Insights Into f-element Coordination Chemistry in TALSPEAK Systems

Thermodynamic data from the literature properly predict lanthanide–actinide separation factors in the TALSPEAK process, but fail to predict the observed steep acid dependence that is seen when the pH is raised above 3. In this work, features of lanthanide coordination chemistry and solute partitioning in TALSPEAK are examined to improve understanding of the fundamental chemistry that controls this process and to explain this anomaly. To accomplish this, a variety of spectroscopic techniques have been applied to the task. In addition, since the issue with TALSPEAK appears to lie in part in the definition of thermodynamic equilibria, complementary studies have been conducted elucidating fresh estimates of selected thermodynamic parameters of relevance to this system. To extend the utility of this investigation, some of these studies have examined the properties of substitute reagents within the general framework of TALSPEAK and TALSPEAK-like systems. In this report, observations from NMR, ESI-MS, and optical spectroscopic studies of lanthanide complexes are combined with thermodynamic modeling to provide fresh insights into lanthanide-actinide separations systems based on aqueous complexing agents.