Accurate characterization of liquid-liquid distribution equilibria often relies on proper consideration of non-ideal solution chemistry in aqueous electrolyte and non-aqueous solute mixtures. Quantitative description of chemical interactions in complex liquid phases may be realized through the process of thermodynamic parameterization of theoretically represented mixtures. The construction of such thermodynamic models allows for numerical representation of non-ideal solute behavior in aqueous and organic phase components of a liquid-liquid distribution. Here we describe a process of building such thermodynamic model for aqueous buffer: Eu3+ / H+ / Na+ / NO3- / H2Mal / HMal- / H2O, where Mal describes malonate, based on Pitzer ion-interaction theory. Predictive description of the equilibrium set guiding the liquid-liquid distribution of Eu(III) between aqueous malonate solutions and mixtures of bis(2-ethylhexyl)phosphoric acid, HDEHP, in n-dodecane, as afforded by a computational package SXFIT, will be illustrated. The program is an iterative fitting procedure, which allows the identification of an equilibrium model for the distribution of a solute in a liquid-liquid system. We will discuss the alterations to SXFIT calculations based on continuous improvements in the accuracy of the thermodynamic model for aqueous malonate mixtures.

Building thermodynamic models of solution mixtures to support predictive modeling of liquid-liquid distribution systems

244th National Meeting (2012)

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