FR2643059A1 - PROCESS FOR THE SELECTIVE SEPARATION OF IODINE BY CHROMATOGRAPHY FROM ACUTE AQUEOUS SOLUTION - Google Patents

Abstract

a) Process for the separation of iodine by chromatography from an acidic aqueous solution. b) Process characterized in that an oxidant is added to the solution in at least a stoichiometric amount and, in order to retain the iodine in elemental form, the solution is sent to a macroporous polymer without functional groups. c) The invention relates to a process for the selective separation of iodine by chromatography from an acidic aqueous solution.

Description

Process for the selective separation of iodine by chromatography from

  The present invention relates to a process for the selective separation of iodine by chromatography from an acidic aqueous solution which contains iodine at various degrees of oxidation and in which dissolved state of other elements in the form of salts, in particular from a solution containing nuclear fuels and / or fission products in nitric acid, the process by which the solution is sent to an adsorbent for retain iodine and elute the iodine adsorbed with an eluent The separation of iodine plays an important role especially in the preparation of fission products for nuclear medicine, as well as in the reprocessing of nuclear fuel In this case, the iodine consists of a mixture of isotopes of iodine, mostly radioactive, with a high

  risk potential in the event of release.

  So far, Iodine is being removed

  elementary process solutions to boiling.

  This elimination is facilitated by the introduction of a stream of air. This method has the disadvantage that other fission products are volatilized and expelled from the solution, in the form of vapors or aerosols, which complicate the process.

purification of the rejected gases.

  It is furthermore possible to extract the iodine by means of organic solvents, for example carbon tetrachloride or benzene. The disadvantage of such a process lies in the fact that it is necessary to use flammable and generally very toxic chemicals, and that in particular the mixing and the subsequent separation of the phases require a high cost of equipment on the scale. industrial. In radioactive solutions, the iodine fission product can react with organic solvents, to give organic iodinated compounds

difficult to eliminate.

  Another possibility for the separation of iodine from organic solutions is chromatographic separation of the iodide anion on

  appropriate anion exchangers.

  The disadvantage of this method is that the iodide can not be separated sufficiently selectively from a salt mixture. In this process, the anion exchanger also

in other anions than iodide.

  The object of the invention is to avoid the disadvantages mentioned and in particular to provide a selective and efficient method, simple to implement, for the separation of iodine. This must not be hindered by the presence of foreign salts in the solution. Iodine must also be able to be

recovered in pure form.

  The object is achieved according to the invention by a process for the selective separation of iodine by chromatography from an aqueous acidic solution which contains iodine at various degrees of oxidation and in which the dissolved state is present. other elements in the form of salts, in particular from a solution containing nuclear fuels and / or fission products in nitric acid, by which process the solution is sent on an adsorbent to retain iodine and is eluted with the adsorbed iodide using an eluent, characterized in that the oxidant is added to the solution in an amount at least stoichiometric and to retain the iodine in elemental form, the solution is sent to a

  macroporous polymer without functional groups.

  According to a feature of the invention,

  the pH of the solution is between 3 and 0.

  According to another characteristic of the invention, nitrites, hydrogen peroxide or acid are used as the oxidant.

concentrated nitric.

  According to another characteristic of the invention, it is used as a polymer

  macroporous, a polyacrylate and / or a poly (styrene

  divinylbenzene). According to another characteristic of the invention, the iodine is eluted with aqueous solutions containing H 2 SO 3, bases or organic solvents. According to the invention, an oxidant is added to the solution containing iodine. Nitrates and hydrogen peroxide are particularly suitable as an oxidant. These oxidants pass at least a portion of the iodine at other oxidation levels, the degree of oxidation 0, that is to say in the elemental form. Thanks to the oxidant, the iodide ions present in the solution are oxidized and the

iodate ions are reduced.

  The solution probably treated in this way is sent according to the ivention on an adsorbent consisting of a macroporous polymer without functional groups. Elemental iodine is then adsorbed, while anions and cations are not retained. Due to the separation of elemental iodine, the equilibrium between elemental iodine and iodine at various degrees of oxidation is further displaced in the direction of elemental iodine, so that iodine is retained practically in total on the adsorbent, even if in the solution previously treated, it does not

  found only partially in elementary form.

  For carrying out the process according to the invention, it is essential that the solution containing iodine has a clearly acidic reaction. Preferably, the pH is adjusted to between 3 and 0. The process according to the invention can also be carried out in very strongly acidic solutions, for example in 7-8 M nitric acid solutions. nitric acid, the addition of another oxidant is superfluous because nitric acid

  highly concentrated is itself an oxidant.

  As the macroporous polymer, a polyacrylate or poly (styrene-divinylbenzene) without functional groups can be successfully used. The polymer is used in the form of a granular product, for example having

grains between 0.1 and 1 mm.

  It is advantageous to use the polyacrylate matrix marketed under the trade name SM 7 by the company Bio-Rad, in M nich. The firm Bayer-Leverkusen markets under the name

  Lewatit 1023 a poly (styrene) adsorbent

  divinylbenzene) charged with tributyl phosphate (TBP), which is also advantageously usable after the removal of TBP by washing. Some products

  similar products are placed on the market by the firm Bio-

  Rad, under the designations SM 2 and SM 4.

  In all these products, iodine is retained almost exclusively in elemental form. The adsorbed iodine can be eluted by aqueous solutions containing H2SO3 with water or mineral acids as a solvent, or by basic media such as NH40H solutions or alkaline hydroxide solutions. Elution may further be carried out with an ammonia solution or a sodium hydroxide solution containing H 2 O 2. Another possibility is to carry out the elution with organic solvents, such as for example benzene,

  chloroform or carbon tetrachloride.

  Since according to the invention, the adsorption of ionogenic species can be practically excluded, the presence of dissolved salts

  does not interfere with the retention of iodine.

  An essential advantage of the process according to the invention when it is used for the preparation of the fission nuclide for nuclear medicine lies in the fact that it is possible to selectively and efficiently separate and isolate in chemically pure form from iodine present in process solutions at relatively low concentrations. Iodine separated in this way can be reused, for example in the form of

therapeutic preparations.

  The invention is illustrated in greater detail in

  using the descriptive and non-limiting examples

after.

Example 1

  To a solution of 1M nitric acid was added potassium iodide and sodium nitrite dissolved in water, as well as 123I as a radioactive indicator. The concentrations of iodide and nitrite were each 5 * 10-3 mol / l. Two glass columns of the same dimensions (internal diameter 9.7 mm) were packed 100 mm high, respectively, with granular polyacrylate (SM 7, firm Bio-Rad) and poly (styrene-divinylbenzene) (Lewatit). 1023, firm

  Bayer). The particle size was 0.2 to 0.4 mm.

  We sent the solution of iodide upwards to

through the glass columns.

  The ratio of the amount of iodine passed through the columns to the one that was retained was established by comparative measurement of the activity of 123I. The figure shows the variation of the proportion of iodine which has passed through the columns (in%) as a function of the respective degree of charge (solution

added in ml).

  From the figure, it can be seen that in the case of feeding with 80 ml of solution, corresponding to a quantity of iodine of 50 mg, the iodine

  all adsorbed on the SM 7 column.

  The same result was obtained by previously stirring the solution with tributyl phosphate (TBP) in kerosene and then separating it with

new organic phase.

Example 2

  The high selectivity of the process according to the invention could be confirmed by subsequent tests in the presence of isotopes of radioactive fission products 144Ce, 95Zr and 106Ru. The tests were carried out by adding KI, NaNO2 and the fission product markers mentioned, to a solution of 3M HNO3. The concentrations of iodide and nitrite were each 10-3 mol / l. 25 ml of such a solution was sent in each case, as in

  Example 1, through two columns packed with SM 7.

  By means of comparative activity measurements,

  the retention of the different nuclides was calculated.

  The experimental conditions and the results obtained are summarized in the following table.

Board:

  Column internal diameter 9.7 mm Amount of adsorbent 1 g Bed volume 3.3 ml Loading speed 50 ml / h Adsorber particle size 0.2- 0.4 mm HN03 concentration Wash acid 3 moles / 1 Nucleotide Activity Activity Retention solution in the effluent (pulse / (+ 10 ml of acid s) washing Test i: I2 (123I) 750 nd> 99.9%

l06Ru 635 45i n.e.

gsZr 532 382 n.e.

44Ce 780 545 n.e.

  Test 2: 12 (123I) 920 n.d.> 99.9%

l06Ru 762,548 n.e.

Zr 833 589 n.e.

144Ce 791 562 n.e.

  (nd .: not detectable) In carrying out the tests, it was determined that: - The efficiency of the iodine separation of nitric acid solutions evolves in parallel with the formation of elemental iodine; it is carried out more rapidly than the concentration of HN03 is high. In the presence of HNO3 7 M, the formation of I2 takes place within a few minutes. - By addition of sodium nitrite or in the presence of NO2, the formation of I2 takes place almost spontaneously in the studied range, between 0.01 and 7 M. - When using adsorbents whose size of particle is in the range of 0, 2 to 0.4 mm in diameter or less in no way detract from the retention properties of charge rates of up to 30 column volumes per hour. - There was no evidence of a decline in iodine retention in the presence of organic contaminants such as TBP or kerosene, given their

solubility in HN03.

Claims (4)

  1 ') Process for the selective separation of iodine by chromatography from an aqueous acidic solution which contains iodine at various degrees of oxidation and in which other elements in the form of salts, in particular from a solution containing nuclear fuels and / or fission products in nitric acid, by which process the solution is sent onto an adsorbent to retain iodine and eluted at iodine adsorbed with an eluent, characterized in that an oxidant is added to the solution in an amount at least stoichiometric and to retain the iodine in elemental form, the solution is sent to a macroporous polymer without functional groups. 2 ') Process according to claim 1, characterized in that the pH of the solution is included between 3 and 0.   3 ') Process according to Claim 1, characterized in that nitrite, hydrogen peroxide or acid are used as the oxidant. concentrated nitric.   4 ') Process according to claim 1, characterized in that macroporous polymer is a polyacrylate and / or a poly (styrenedivinylbenzene). Process according to Claim 1, characterized in that the iodine is eluted with aqueous solutions containing H 2 SO 3, bases or organic solvents.