Extraction trivalent

SANEX 3 used the 2,6-Z) -(5,6-dialkyl-1,2,4-triazine-3-yl)pyridine family of extraetants eontaining the propyl group, whieh are able to selectively extract trivalent actinides from Imoldm EINO3 [53,78]. The extractant was 0.04mol dm in a mixture of 70%/30% TPH/octanol. A flow sheet based on this solvent has been tried and is shown schematically in Fig. 12.21 the results are given in Table 12.13. The feed was an... 

V,. V -l )imethyl-/V,/V -dioctyl hcxylcthoxymalonamidc, used in the DIAMEX process, which extracts trivalent metallic cations from highly acidic feeds by solvation, thus avoiding any adjustment of the acidity of PUREX raffinates. 

To increase the distribution ratios, a solution of lithium nitrate 1M was used. This salt, which has a common anion with europium and americium to be extracted but a cation which is usually negligibly extracted by other calixarenes, should increase the distribution ratios according to the relation Du = A (JU "[N03- ". It seems that these calixarenes, as several nitrogen ligands do, present a certain affinity for this lithium cation. The lipophilic dicarbollide anion (BrCosan), which is known to facilitate cation extraction, was implemented and led to a strong increase of the extraction of cations from 10 3 M HN03 solutions. Under these conditions, only thiopicolinamide was not able to significantly extract trivalent actinides.187... 

CH2CH2— but was little changed when X was varied from —CH2— to —CH=CH—, Dihexyl Ar,AT-diethylcarbamoylmethylenephosphonate (DHDECMP) has been used to extract trivalent ions from HAW. After back extraction with nitric acid or carbonate solution the lanthanides... 

Diketones. Beta-diketones such as acetylacetone, benzoyl-acetone, and isopropyltropolone are well known for their applications in analytical extraction of actinides. These compounds are weak acids due to tautomerization thus they can act as cation exchange extractants. Trivalent actinide [M(III)] extraction by the reagent (HA) at low aqueous acid concentration where the compound behaves both as cation exchanger and coordinator probably follows the reaction... 

Several methods were proposed for Pu-U partitioning which are not based on a reduction of plutonium to the less extractable trivalent state. The separation is achieved by either forming aqueous PuH complexes which have a low solubility in the TBP-hydrocarbon solvent or by saturating the organic solvent with uranium, which depresses the extractability of plutonium. 

Figure 2 shows conclusively that DHDECMP can extract trivalent as well as tetravalent and hexavalent actinides from moderately concentrated nitric acid solutions. The valence (III) actinides, Am, Cm, and Cf, have distribution coefficients greater than one above 1.5M HNO3, while valence (IV) and (VI) actinides have values greater than one above 0.5M HNO3. In addition, DHDECMP shows very favorable back extraction or stripping characteristics below 0.3M HNO3. Pu(IV) polymer formation undoubtedly occurred in low-acid measurements and may account for the low distribution coefficients. 

In these extractants, HNO3 interaction with the extractant occurs with the carbamoyl portion of the molecule (Horwitz etal. 1981), leaving the solvating phosphorus portion of the molecule to interact with the metal ion. These compounds are indeed more efficient extractants of the trivalent metal ions from acidic solutions, able to extract trivalent actinide and lanthanide ions from relatively dilute nitric-acid solutions. Horwitz et al. (1981) have studied the separation of the lanthanides and trivalent actinides from Am to Fm (table 2) using dihexyl-N, N-diethylcarbamoyl-methylphosphonate (DHDECMP) and aqueous nitrate solutions. Steadily decreasing distribution ratios are observed for the lanthanides, but nearly constant D s are found for the trivalent actinides. Group separation does not appear feasible while interlanthanide (but probably not interactinide) separations are possible. However, substitu-... 

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