Quantification of enthalpy of extraction of Eu(III)-glycolamide solvent systems using isothermal solution calorimetry-Influence of extraction parameters and solvent aggregation

Abstract

The present work highlights the utility of isothermal solution calorimetry as a reliable and convenient tool for the determination of enthalpy of extraction (ΔHextr) of metal ions under biphasic solvent extraction conditions. In comparison to the conventional indirect method based on Van't Hoff isotherm analysis, calorimetric method offers the flexibility of direct enthalpy measurements under a variety of operating conditions. The ΔHextr of Eu(III) at different HNO3 concentrations was measured for N,N,N’,N’-tetraoctyldiglycolamide (TODGA) and N,N-di-octyl-2-hydroxyacetamide (DOHyA) solvents for the first time using this method. A strong dependence of ΔHextr with changes in aqueous phase acidity as well as the concentration of solvent phase was discerned during the measurements. Parallel measurements using DLS spectroscopy divulged that the observed decrease in ΔHextr is a consequence of the aggregation of extractants. The pivotal role of aggregation of solvents on the extraction enthalpy of solvent extraction systems was demonstrated by a comparison of the results in two solvent systems with different aggregation properties.