Extraction of Cesium by a Calix[4]arene‐Crown‐6 Ether Bearing a Pendant Amine Group

Abstract

The goal of this work was to evaluate the role of the amino group of 5‐aminomethylcalix[4]arene‐[bis‐4‐(2‐ethylhexyl)benzo‐crown‐6] (AMBEHB) in the extraction of cesium from acidic and basic mixtures of sodium nitrate and other concentrated salts. The extraction of cesium from nitrate media was measured as a function of extractant concentration, nitrate concentration, cesium concentration, and pH over the range 1–13. The initial studies showed a moderate decrease in the extraction of cesium in acidic media, which indicated the binding of cesium by the calixarene‐crown was weakened by the protonation of the amine group. The results also indicated that a 1∶1∶1 Cs‐ligand‐nitrate complex is formed in the organic phase. To further evaluate AMBEHB, the empirical data were mathematically modeled to determine the formation constants of the complexes formed in the organic phase. The resulting formation constants showed that the attachment of the amine group to the calixarene‐crown molecule reduced the binding stability for the cesium ion upon contact with an acidic solution. This supports the hypothesis of charge repulsion as the basis for more efficient stripping of cesium via pH‐switching.

Keywords:

• 5‐Aminomethylcalix[4]arene‐[bis‐4‐(2‐ethylhexyl)benzo‐crown‐6]
• cesium
• solvent extraction
• formation constants
• pH‐switching

Acknowledgements

This research was partially sponsored by the Environmental Management Science Program of the Offices of Science and Environmental Management, U.S. Department of Energy, under contract number DE‐AC05‐00OR22725 with Oak Ridge National Laboratory, managed by UT‐Battelle, LLC. One of us (BH) wishes to thank the College of Arts and Sciences, Tennessee Technological University for travel funds and Sigma Xi for a grant‐in‐aid of research.