Thermochemical features of biphasic transfer reactions of trivalent lanthanides and minor actinides (Am, Cm) have been measured using two-phase isothermal titration calorimetry and temperature dependent solvent extraction. The extraction measurements were made with tri-n-octylphosphine oxide (TOPO), a neutral solvating extractant and bis(2-ethylhexyl) phosphoric acid (HDEHP), a cation exchanger. Traditionally, thermodynamic parameters (ΔH, and ΔS) for biphasic reactions have been determined indirectly using the van’t Hoff method. However, calorimetric measurements of the enthalpy of metal ion transport across the liquid-liquid boundary can provide accurate results and simultaneously highlight important features of a given extraction system. The results in this presentation emphasize the calorimetric approach to determining the heats of extraction for the TOPO extractant system, illustrating the delicate thermodynamic balance between metal ion extraction and acid partitioning equilibria. Thermodynamic parameters describing minor actinide extraction by TOPO and HDEHP are presented and an energetic comparison of the two extraction systems is offered.

Studies on the thermodynamics of trivalent lanthanide/actinide extraction by tri-<i>n</i>-octylphosphine oxide and bis(2-ethylhexyl) phosphoric acid

249th National Meeting (2015)

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Studies on the thermodynamics of trivalent lanthanide/actinide extraction by tri-n-octylphosphine oxide and bis(2-ethylhexyl) phosphoric acid