DE1533054C - Process for the production of polonium - Google Patents

Description

The invention relates to a process for the production of polonium by means of neutron irradiation is formed from bismuth or from bismuth compounds.

Polonium 210 is formed by neutron irradiation of bismuth 209 or a bismuth compound. When irradiated, the bismuth is converted into its radioactive isotope Bi 210, which by / J decay passes into polonium 210.

To obtain the in the irradiated bismuth ίο When the polonium is formed, the bismuth is generally dissolved in a hydrochloric acid solution and the polonium then extracted with a suitable organic solvent. Another procedure exists in that one dissolves the irradiated bismuth in a hydrochloric acid solution and the polonium from this Solution "extracted" by adsorption on copper elements and from these by distillation in the Vacuum desorbed.

After this relatively complicated process, however, only a small proportion of the polonium formed can be be won.

It has also been suggested that this be in the polonium-bismuth mixture to separate contained polonium by dissolving this mixture in a hydrochloric acid solution and then the obtained "Bringing solution into contact with ion exchange resins, which adsorb the polonium and bismuth. The "desorption of bismuth is then achieved with concentrated hydrochloric acid, and that of polonium." with 'concentrated nitric acid.

However, this method has numerous disadvantages, which are essentially due to the application of Based on ion exchange resins. The ion exchangers are expensive materials, their service life for this application is limited by the fact that it is degraded or degraded by the action of radiation. to be changed. Also, their radiolysis products end up in the final as contamination Polonium solution. .

The aim of the invention is therefore a process for the production of polonium which has these difficulties bypasses, namely by using activated carbon as an adsorbent, i.e. by using it a material that is relatively cheap and practically does not decompose when exposed to radiation or changed and which also does not react with the acids used for desorption.

The method according to the invention for the production of polonium from a mixture with bismuth is therefore essentially characterized in that you * this mixture in a solution of a strong Dissolves mineral acid, brings the resulting solution into contact with activated carbon and the desorption of the polonium adsorbed on the activated carbon with an acidic solution.

The solution of a strong mineral acid used to dissolve bismuth or its compounds is preferably a solution of nitric acid with a normality between 0.5 and 2N and preferably in the region of 1N; however, other acid solutions can also be used, such as, for example, a solution of hydrochloric acid with a normality between 0.5 and 2 N and preferably in the region of IN. · ^Ö5

The kinetics of polonium adsorption on activated carbon was investigated; for a polonium concentration of 5.3 · ΙΟ " ⁷ g atoms per liter in N HNO3 medium, the values given in Table 1 below were obtained for the adsorbed amounts as a function of the contact time.

Table 1 Adsorption (%) Contact time (hours) 17.7 1 35 4th 48.8 6th 89.4 19th 93.5 ■ 24

As can be seen, a contact time of at least 19 hours is necessary for sufficient polonium adsorption to achieve.

From the values obtained one can derive the equation for the adsorption rate, and you get:

C = 100 (1-e 0- ¹¹³³ O

with C = adsorbed fraction in% and
/ = Contact time in hours.

The desorption of the powdered activated carbon (with a grain size that is preferably between 500 and 2000 μ) of retained polonium can be effected by oxidation with concentrated nitric acid.

Desorption can also be achieved in that the activated charcoal loaded with polonium is used brings into contact with metallic silver in a hydrochloric acid solution; in the course of a certain During contact time, the polonium migrates from the charcoal to the silver.

Finally, the desorption of the polonium can also be achieved by adding the activated charcoal with a solution of nitric acid with a normality that is advantageous in the area of 6 N, washes or treated, whereby all of the adsorbed polonium are recovered can.

The adsorption process should be carried out in a vessel that adsorbs as little polonium as possible. For this purpose, after various studies, resistant glass of the Pyrex type was selected because it has a lower adsorption capacity for polonium than materials such as polytetrafluoroethylene or polyvinyl chloride. After 19 hours of contact of a normal nitric acid solution of polonium with 4.6 · 10 ~ ⁷ gatoms of polonium per liter with one of these materials, the following adsorptions were observed:

4.2% Pyrex glass,
5.4% polytetrafluoroethylene,
17.5% plasticized polyvinyl chloride.

It follows that when working in a vessel made of Pyrex glass, only a small percentage of polonium is adsorbed by the vessel.

The activated carbon granules are comminuted in such a manner that their particle sizes are preferably between 2 and ⁵ / io mm; this coal, crushed in this way, is washed with 3N nitric acid, several

J533 054

Times rinsed with distilled water and then dried before using it for adsorption.
The adsorption was investigated at different pH values and different polonium concentrations; the results obtained for a contact time of 19 hours are summarized in Table 2 below:

all in all table 2 2.5 · ΙΟ "' Adsorption of polonium in% all in all 3- 10 " ³ of activated carbon 89.2 of activated carbon 86.5 75.6 74.7 on glass 85 63.4 on glass 42.2 80 Initial concentration of polonium in gAtom per liter 4.2 64.9 74 10.9 57.4 PH 81.7 9.8 65.6 68.3 21.2 33.7 0 80 14.4 62 75.9 16.6 30.7 1 86 19.7 47.2 78 34.6 54.8 2 70.8 32.8 66.7 77.4 45.2 60.6 3 74.4 19.3 55.8 78 23.2 50.4 4th 71.2 15th 45.1 71 16.8 30.2 5 29.3 38.2. 27.6 6th 33 40.8 7th 8th

From this table it can be seen that an adsorption maximum at pH = 0 and another maximum exists at pH = 4 to 6.

To obtain the polonium that is formed during the irradiation of bismuth or its compounds, these (or this) are dissolved in a solution of strong mineral acid in a reactor channel after the irradiation. The acid can be, for example, nitric acid or hydrochloric acid, optionally with the addition of hydrogen peroxide: After dissolution, the solution obtained is brought into contact with activated charcoal for a sufficient time, which depends on the initial concentration of polonium, in order to ensure maximum adsorption of the polonium. This operation preferably takes place at ambient temperature instead of, ie at a temperature in the region of 15 to 2O ⁰ C. It is generally forced to carry out two operations, wherein it cancels the first in an adsorbed amount of 75% and the solution then again with Bringing activated carbon into contact, which can lead to an adsorption yield in the region of 100%.

The bismuth is not adsorbed by the activated carbon; solutions of Bismuth nitrate in N-nitric acid brought into contact with activated carbon for 24 hours. After several times Washing of the activated carbon with nitric acid could not do any in the resulting solution Traces of bismuth are found.

The invention is illustrated by the following description of a non-restrictive example for one way of carrying out the method according to the invention can be better understood.

example

From 100 g of bismuth irradiated for 270 days in a reactor channel, 1 curie of polonium could be obtained 210 can be obtained. The bismuth oxide is dissolved in a normal nitric acid solution and the solution obtained in contact with activated carbon with a grain size between 0.05 and 1 mm for 19 hours brought.

During this time, 75% of the polonium present in the solution accumulates (on the activated carbon). The amount of Wistnüt carried along is a maximum of 5 ppm (• limit, for analytical evidence). The enrichment factor F can easily be calculated, it is given by the equation:

F =

(KL)

\ Bl /End

/ Po \

Ibt)

beginning

In this example, an enrichment factor of greater than or equal to 150,000 is achieved while values above around 2500 can hardly be achieved with the method that is usually used. the The starting solution is again brought into contact with activated charcoal for 19 hours, and one arrives at so for the recovery of the polonium residue and a total adsorption yield in the region of 100%. The desorption was achieved by oxidizing the powdered activated carbon with concentrated HNO3 performed.

Claims (4)

Patent claims: 1. Process for the production of polonium from a bismuth and polonium containing Mix by dissolving this mixture in a solution of a strong mineral acid and Separation of the polonium by selective adsorption, characterized in that that the bismuth and polonium containing solution to separate the polonium with Bringing activated carbon into contact and the activated carbon for desorption of the adsorbed polonium treated with an acidic solution. 2. The method according to claim 1, characterized in that the solution is a strong Mineral acid is a nitric acid or hydrochloric acid solution, the normality of which is between 0.5 and 2N and preferably in the region of 1N. i ODD UO4 5 6 3. The method according to claims 1 or 2, activated carbon in hydrochloric acid solution with metallic characterized in that the loaded silver is brought into contact. Activated carbon up to a grain size between 2000 5. The method according to claims 1 or 2, and 500 μ crushed and with more concentrated characterized in that the loaded Nitric acid oxidizes. 5 activated carbon with a solution of nitric acid 4. The method according to claims 1 or 2, a normality between 5 and 7 N and before characterized in that the loaded one washes preferably in the region of 6N.