Solvent extraction of thorium (IV) and europium (III) ions by diphenyl-N,N-dimethylcarbamoylmethylphosphine oxide from aqueous nitrate media

The extractive properties of a CMPO-type extractant, diphenyl-N,N-dimethylcarbamoylmethylphosphine oxide (DPhiDMCMPO) in dichloromethane, have been investigated towards thorium (IV) and europium (III) ions in nitrate media at 20 degreesC. The conventional log-log plot analysis of the extraction equilibrium data reveals that the thorium and europium ions are extracted as complexes characterized by a metal/ligand ratio of 1:3 and 1:2, respectively. The effects of solvent, type and concentration of salting-out agent on the extraction abilities of the ligand were studied. The comparative extraction experiments in nitric acid medium showed that DPhiDMCMPO exhibits higher efficiencies than tri-n-octylphosphine oxide (TOPO). The influence of temperature on the extraction of the studied ions from 1 M sodium nitrate medium into 1,2-dichloroethane by DPhiDMCMPO was tested as a function of temperature in the range 20-40 degreesC. The distribution ratios of europium ions decrease when raising the temperature, while with thorium ions the opposite phenomenon was observed. From the distribution measurements, thermodynamic parameters such as the free energy (DeltaGdegrees), enthalpy (DeltaHdegrees) and entropy (DeltaSdegrees) changes associated with the extraction processes could be evaluated. (C) 2002 Elsevier Science B.V. All rights reserved.