The extraction of americium and strontium by PP'-Di(2-ethylhexyl) benzene-1,2-diphosphonic acid

A new acidic organophosphorus extractant, P,P'-di(2-ethylhexyl) benzene-1,2-diphosphonic acid (H2DEH[1,2-BzDP]), has been synthesized. Though the extractant proved unstable with respect to acid hydrolysis upon storage at room temperature, it was sufficiently stable in o-xylene solution under refrigeration to determine its aggregation and extraction properties for Sr2+ and Am3+ between 25 and 60degreesC. Slope analysis of radioanalytical data and the results of osmometric measurements indicate that the dominant extraction reaction for both metal ions is Mn+ + n HL reversible arrow MLn + n H+ where n = 2 for Sr(II) and 3 for Am(III). In the Sr system there is also evidence for the extraction of SrNO3+. As the extractant aggregation and extraction stoichiometries do not change significantly with temperature, it was possible to derive enthalpies and entropies of extraction from the temperature dependence of the metal extraction equilibrium constants between 25.0 and 60.0degreesC. The extraction of both metal ions is driven by an exothermic enthalpy and opposed by unfavorable entropies. The thermodynamic data are discussed in comparison with earlier data on the thermodynamics of extraction of these metal ions by analogous ligands containing aliphatic alkyl linkages between the functional groups and other data from the literature.