(514d) Chemical Activities and Non-Ideal Behavior for Organic Solvents In Treatment of Used Nuclear Fuel

Solvent extraction using Di(2-ethylhexyl) phosphoric acid (HDEHP, D2EHPA) is an effective separation technique for  the purification of various metals, including the extraction and/or partitioning of various metal ions in used nuclear fuel. Successful separation of particularly useful or harmful elements from nuclear material could minimize the volume of nuclear waste requiring long term storage. Accurately modeling the process for industrial use requires a thorough understanding of the solution chemistry of the system. However, the majority of research characterizing the behavior of HDEHP relies on extraction data, rather than data from a binary HDEHP/solvent system. An improved understanding of HDEHP in the simpler, more fundamental system will either elucidate effects that the extraction studies overlook or independently support their results. With this motivation, we present and discuss the results of our study examining the role of temperature and concentration on the non-ideal behavior of the binary HDEHP and n-dodecane system based on data from vapor pressure osmometry. Activity coefficients for both components in the binary system have been found using a first approximation based on regular solution theory. Results show that although the fit of the model is reasonably accurate and activity coefficients can be found the regular solution theory cannot account for negative deviations in the activity coefficients from ideality, i.e. activity coefficients are always above unity. This behavior may introduce erroneous behavior for dilute solutions and more advanced and possibly accurate models have been investigated and will be presented.