DD217190A1 - METHOD FOR SEPARATING STRONTIUM AND CAESIUM FROM REPRODUCTION SOLUTIONS - Google Patents

Abstract

The invention relates to a process for the rapid and selective removal of Sr and Cs from spent nuclear fuel element reprocessing solutions by extraction with crown ethers and has the object of enabling the reuse of the crown ether. The aqueous waste solution is adjusted to a p H value between 2 and 4 and mixed with Picrat. The extraction is carried out with crown ethers of the type R-18-crown-6 in chloroform or n-alkanes, the back extraction of Sr and Cs from the organic phase with 2-4 N HCl or HNO3. Thereafter, the organic extraction mixture can be used immediately.

Description

Process for the separation of strontium and cesium from reprocessing solutions '. ';

Field of application of the invention · <<

The invention relates to a process for the rapid and selective separation of strontium and cesium from spent nuclear fuel reprocessing solutions by extraction with crown ethers.

Characteristic of the known technical solutions

Crown ethers are known to have a high complexing constant over alkali and alkaline earth metals. Investigations were therefore carried out on the use of crown ethers for the extraction of strontium and cesium. As the organic phase, for example, 24-crown-8 solutions were used (designations according to C.J. Pedersen, J. Am. Chem. Soc (1967), 7017) in QCl ₄ or kerosene with different additions of tributyl phosphate or di-2-ethyl-hexylphosphoric acid. "The aqueous solutions contained 0.001 M CsUO ₃ or Sr (NO-J ₂ different in nitric acid, strength · in some cases In addition, KNOp was added (Separation Science and Technology (1979) 395). Also, the use of picrate was studied (J. Am. Chem. Soc., 3, 4674 (1971)), but the distribution coefficients for the alkali metals were extremely small. The extraction of alkaline earth metals from nitric acid solution was carried out _using dicyclohexyl-18- _{theory _6} in dichloroethane (Radiochimija Nr * 2 / 1-982, 214). · The maximum of the extraction

100480

is achieved at 1.5 - 2 M HNO. The back extraction was carried out with excess water at elevated temperature.

However, because of the high cost of the crown ethers, there has been no technical use for the separation of strontium and / or cesium. ν

Object of the invention

The object of the invention is the rapid and selective separation of strontium and cesium from waste solutions of spent fuel reprocessing.

Explanation of the essence of the invention

The invention has for its object to provide a method for the separation of strontium and cesium from such solutions, which allows the reuse of the crown ethers used.

The erfindungsgeraäße method consisting of the steps

Adjusting the aqueous solution to a pH between 2 and 4,

- Addition of Picrate and

- Extraction with crown ether

consists, is characterized in that are used as extractants crown ether of the type R-18-crown-6 in chloroform or n-alkaneij and the Rückextrakt ion of strontium and cesium from the organic phase with 2-4 K inorganic acids, preferably hydrochloric acid or nitric acid takes place.

Surprisingly, it was found _l9 that only the back-extraction with inorganic acids in the aforementioned concentration range both leads to complete back-extraction of strontium and cesium as well as for immediate reusability of organic ex tr ac ti ons mixture used · When using eg stronger acids is the reusability of the organic extraction

· The multiple use of the extractant, but is a prerequisite for the practical applicability of the extraction with crown ethers. The concentration of the crown ethers in the solvent should be as high as possible; it is generally limited by its solubility. The phase ratio is 1: 1, but may · deviate from it. '

Strontium and cesium are separated in good yield within a few seconds in an extraction step. Since the reextraction also proceeds very quickly, the process according to the invention is suitable for rapid separation. The back - extracted components strontium and cesium can be separated in a known manner.

An elegant variant of the proposed method is the implementation as a membrane process: a solid permeable membrane carries on one side a solvent containing the crown ether, on this side, the aqueous solution is passed with the components to be extracted, the other side of the membrane is with a 2-4 N inorganic acid in contact "strontium and cesium are transported into the acid via the membrane * The further separation can then again take place in a known manner.

The advantages of the invention are that the crown ethers used can be used repeatedly for extraction without further treatment. "This is further promoted by the fact that crown ethers are distinguished by high radiation resistance.

embodiment

250 ml of a cleavage product solution, which in addition to other cleavage product .ten-also 4.9.1O "3 mol / 1 cesium and 2.8.10" ³ mol / l strontium in

3 M KUOo contains, with sodium hydroxide solution to a pH of

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2,8 is added. Then enough natrium picrate is added so that the solution is 0.2 molar of Pierat. The extraction is carried out with 250 ml of a 0.1 M R-18-crown-6 solution in; chloroform by shaking in an extractor (shaking time 15 seconds). Wach'der phase separation, the organic mixture is treated with 200 ml of 4 J HGl and thus back-extracted strontium and cesium. The organic extraction mixture is then returned to the extractor without further treatment. The separation of strontium and cesium is carried out in a known manner · The extraction is very selective, the proportions of other cleavage products in the organic phase are less than 0.01% *

Claims (4)

Claim of the invention,. , 1. A process for the separation of strontium and cesium from reprocessing solutions of spent nuclear fuel, consisting of the adjustment of the aqueous solution to a pH between 2 and 4 »the addition of picrate and the extraction with crown ethers, characterized in that the extractant crown ethers of the type R-18-crown-6 in chloroform or n-alkanes are used and the back-extraction of strontium and cesium with 2-4 N inorganic acid takes place. 2. The method according to item 1, characterized in that hydrochloric acid or nitric acid are used for the re-extraction. 3 · Method according to item 1, characterized in that the organic mixture is used again after the re-extraction without further treatment as the extraction agent. 4. The method according to item 1, characterized in that the cleavage product solution on one side of a solid permeable membrane, which is coated with the crown ether-containing solvent, and the 2-4 N, inorganic acid is passed to the other side of this membrane _β