CS216101B1 - Process for extraction of trivalent lanthanides and actinides from aqueous solutions - Google Patents

Abstract

Extraction method Isolation of trivalent lanthanides and actinides from aqueous solutions in the presence of metallodicarbolides. The invention relates to the chemical-technological issues of processing acidic waste solutions of the Purex process with the aim of isolating a common fraction of lanthanides and actinides from these solutions. This aim is achieved by extracting the mentioned elements with a solvent in which two extraction agents are dissolved, namely a two-donor organophosphorus reagent containing two functional groups P=0 or one group P=0 and one group C=0 and a metallodicarbolide. The advantage of the invention is the possibility of achieving sufficiently high partition ratios of trivalent lanthanides and actinides from Purex waste solutions without any preliminary treatment, very low losses of reagents into the aqueous phase and the possibility of selective re-extraction of cations from the organic phase.

Description

The invention relates to an extraction process for the isolation of trivalent lanthanides and actinides from aqueous solutions, in particular from acidic highly active waste solutions of the Purex process.

Separation of lanthanides and actinides from acidic aqueous solutions, especially from high-waste waste solutions after reprocessing of nuclear fuel, is still an unresolved problem. Separation of the isotopes americia and curia from active waste, however, represents a significant benefit in terms of long-term environmental protection and therefore, especially in recent years research into separation methods has been very intensive.

According to the prior art, the initially acidic waste solutions are de-acidified by denitration or neutralization and the trivalent element fraction is extracted from the medium of 0.1 = 0.5M HNO 3, optionally with the addition of high concentrations of solubilizers to the aqueous phase into an organic solvent containing e.g. (ethylhexyl) phosphoric acid, tributyl phosphate or organic amine. Due to the disadvantages of these processes, which include, in particular, the need to deacidify the starting solution in order to solve the problems of hydrolysable components dropping and to significantly increase the content of Li, Na, or Al ^y ions in the raffinate, other methods for isolating trivalent elements have been sought.

Processes using two-donor phosphororganic reagents containing two functional groups P = 0 or one P = 0 group and one C = 0 group have proven to be particularly advantageous for the extraction of trivalent actinides and lanthanides. Using these agents, it is possible to extract said elements directly from strongly acidic solutions and thus avoid the disadvantages mentioned in the previous paragraph. Dihexyl E (diethylcarbamoyl) methylphosphonate and dibutyl-4-diethylcarbamoylmethylphosphonate (hereinafter referred to as DHDECMP and DBDECMP) are most commonly used for extraction, see, e.g., L. D. Mc Isaac et al., Report ICP 1180, May 1979; Navratil J. D. and Thompson G. H., Nuclear Technology 43.136 (1979); N. 0. Schroeder et al., J. inorg. nuCl. Ohem. 42. 1029, (1990), UK Patent 1552,956, October 1979; Examples of the use of reagents with two functional groups? = 0 are contained, for example, in práci. K. Ohmutova and co-authors, J.inorg, nucl. Ohem. 42.897 (1980) and AM Rozen and co-authors, USSR Authentication 601971, September 1979. The methods proposed hitherto use solutions of the above reagents in a non-polar solvent such as carbon tetrachloride, chloroform, diisopropylbenzene and the like to extract trivalent elements. to the organic phase. The main drawbacks of all of the above procedures and the use of dual donor reagents can be summarized as follows:

- relatively high losses of raffinate reagents that led to the replacement of DBDECMP with more hydrophobic DHDECMP but even with this reagent, the solubility in 3M HNO 2 is close to 0.2 g / l

- the need to use concentrated reagent solutions in an organic diluent (30% reagent solutions in carbon tetrachloride are commonly used)

an increase in the partition ratio with increasing acidity of the aqueous phase and the associated necessity of re-extracting the trivalent elements into the aqueous phase 8 by low acidity. However, at low acidities of the aqueous phase, the trivalent elements are extracted by other organophosphorus compounds, which may be contained in the original preparation as impurities, or may be formed by radiolysis of the extract, so that reextraction can be made more difficult or impossible

the process does not, in principle, allow selective reextraction of the trivalent lanthanide fraction separately from the trivalent actinide fraction with the complexing agents contained in the aqueous phase, as is customary in other non-dual-donor separation processes, such as the Talspeak process. Conventional complexing agents are effective at low acidities of the aqueous phase, but under these conditions both fractions reextract, so that separation of one fraction from the other is not possible.

In order to isolate monovalent and divalent elements directly from acidic waste solutions after treatment of irradiated nuclear fuel with the Purex method, processes using solutions of metalodicarbolides in an organic solvent such as M. Kyrš,

S. Heřmánek, J Rais and J. Plešeks MS. author's certificate δ. 182 913, July 1980, optionally in the presence of organic compounds containing C-O-C groups, for example J. Rais, M. Kyrš and S. Heřmánek, cs. No. 153,933, June 1974. However, these processes have the disadvantage that the extraction of the trivalent elements is relatively inefficient and, in order to achieve sufficiently high partition ratios, the original solution of high-reactive products having an acidity of 3 moles / 1 HNO 3 must be diluted or denitrated six times. to an acidity of 0.5 / 1 HNO 4. A further disadvantage is that the proposed processes are not sufficiently selective, so that the isolation of the trivalent elements simultaneously extracts other elements such as cesium, rubidium, strontium and barium, of which cesium and rubidium in particular are difficult to elute from the organic phase after extraction. Thus, these processes using metalodicarbolides for the extraction of trivalent elements are limited to the case where the abovementioned interference elements have been preliminarily removed from the original high reactive solution, but this is in practice only a rare case.

The disadvantages of these processes are eliminated by the process according to the invention, which consists in using a mixture of a two-donor phosphorous organic compound containing two functional groups P = 0 as an effective extraction agent for the extraction of trivalent lanthanides and actinides.

Fe, Co, Ni, preferably cobalt, in an organic solvent.

Thus, in the process of the invention, the trivalent lanthanides and actinides are extracted into an organic solvent containing simultaneously a two-donor neutral phosphororganic reagent to form a positively charged complex with a trivalent metal cation and a hydrophobic anion of the metalodicarbolidide to provide electroneutrality of the organic phase. The extraction characteristics are quite different from the case of the extraction with the two-donor phosphorous reagent itself and with the raetalodicarbolide alone, which implies the following advantages of the proposed process. The process differs from the extraction with the two-donor reagent itself in that the acid-dependency of the partition ratio is just reversed, i.e. decreases with increasing acidity, which can be used to re-extract trivalent elements from the organic phase by increasing the acid concentration in the aqueous phase. It is also possible to use complexing agents for the selective reextraction of trivalent actinides from the organic phase, since at low acids the extraction is generally high 9 unconclexed ketones of the compounds are present in the organic phase. In particular, the process differs from the extraction with metallodicarbolide by the fact that there is no preferential extraction of cesium and rubidium ions, thereby substantially increasing the selectivity of the process in a favorable sense and further reducing the losses of the reagent (metallodicarbolide) from the leaving aqueous phase. Further advantages of the proposed process are the fact that the extraction by the reagents themselves, i.e. metalodicarbolides and dual donor reagents, in particular DBDiiCMP and DHDECMP, has been studied in detail before, so that their properties are well known.

The process can be advantageously used for extracting the group of rare earth elements by extraction method, in particular for treating acid leaches in mineral acids.

The reextraction can be carried out simply by increasing the acid concentration in the aqueous phase, thereby reducing the partition ratio and the transition of trivalent elements to the aqueous phase, or by using complexing agents in the aqueous phase, e.g. 0.1-0.25 mol / l sodium diethylenetriaminepentaacetic acid. If aqueous solutions of substantially different acidity than the acidity of the aqueous phase during extraction are used for reextraction, it is advisable to wash the organic phase, for example, with distilled water, without losing the components under consideration, to the aqueous phase before reextracting. .

The invention is illustrated by the following examples.

Example 1

From the aqueous phase containing 3 moles of HNO 3 / l, a micro amount of Su (IIX) and Am (III) was extracted with an organic solvent containing 0.04 moles of H ⁺ C 4 BgGip 4 Co ^- ^ / 1 and 0.06 moles DBDECMP / L in 60 % by volume of nitrobenzene and 40% by weight of carbon tetrachloride. The partition ratio, defined as the ratio of concentrations in the organic and aqueous phases, was equal to europium 32 and america 39 after equilibrium, while using DBDECMP alone, the partition ratio for europium was only 0.15 and H ⁺ J alone (CjBgHgCl) The concentration of europium was only 0.0006. The partition ratio of cesium mixtures of extracts under the conditions given in the beginning of the example was 0.06, while using H ^{+ 6} alone (CgE ^ ngClClgCoo at the same concentration was 6).

Example 2

The procedure was as in Example 1, except that H ^{+ 4} C 8 B 8 H 9 Br 2 gCo-J was used in the same molar concentration as in Example 1 and the acidity of the aqueous phase was 8 moles HNO 3 / l. . The partition ratio under these conditions suitable for reextraction was 0.54 for both europium and america.

Example 3

From the aqueous phase containing 3 moles of HNO4 / L, a micro-amount of europium was extracted with an organic solvent containing 0.04 moles of H ⁺ J (CgBgH4QCl71 and 0.06 moles of DHDECMP / 1 in nitrobenzene). Subsequent reextraction with an aqueous solution of 0.2M sodium salt of diethylenetriapentaacetic acid and lactic acid gave a partition ratio of less than 0.1.

Example 4 ·

From the aqueous phase containing 3 moles of HNO 4 / l, a micro-amount of europium was extracted with an organic solvent containing 0.04 moles of H ⁺ J 3 BgHgCl 3 · Co J / 1 and 0.06 mole DBDECidP / 1 at 1.24

-dichloroethane or chloroform. The europium partition ratio was 1,2-dichlorone when used. of ethane 25.5 and 9.05 in the case of chloroform.

Claims (1)

Method for the extraction isolation of trivalent lanthanides and actinides from aqueous solutions, characterized in that the elements are extracted with a mixture of a bi-donor phosphoric reagent containing two functional groups P = 0 or one P = 0 and one C = O, preferably dihexyl. diethylcarbamoylmethylphosphonate, with a metalodicarbolide of the general formula (I) Me (-) wherein X is halogen, y is 0 to 8 and Me is a trivalent metal from the group Pe, Co, Ni, preferably cobalt, in an organic i-solvent .