Monday, June 18, 2007 - 11:35 AM
The Peregrins (Boise Centre on the Grove)

Development of a Two-phase Calorimetric Method for the Studies of Thermodynamics of Solvent Extraction

Peter Zalupski and Ken Nash. Washington State University, Pullman, WA

Solvent extraction chemistry plays a fundamental role in the proposed chemical treatment of nuclear waste prior to disposal. The development of efficient separation schemes based on liquid-liquid metal distributions has relied heavily on studies of thermochemistry of metal extraction. Calorimetric measurements offer an opportunity for a careful determination of heats of extraction; however, the inherent complexity of a two-phase system has been an obstacle to the application of conventional calorimetry to solvent extraction systems. Efficient phase contact without excessive generation of heat proved troublesome, making the van't Hoff analysis (temperature dependence of extraction coefficient) a method of choice for most thermodynamic studies of such systems. In this report, a method for calorimetric investigation of the heats of metal distribution in a two-phase system will be presented. The extraction of lanthanide metal ions from nitrate media by bis(2-ethylhexyl) phosphoric acid (HDEHP) was chosen as a model example to develop the two-phase calorimetric method. The enthalpy of extraction of europium(III), derived from its quantitative transfer to the organic phase, was compared with that obtained from the temperature dependence of the extraction constant. The process of the collection of thermodynamic parameters for the extraction of the complete lanthanide series by HDEHP, as well as the applicable correction factors, will be discussed with emphasis on utilizing this method for routine analyses of thermochemistry of liquid-liquid distribution systems.