Isolation of carrier-free 233Pa from irradiated thorium nitrate

Reactor Science and Technology (Journal of Nucfear Energy. Parts A/B).

ISOLATION

1961. Vol. 15. pp. 47 to 49.

Pergamon Press Ltd.

OF CARRIER-FREE es3Pa FROM THORIUM NITRATE*

Printed in Northern Ireland

IRRADIATED

V. I. SPITSYNand M. M. GOLUTVINA (Received 13 November 1959) Abstract-A method is given for the isolation of carrier-free 233Pafrom thorium nitrate irradiated with slow neutrons. It consists of isolating *“Pa from the thorium nitrate solution by sorption on a MnOo precipitate; extracting the cupferron complex of protactinium with amyl acetate; re-extracting the protactinium into aqueous citric acid; and decomposing the citrate complex by oxidation with nitric acid. Good separation from a!- and p-emitters was achieved. The isolated radioisotope was identified by its half-life period. The method will be found useful for obtaining carrier-free *SSPa,which can be employed as a tracer in chemical studies on protactinium, and in investigations of the extraction of protactinium from natural raw materials and of the separation of zsrPa from thorium during the preparation of *SsU.

selective when MnO, is precipitated from a strongly acid solution. Citric acid and fluorides interfere by THE following process is used to obtain 233Pa from forming stable, soluble complexes with the prothorium : Ptactinium. To study the sorption of =Pa by pre232Th(n,y)233Th‘t = 12 ‘?1 mitt+ 233Patt ==2i.odilys cipitated MnO,, we carried out the following experi=YJ If ... ments with freshly irradiated thorium nitrate, which The neutron activation cross section of 232Th is(l) was dissolved in 7-N nitric acid and diluted to a 7.33 + 0.12 barn. The 233Pa so obtainedf2) is usually specific activity of ~5 x lOA counts mine1 ml-l. An contaminated with thorium and va?ious radioisotopes end-window counter was used having a mica window derived from 233U by neutron-induced fission. The of 1.8 mg crnd2 thickness. literature contains several pap&s’3-5) dealing with The solution (3 ml) and 5 per cent manganese the isolation of 233Pa. sulphate solution (0.5 ml) were heated on a water-bath We have based our work on the papers of MADDOCK to 80°C. The addition of 0.5 per cent potassium and MILES.@~~) Before the method of these authors permanganate solution (0.8 ml) precipitated MnO,, could be adopted, we had to carry out detailed in- which was coagulated by heating for 20 min. After vestigations to determine suitable conditions for each the addition of more potassium permanganate solution stage of the purification process. (0.8 ml), the precipitate was separated by centrifuging and dissolved in 7-N nitric acid (1 ml) containing a 2. INVESTIGATION OF THE MANGANESE small amount of sodium nitrite. The yield of MnO, DIOXIDE PRECIPITATION was 1 mg per ml of solution. It was shown that 97 Protactinium was separated from thorium and per cent of the initial activity was adsorbed by the zirconium by sorption on a precipitate of manganese precipitate. dioxide, a phenomenon first described by GROSSE and In subsequent experiments the purification was AGRUSS.@)Manganese dioxide was prepared in one improved by carrying out three precipitations of the of the following ways: MnO,, the yield being increased to 4.4 mg per ml of 2KMn0, T 3MnS0, f 2H,O = solution. 98 per cent of the initial activity was adsorbed by the precipitate. = 5Mn0, f K,SO, + 2H,SO, or 3. INVESTIGATION OF THE CUPFERRON KCIO, + 3MnS0, -t 3H,O = EXTRACTION Amy1 acetate extraction of the cupferron complex = 3Mn0, +- KC1 j 3H,SO,. The sorption of protactinium on MnO, is efficient of protactinium was employed to free 233Pafrom trace and almost independent of the conditions of pre- impurities sorbed by the MnO,. The precipitated cipitation; sorption is most complete and most MnO,, prepared as described above and dissolved in hot concentrated hydrochloric acid, was treated with * Translatedby G. RYBACK from Atontna~a Energiyu 8, 117(1960). an equal volume of a saturated aqueous solution of 1. INTRODUCTION

47

48

V. I.

TABLE1.--AMyL

ACETATE EXTRACTION OF =‘pa

SPITSYN

and M. M. GOLUTVINA

CUPFERRONATE

FROM 6N HYDROCHLORIC ACID

@activity *of amyl acetate phase (% of initial activity)

p-activity of aqueous phase (% of initial activity)

107 113 111 76 80 116

2 3 4 1 1 5

Average 100

Average 3

4. DISCUSSION

cupferron containing a small quantity of hydroquinone as stabilizer. The mixture was then shaken with an equal volume of amyl acetate, the volumes of the two phases being measured before and after shaking. The results given in Table 1 show that protactinium cupferronate is satisfactorily extracted by amyl acetate from 6-~ hydrochloric acid. To re-extract the protactinium into aqueous solution, the amyl acetate solution was shaken for 5 minutes with an equal volume of 1-Mcitric acid. On heating the mixture on the water-bath for 40 min the cupferronate decomposed and the protactinium passed into the aqueous phase, in which it formed a stable complex with citric acid. When cold the mixture was TABLE 2.-sEPARATION

OF ‘%3

FROM a-m

DURING

ISOLATION FROM IRRADIMED THORIUM NlTRATE

u-activity of precipitate (% of initial activity)

MnO, precipitation

2

1 I

First precipitation Second precipitation Third precipitation

I

43 14 8

again shaken for 5 minutes, and the volumes and activities of the separated-phases were then measured. It was shown that 85-90 per cent of the activity originally present in the amyl acetate solution passed into the citric acid solution. The latter was then repeatedly treated with hot concentrated nitric acid.

42 10 5

It was shown in the course of our work that most of the stages in the isolation of WPa are successful only if the mineral acid concentration is high (26-7 N). When the acidity was lowered to 3-35 N, the results deteriorated considerably, adsorption on the walls of the vessel increased, and the experiments became poorly reproducible. The degree to which the =Pa was purified of a-emitters (e.g. uranium and thorium) present in the original solution was determined, using a zinc sulphide crystal scintillation counter. The results (Table 2) show that the main separation from a-emitters occurs in the course of the three precipitations of the MnO,, and is completed at the amyl acetate stage (the amyl acetate phase has zero activity). On the basis of our experiments the following method has been developed for the isolation of carrier-free sssPa from irradiated thorium nitrate. 5. EXPERIMENTAL METHOD A solution of freshly irradiated thorium nitrate in 7-N nitric acid was mixed with 10 per cent manganese sulphate solution (O-2ml per 1 ml of the thorium solution) and heated to 80°C on the water-bath. 1 per cent potassium permanganate solution (O-5ml per ml of the thorium solution) was stirred slowly in. The MnO, precipitate was coagulated by heating on the water-bath for 20 min, centrifuged off, and dissolved in hot concentrated nitric acid containing a small quantity of sodium nitrite. The solution so

TABLE 3.--ISOLATION OF ‘*‘~a FROM IRRADIATED THORIUM NITRATE (Original

solution in

7-N

nitric acid; yield of MnO, precipitate 4.4 mg per 1 ml of solution) Activity (% of initial activity)

Three-fold MnO, precipitation Sorbed by precipitate

Motherliquors

Extraction with amyl acetate from

Amy1 acetate phase 1

Aqueous Phase

6-~

HCl

Remaining on walls of vessel

Reextraction with M citric acid

Isolation of carrier-free

rasp, from irradiated thorium nitrate

49

with occasional shaking. The aqueous phase containing the 233Pa was separated when the mixture had cooled. 6. RESULTS

0 7

15 23

31

39

Time, FIG.

47

55

63

71

79

0-r

dw

1.--,&decay curve of the isolated *srPa.

obtained was diluted with an equal volume of water, and the precipitation of MnO, repeated twice. The final MnO, precipitate was dissolved in hot 6-N hydrochloric acid. To this solution was added an equal volume of cupferron solution (7 g cupferron and 0.2 g hydroquinone dissolved in and made up to 100 ml with 6-N hydrochloric acid, and filtered), and the liquids after being well mixed were transferred to a The vessel which originally separating funnel. contained the solutions was washed out with two portions of amyl acetate (total volume equal to the combined volumes of the acid and the cupferron solutions), which were then added to the separating funnel. After shaking for 5 minutes the phases were allowed to separate. The protactinium was re-extracted from the organic phase by an equal volume of I-M citric acid solution, the mixed organic and aqueous phases being heated on the water-bath for 30 minutes

4 410

pp. 1

Table 3 shows the results obtained by the above method. The relative mean square deviation of the activity measurements was $3 per cent. It was possible to extract up to 70 per cent of the 233Pa activity from samples of freshly irradiated thorium nitrate. The p-decay of the isolated radioisotope (Fig. 1) confirms its identity; the observed half-life of 27 days agrees well with the value in the literature. The extent to which the protactinium is freed from fission fragments has not been specially determined, but the measured half-life suggests that no significant amounts of these are carried through the purification process. REFERENCES 1. Neutrorz CrossSections. BNL-325, New York (1958). 2. STROMINGERD., HOLLANDERJ. M. and SEABORGG. T., Rev. mod. Phys. 30, 585 (1958). 3. FUDGE A. J. and W~~DHEAD J. L., Analysr 81, 417 (1956). 4. FUDGE A. J. and W~~DHEAD J. L., Chem. Industr. 33, 1122 (1957). 5. GOBLE A. G. and MADDOCKA. G., 7-rms. Furuda,v Sot. 55, 591 (1959). 6. MADD~CK A. G. and MILES G. L., J. them. SOC.(Sup@.) 248 (1949). 7. MADDOCKA. G. and MOLESG. L., J. them. SOC.(SuppI.) 253

(1949). 5. GROSSEA. and AGRUSS M. S., J. amer. them. SOC. 57, 438 (1935).