THERMODYNAMICS OF EXTRACTION OF Am(III) AND Eu(III) FROM NITRATE AND THIOCYANATE MEDIA WITH OCTYL(PHENYL)-N,N-DIISOBUTYLCARBAMOYLMETHYLPHOSPHINE OXIDE

The extraction of Am(III) and Eu(III) from 1.0 M NH4NO3 and NHS4SCN at pH 2.60 into octyl(pheriyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) in n-dodecane has been studied in the temperature range 15.0 to 45.0°C. Under all conditions, the species ML3·CMPO is the dominant extracted complex. The extraction equilibrium constants are at least 103 higher in the SCN- systems than in the NO3 - systems. This difference is attributed to the relative energy associated with transfer of the anions from the aqueous to the: extractant phase. Extraction enthalpies and entropies have been calculated in each system from the temperature dependence of Kex. Enthalpies are considerably more exothermic in the thiocyanate system for both metal ions. Comparison of ΔHAm SCN with ΔHEU SCN gives a possible indication of enhanced Am-SCN bond strength in the extracted complex.