[en] Various aspects of the synergistic extraction and separation of actinides and lanthanides from mixed aqueous-organic solutions (polar media) have been reviewed. Notable recent developments as well as its current status in solvent extraction systems where the aqueous acidic phase contains an organic solvent which is completely miscible with water, are presented briefly. In general, extraction increases in the presence of an organic component. The less polar the additive, the higher is the tendency to form neutral metal complexes which ultimately brings about an increase in the extraction. In a polar media, synergism has mostly been observed, though antagonism is not uncommon. An attempt has been made to classify the factors that play an important role in polar phase extractions. Also, their influence particularly on the extractability of actinides and lanthanides is discussed. The discussion is limited to the factors affecting the extraction equilibria, effect of dielectric constant of the polar medium, solvation of the extracting agent and to the composition and stability of the metal complex in the organic phase. Hydroxyl (OHsup(-)) bearing organic additives, e.g. alcohols, and solvents not containing the hydroxyl group such as acetone, dimethylsulphoxide, tetrahydrofuran, amides and acetonitrile etc. are the two major classes of organic additives considered in these studies. Generally, synergistic effect in extraction of the ion-association (TBP, TOPO, sulphoxides etc.) or anion exchange (amines etc.) type is relatively more pronounced compared to other extractions. A tabular summary concerning extraction of actinides and lanthanides from polar media is appended for ready reference. (author)

[en] A novel type of extractant for actinides called bis(dioctylcarbamoylmethyl) sulfoxide is described which neither contains phosphorus nor entails the addition of tributyl phosphate as phase modifier for extraction. This extractant, abbreviated as CMSO, has been found to be freely soluble in dodecane and to form no third phase even with concentrations of nitric acid as high as 10M. The distribution ratios for the extraction of Am(III), Pu(IV) and U(VI) at trace levels have been found to be 13, 220 ad 11, respectively, from 5M nitric acid using 0.2M CMSO in dodecane and those for backextraction have been found to be 2 x 10^-4, 8 x 10^-3 and 5 x 10^-2 using 0.01M nitric acid, 0.1M oxalic acid and 0.35M sodium carbonate, respectively. Similar distribution ratios were obtained with the recycled extractant. Extraction was found to be very rapid. Eu(III) and Sr(II) were found to be moderately extracted with distribution ratios of 2 and 0.77, respectively, while the extraction of Cs(I) was negligible (K_D 0.005). (author) 11 refs.; 1 fig.; 1 tab

[en] Merits of using sulfoxides as extractants in the purex process are discussed. (author)

[en] Extraction behavior of plutonium(IV), uranium(VI), and some fission products from aqueous nitric acid media with di-n-octylsulfoxide (DOSO) has been studied over a wide range of conditions. Both the actinides are extracted essentially completely, whereas fission product contaminants like Zr, Ru, Ce, Eu, and Sr shown negligible extraction. The absorption spectra of sulfoxide extracts containing either Pu⁴⁺ or UO₂²⁺ indicate the species extracted from nitric acid into the organic phase to be Pu(NO₃)₄ . 2DOSO and UO₂(NO₃)₂ . 2DOSO, respectively. Extraction of these actinides decreases with increasing temperature, indicating the extraction to be exothermic. DOSO extracts plutonium and uranium better than di-n-hexylsulfoxide (DHSO) under all conditions and is also more soluble in aromatic diluents than the latter. The effect of gamma radiation on the extraction properties of DOSO is found to be similar to that of DHSO. 6 figures, 5 tables

[en] The results of the determination of combined carbon and free carbon in uranium carbide in oxygen by a differential temperature technique suggest the premature oxidation of the free carbon due to the local heating of the sample caused by the exothermic decomposition of the carbide. However, it was found possible to overcome this difficulty employing air as supporting gas at controlled heating rates. (orig.)

[en] Synergistic extraction of uranyl ion with 1-phenyl-3-methyl-4-benzoyl pyrazolone-5 (HPMBP) and aliphatic sulfoxides of varying basicities, viz di-isoamyl (DIASO), di-n-hexyl (DHSO), di-n-septyl (DSSO), di-n-octyl (DOSO), di-n-nonyl (DNSO), di-n-decyl (DDSO) or di-n-undecyl (DuDSO) sulfoxide was studied at 30+-0.1 deg C. The organic phase equilibrium constant (log Ks) was found to increase with the basicity of the sulfoxide up to DOSO beyond which there is a gradual decreasing trend which has been attributed to the effect of possible steric hindrance (spatial) involved in the bonding of the higher sulfoxides (greater than 8 carbon atoms) with UO₂(PMBP)₂ chelate. The entropy values for sulfoxides with eight or more carbon atoms are much more negative as compared to the lower sulfoxides. (author)

[en] Extraction behaviour of plutonium(IV) from nitric acid media by two long-chain aliphatic sulphoxides, namely, di-hexylsulphoxide and di-n-octylsulphoxide has been investigated in the presence of several water-miscible organic solvents to study their possible synergistic effect on metal ion extraction. Methanol, ethanol, n - and isopropanol, dioxane, acetone as well as acetonitrile were used as the organic components of the mixed (polar) phase. These additives affected the extraction to varying degrees. Thus, extractability of Pu increases 2-3 fold with increasing concentration (upto 20%) of acetonitrile, acetone, methanol and ethanol while it decreases with increasing concentration of n- and isopropanol. At high concentration of the former, the synergism changes into antagonism. Possible reasons for such behaviour are briefly discussed. Among these organic additives, maximum enhancement in the extraction of Pu(IV) was observed in the presence of acetonitrile. The relative increase in extraction was found to be more at lower sulphoxide concentrations. (author)

No abstract available

[en] The extraction behaviour of plutonium (IV) from nitric acid media by two long-chain aliphatic sulfoxides, namely, di-n-hexylsulfoxide and di-n-octylsulfoxide has been investigated in the presence of several water-miscible organic solvents to study their possible synergistic effect on metal ion extraction. Methanol, ethanol, n- and iso-proparnol, dioxane, acetone as well as acetonitrile were used as the organic component of the mixed (polar) phase. These additives affected the extraction to varying degrees. Thus the extractability of Pu increases 2-3 fold with increasing concentration (up to 20%) of acetonitrile, acetone, methanol and ethanol while it decreases with increasing concentration of n- and iso-propanol. At high concentration of the former, synergism changes into antagonism. Possible reasons for such behaviour are briefly discussed. Among these organic additives, the maximum enhancement in the extraction of Pu(IV) was observed in the presence of acetonitrile. The relative increase in extraction was found to be more at lower sulfoxide concentrations. (author)

[en] The oxidation of plutonium(IV) to plutonium(VI) with sodium bismuthate was investigated in dilute nitric acid media. Essentially quantitative oxidation of tracer as well as macro (mg/ml) concentration of plutonium could be achieved on using a slight excess of the oxidant in the acid range of 0.01-2M HNO₃. Plutonium(VI) thus prepared was found to be stable for a few days in solutions free from undissolved sodium bismuthate. The effects of variables on oxidation reaction are discussed briefly. The extent of oxidation was checked by an absorptiometric method. (author)