Periodic Patterns in Selectively Separating Actinide–Lanthanide Ion Pairs by Triamide Extractants

Lanthanide/actinide (Ln/An) separation is a critical step in the reprocessing of spent nuclear fuels, enabling a more efficient utilization of nuclear resources and reducing nuclear waste contamination. However, separating Ln/An ions remains a significant challenge due to the similarity in their physicochemical properties. The periodic table and periodic law offer powerful tools for guiding chemical research. As Ln/An nuclides fall within the periodic trends, this provides possibilities for the optimized design of selective extractants. In this study, we systematically investigated the periodic patterns through which nitrilotriacetamide (NTAamide) selectively separates actinide-lanthanide ion pairs. The results indicate that separating ion pairs within the same group follows the <i>Difference Model</i>, while separating ion pairs of the same period follows the <i>Similarity Model</i>. Furthermore, our modified extractants exhibited enhanced separation selectivity for Ln/An ion pairs from the same group or period, which was validated by retrosynthetic analysis based on machine learning models. Detailed computational characterizations reveal that the modulation of the metal-oxygen bond strength is the microscopic origin underlying the enhanced separation performance.