The use of the strong polydentate extractants, neutral (NOPCs, diphosphine dioxides and carbamoyl phosphine oxides) and acidic [poly-2-ethylhexylphosphonitrilic acid (P2EHPNA)] organophosphorus compounds, in recovery of transplutonium and rare-earth elements from the waste of the first cycle was considered. Compounds of the first group exhibit enhanced extractive power due to bidentate coordination and the effect of anomalous aryl strengthening, and those of the second group, because of no dimerization. The extraction constants of bidentate NOPCs are by a factor of 10(5) higher than the corresponding values for the strongest monodentate NOPCs, and the extraction constants of actinides(III) with P2EHPNA are by a factor of 10(8) higher than with DEHP. With the indicated extraction characteristics, TPEs can be recovered from solutions of any acidity without special treatment. Recovery procedures based on bidentate NOPCs were tested on solutions of high-burnup fuel.

A study has been made of distribution of highly extractable nitrosoruthenium complex RuNO(NO3)(3) (RuT) between aqueous solutions and tributyl phosphate (TBP) in n-dodecane. Short phase contact (similar to 30 s) was employed to minimize possible mutual conversion of nitrosoruthenium species, which takes place in the case of prolonged phase contact. The distribution coefficient alpha(RuT) is independent of hydrogen ion concentration and the presence of various salts in aqueous phase, i.e., RuT is extracted as nonelectrolyte. Experiments in which the TBP concentration was varied by dilution or binding TBP with nitric acid and uranyl nitrate indicates formation of trisolvate (as main complex characterized by extraction constant K-3 = 72) and disolvate (K-2 = 5). At high nitric acid and/or uranyl nitrate concentration, alpha(RuT) is insignificantly reduced, while solvate number decreases substantially. Probably, nitrosoruthenium tetranitrate, e.g., RuNO(NO3)(3) . HNO3 . TBP, and/or complex of RuT with uranyl nitrate is formed. The decontamination of valuable fuel components from ruthenium may be improved by a factor 10(3) by binding TBP with nitric acid and uranyl nitrate. Another way to reduce alpha(RuT) is to convert RuT into poorly extractable RuD form. The time of RuT half-conversion into RuD was found to be 15 min in the presence of HNO3, 9 min in the presence of uranyl nitrate, and 5 min at 50-60 degrees C(simultaneously alpha(RuT) decreases by an order of magnitude).

This paper studies the variation of the extraction capacity within a broad series of didentate organophosphorus compounds, from diphosphine dioxides to carbamoylphosphine oxides and phosphonates. The authors consider the disputed questions of the coordination of the actinides when carbamoyl compounds are used and they consider whether an effect of anomalous aryl strenghening exists in these systems. The compounds used are presented. The extraction of microquantities of americium and other actinides was performed from nitric acid media.

The effect is discussed of the structure of organic compounds of different classes on actinide element extraction. The interpretation of regularities observed in terms of statistical thermodynamics is given.

The extraction of americium(III) from nitric acid solutions with six diphosphine dioxides in the series R/sub 2/P(O)CH/sub 2/(O)PR/sub 2/--R/sub 2/P(O)CH/sub 2/(O)PPh/sub 2/--Ph/sub 2/P(O)(CH/sub 2/)/sub n/(O)PPh/sub 2/ (n = 1-3) was investigated. The distribution coefficients are the highest (100 at an extraction reagent concentration of 0.01 M and acidity 1 M) for tetraphenyl dioxide. It was found that in the region of low acidities, the dioxides form disolvates AmS/sub 2/(NO/sub 3/)/sub 3/ with Am, and at high acidities then form acidocomplexes HpMe(NO/sub 3/)/sub 3+p/ . 2S. The concentration and effective constants of extraction were determined. Their high value and the large chelating effect are evidence of a bidentate coordination of the dioxides to Am. It was shown that lengthening of the alkylene bridge of tetraphenyl dioxide leads to a large reduction of the extraction capacity. It was found that when the electronegativity of the substituents is increased (replacement of alkyl groups by phenyls), the extraction capacity of the dioxides relative to americium increases. Causes of this anomaly are discussed.