METAL EXTRACTION BY ALKYL SUBSTITUTED DIPHOSPHONIC ACIDS - PART 4 - P,P'-DI(2-ETHYLHEXYL) BUTANEDIPHOSPHONIC ACID

As part of an ongoing investigation of the properties of dialkyl subst ituted diphosphonic acids as solvent extraction reagents for metal cat ions, we have studied the extraction of alkaline earth cations, Fe(III ) and representative actinides (Am(III), U(VI) and Th(IV)) at tracer-l evel concentration by o-xylene solutions of P,P'-di(2-ethylhexyl) buta nediphosphonic acid, H2DEH[BuDP]. The extractant and acid dependencies of these metal ions exhibited significant differences from those of t he previously investigated analogous extractants in which the two phos phonate groups are separated by a methylene or an ethylene bridge. The aggregation of H2DEH[BuDP] was investigated in toluene at 25 degrees C by vapor pressure osmometry. H2DEH[BuDP] was found to exist predomin antly as a trimeric species in the 0.1-0.005 molal concentration range . Osmometric measurements and infrared spectra indicate that Ca(II) is extracted into H2DEH[BuDP] solutions with little disruption of the st ructure of the extractant. Iron(IIE) causes significant deprotonation of the ligand and dramatically changes the apparent aggregation number . A comparison of the extraction of Ca(II), Am(III) and Fe(III) by H2D EH[BuDP] with data obtained using bis(2-ethylhexyl) phosphoric acid (H DEHP) or 2-ethylhexyl 2-ethylhexylphosphonic acid (HEH[EHP]) as the ex tractant indicates that H2DEH[BuDP] has characteristics similar to the se monofunctional analogs. Infrared spectra of the Ca(II) and Fe(III) salts of H2DEH[BuDP] show a shift of both V-asym(POO-) and v(sym)(POO- ) to lower frequencies relative to their values in the sodium salt. Th is indicates a symmetrical interaction between the metal ion and the p hosphonate groups through chelate and/or bridging interactions.