Aggregation of complexes formed in the extraction of selected metal cations by P,P'-di(2-ethylhexyl methanediphosphonic acid

The aggregation of several metal complexes formed during solvent extraction with P,P'-di(2-ethylhexyl) methanediphosphonic acid, H2DEH[MDP], in deuter ated toluene, has been investigated by small angle neutron scattering (SANS ). The SANS results show that the Ca(II)-, AI(III)-, La(III)- and Nd(IU)-H2 DEH[MDP] compounds exhibit little or no tendency to aggregate. Uranyl compl exes of H2DEH[MDP] at high metal loading form small aggregates with an aggr egation number of approximately 14. This behavior is in sharp contrast with the Th(IV)-H2DEH[MDP] system which forms large aggregates in the organic p hase under high metal loading conditions. The aggregation behavior of the v arious metal-H2DEH[MDP] compounds is discussed in light of the information obtained from earlier solvent extraction, vapor pressure osmometry, and inf rared spectroscopy studies.