INVESTIGATION OF AGGREGATION IN SOLVENT-EXTRACTION OF LANTHANIDES BY ACIDIC EXTRACTANTS (ORGANOPHOSPHORUS AND NAPHTHENIC ACID)

Three acidic extractants (I) di(2-ethylhexyl) phosphoric acid (HDEHP), (II) 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (HEHPEHE) a nd (III) naphthenic acid were employed in preparing the samples for th e characterization of the coordination structure of lanthanide-extract ant complexes and the physicochemical nature of aggregates formed in t he organic diluent of the solvent extraction systems. Photo correlatio n spectroscopy (PCS) results on the aggregates formed by the partially saponified HDEHP in n-heptane showed that the hydrodynamic radius of the aggregates was comparable to the molecular dimensions of HDEHP. Th e addition of 2-octanol into the diluent, by which the mixed solvent w as formed, increased the dimensions of the corresponding aggregates. A ggregates formed from the lanthanide ions and HDEHP in the organic pha se of the extraction systems were found very unstable. In the case of naphthenic acid, PCS data showed the formation of w/o microemulsion fr om the saponified naphthenic acid in the mixed solvent. The extraction of lanthanides by the saponified naphthenic acid in the mixed solvent under the given experimental conditions was a process of destruction of the w/o microemulsion. A possible mechanism of the breakdown of the w/o microemulsion droplets is discussed.