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Apparent formation constants of Pu(IV) and Th(IV) with two kinds of humic acids were determined in 0.1 M NaClO4at 25 ºC using a solvent extraction method with thenoyltrifluoroacetone in xylene. The acid dissociation constants of humic acids were also measured by potentiometric titration and used as the degree of dissociation for calculating the formation constants. The effect of solution conditions, such as the pH, the initial metal and humic acid concentrations, and the ionic strength, on the formation constants was examined. The obtained data were compared with the ones in the literature.

The complex formation constants of tetravalent plutonium ion with malonic and succinic acids in aqueous solution were determined by the solvent-extraction method. Also, by taking the known values of the solubility products, the hydrolysis constants and the formation constants, the experimental solubility data of plutonium in the presence of carboxylates were analyzed.

The separation of Am(III) and Cm(III) by countercurrent chromatography (CCC) was achieved using the liquid phase systems "diamide–hydrogenated tetrapropylene (TPH)–HNO3" following the optimisation of: (i) the compositions of the mobile (HNO3 concentration) and the stationary (nature of the diamide and its concentration in TPH) phases, (ii) column length and (iii) operating parameters of the CCC (flow rate of the mobile phase and rotation speed of the coil column). The following diamide extractants have been studied: (i) N,N´-dimethyl-N,N´-dibutyltetradecylmalonamide (DMDBTDMA), (ii) N,N´-dimethyl-N,N´-dioctylhexyl-ethoxymalonamide (DMDOHEMA) and (iii) N,N´-dimethyl-N,N´-dibutyldodecylethoxymalonamide (DMDBDDEMA). It is shown that these diamides can be used for the separation of Am(III) and Cm(III) by CCC. Increasing the column length leads to an increase of the stationary phase retention on the column while improving the Am/Cm separation. Increasing the speed of rotation of the centrifuge from 660 to 950 rpm also results in increasing the stationary phase retention but does not influence the resolution of the Am/Cm separation. Decreasing the flow rate of the mobile phase from 1.0 to 0.5 mL/min leads to a better resolution of Am and Cm separation. The best Am/Cm separation was achieved with systems based on DMDBDDEMA and DMDOHEMA in TPH using a two-layer coil column and an isocratic elution mode. The application of CCC makes it possible to separate the elements within 100 min: the Cm fraction contains 99.5% of Cm(III) and 0.6% of Am(III) inventories and the Am fraction contains 99.4% of Am(III) and 0.5% of Cm(III).

Summary The reactions between Am or Eu present in 0.1 M nitric acid solutions, alone or both together, with 0.25 M K3Fe(CN)6, were studied at room temperature. When Am was the only trivalent metal ion in solution, precipitation of AmFe(CN)6 occurs and the residual Am concentration is about equal to 0.95 mM. However, when Am initial concentration is less than the above specified value for AmFe(CN)6 solubility, Am residual concentration measured is lower that its concentration in the initial solutions. The solubility of EuFe(CN)6 was found to be equal to 30 mM. However, when precipitate formation occurs, the Eu residual concentration after phase separation is about in average 8 mM. When Am and Eu were simultaneously present at the same concentration in solution, the solubility of Am differs little from that measured with Am alone. For initial Am concentrations below 1 mM, the solubility of Am is higher than that observed in the absence of Eu. For initial concentrations of about 8 mM, the Am solubility is lower (about 0.7 mM) than that observed for Am alone. When the initial Eu concentration is constant at 29 mM, the Am precipitation efficiency is much higher than observed in the absence of Eu, for Am concentrations between 30 and 0.5 mM. The residual Am concentratixon in solution thus drops considerably in the presence of Eu (29 mM), and is about 0.04 mM for initial Am concentrations below 4 mM.

The primary patterns of isolation of actinides from their dioxides with supercritical carbon dioxide containing adducts of tri-n-butyl phosphate and other organic reagents with nitric acid has been investigated. The effective extraction of actinides from their dioxides was achieved using these adducts under common (ambient) conditions without supercritical carbon dioxide, which makes the performance of the process significantly easier. Extraction of uranium and the primary fission products from a simulated spent nuclear fuel has been studied. It was shown that at almost quantitative extraction of U (> 99%), most 95 Zr and 95 Nb (up to 90%) as well as 131 I, partially 103 Ru (∼ 30%), 99 Tc (20%) and lanthanides (up to 10%) also passed into the adduct phase. In this case complete separation of U from 137 Cs, 85 Sr, 140 Ba as well as from the bulk of 140 La, 141-144 Ce and 147 Nd was observed. After dissolution of the adduct containing U and partially fission products in liquid carbon dioxide the extract was transported into a separation column of a planetary centrifuge, and separation of U from remaining fission products was performed by countercurrent chromatography in the dynamic mode.