The itinerant extraction behavior of f-elements and yttrium with octyl(phenyl)-N,N-diisobutylcarbamoyl-methylphosphine oxide

The extraction behaviour of selected trivalent lanthanides, actinides and yttrium was studied from thiocyanate and nitrate solutions using octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) in xylene as an extractant. It was found that these trivalent metal ions were extracted as MX(3).3CMPO (where X = SCN- or NO3-). The equilibrium constants(K) of the above species were determined by non-linear regression analysis. The K values of trivalent lanthanides in nitrate solutions do not increase monotonically with increasing atomic number(Z), but have a maximum at Eu. On the other hand, in thiocyanate solutions, the K values increase with increasing Z. In the extraction systems containing soft ligands like thiocyanate the distribution ratio (D) of Y is lower than that of La, whereas trivalent actinides Am and Cm have much higher D values than their corresponding counterparts in the lanthanide series, However, in the extraction systems containing a hard ligand such as nitrate, it is interesting to note that yttrium fits close to Tm which is the expected position based on its hydration energy and ionic radius. The reasons for these itinerant properties of yttrium, americium and curium have been discussed. The separation factors between these trivalent metal ions were calculated and compared with those obtained using the commercially important solvents like tributylphosphate (TBP), dihexyl-N,N-diethylcarbamoylmethylphosphonate (DHDECMP) and dibutylbutylphosphonate (DB[BP]), In the SCN--CMPO system high separation factor between Am and Eu has been obtained. The possibility of utilizing CMPO in the recovery of Y in a pure form from the mixtures containing Y, trivalent lanthanides and actinides has also been discussed.