Modeling Program Is Most Powerful Computational Tool Available for Unraveling Liquid-Liquid Extraction Data

The FORTRAN least-squares modeling program SXLSQI now represents the most advanced treatment of solvent-extraction equilibria available. From the earliest attempts to unravel the complexities of solvent-extraction distribution behavior, a major obstacle to progress has been the inability to unambiguously distinguish between effects due to species formation and effects due to nonideality. As a result, cumbersome and unrealistic experiments were required to produce understandable extraction data. Now, all that is changed. Because it is possible to automatically calculate effects of nonideality, experiments can be conducted under flexible conditions, including those which are typical of real processes. Data from such experiments can then be modeled with SXLSQI to determine the extraction complexes that have formed between extractants and extracted ions and molecules. Below is a typical model made possible by computations carried out with SXLSQI. In this model, a metal salt made up of M⁺ cations (purple spheres) and X^- anions (green spheres) is extracted by a crown ether to form various complexes in the organic phase, all related by a set of equilibria. In addition, one can learn the extent to which nonideality effects perturb the otherwise expected behavior. As a research tool, the program thus allows researchers to gain a deep understanding of a system and allows prediction of behavior over a wide range of conditions, even those that have not been tested. This understanding has in turn helped make it possible to develop both analytical and process applications of crown ethers. For example, an understanding of the model below allowed ORNL researchers to find suitable process conditions for cesium extraction from nuclear waste. To learn more about SXLSQI, check out the SXLSQI web page.