Spectroscopy, modeling and computation of metal chelate solubility in supercritical CO{sub 2}. 1998 annual progress report

Abstract

The overall objectives of this project are to gain a fundamental understanding of the solubility and stability of metal chelates in supercritical (SC) CO 2. Extraction with CO 2 is a excellent way to remove organic compounds from soils, sludges and aqueous solutions and recent research has demonstrated that together with chelating agents it is a viable way to remove metals, as well. We seek to gain fundamental knowledge that is vital to computing phase behavior, and modeling and designing processes using CO 2 to separate organics and metal compounds from DOE contaminated soils and mixed wastes. Our overall program is a comprehensive one to measure local solvation of metal chelates and to determine metal chelate stability in supercritical fluid (SCF) mixtures using UV-vis and FTIR spectroscopy. The spectroscopic studies provide information on the solution microstructure, which we are using in concert with our own and published solubility data to evaluate and develop thermodynamic models of the solubility behavior. Finally, we are implementing a more reliable computational technique, based on interval mathematics, to compute the phase equilibria using the thermodynamic models. This fundamental information about metal chelate stability and solubility in SC CO 2 is important in the design of processes using CO 2 to extract components from mixed wastes and in determining the optimum operating conditions. Research Progress and Implications This report summarizes work after 1 year and 8 months (9/15/96-5/14/98) of a 3 year project. Thus far, progress has been made in: 1) the measurement of the solubility of metal chelates in SC CO 2 with and without added cosolvents, 2) the spectroscopic determination of preferential solvation of metal chelates by cosolvents in SC CO 2 solutions, and 3) the development of a totally reliable computational technique for phase equilibrium computations.