchange has been investigated. The principle of radiochemical separation by isotopic exchange is based on the well-known fact that the exchange taking place between the dissolved radioactive ions of an element and its fairly insoluble precipitate is such that the major fraction of the radioactive ions will be eventually bound in the precipitate. In spite of the simple technique and speed of the process, isotopic exchange has seldom been applied in activation analysis for the separation of the components of the irradiated sample. Its application in connection with activation analysis was tried first by Sunderman and MeinkeS who studied the isotopic exchange between radioactive silver ions and inactive silver chloride. Recently Qureshi and Shabbii+ performed experiments on the radiochemical recovery of cobalt and antimony by means of isotopic exchange. Isotopic exchange seemed for several reasons to be particularly convenient for the separation of tin from irradiated nickel samples. It was found to be more effective, the lower the solubilitv of the inactive precipitate used for the exchange. In the case of tin, tin(IV) oxide seemed to be the most Metallic nickel dissolves ranidlv in nitric acid. takine onlv l-2 min in hot nitric suitable pm&hate. acid, while inhydrochloric or sulphuric acid a long ti’me is required for diss%lution. On the other hand the solubility of tin(IV) oxide in nitric acid is sufficiently low to obviate precise neutralization of the solution or removal of nitrate ions, and because the metals which form hydroxide precipitates are less likely to be bound on its surface good selectivity can be achieved. EXPERIMENTAL The experiments were performed with the insmSn isotope (9.5 min half-life). The irradiations were carried out in the uneumatic facilitv built into the core of the VVR-S reactor. The stoppered small danamid capsule’containing the sample was put into an outer danamid ampoule, then irradiated for 3 mm. After irradiation, conveying the sample to the laboratory and unpacking it took about 45-60 sec. lnsmSn was quantitatively determined by measuring the 0.33 MeV photopeak intensity. For the measurements a 3 in. x 3 in. Tl-activated NaI crystal and 256-channel pulse-height analyser were used.