Extraction of Np(IV), Np(VI), Pu(IV) and U(VI) with amides, BEHSO and CMPO from nitric acid medium

The extraction of Np(IV), Np(VI), Pu(IV) and U(VI) from a nitric acid medium has been carried out with dibutyldecanamide (DBDA), dihexyldecanamide (DHDA), bis-2-ethylhexylsulphoxide (BEHSO) and octyl(phenyl)-N-N-diisobutyl-carbamolymethylphosphine oxide (CMPO) using n-dodecane as the diluent. The order of extraction for the metal ions is CMPO>BEHSO>DHDA>DBDA. The species extracted into the organic phase was found to be the disolvate with all the extractants while using hexavalent metal ions Np(VI) and U(VI) and also with tetravalent ions Np(IV) and Pu(IV) in the case of BEHSO and CMPO. However, in the case of DBDA and DHDA, Np(IV) and Pu(IV) were extracted as the trisolvate species. The equilibrium constant (K) for the formation of the above species has been evaluated after applying the possible correction factors. In general, logK increases with increasing basicity of the extractants. In the case of amides, the plot of logK verses kH (acid uptake equilibrium constant) gave straight lines which could be represented by the empirical equation: logKU(VI)=5.17 kH+0.18 and logKPu(IV)=3.11 kH+1.81 for the respective metal ions. With the help of these empirical equations it is possible to predict the equilibrium constant values of amide complexes of U(VI) or Pu(IV) if the kH values of amides are known. The solid complexes of U(VI) with DHDA and CMPO were synthesized and characterized by elemental analysis and IR spectra. Two molecules of DHDA and only one molecule of CMPO are bound with U(VI). The bidentate nature of CMPO in its solid species has been confirmed. (orig.)