Cesium-137 Extraction from Nitric Acid Media with Calix[4]arene-Crown-6 Ether Solutions in Bis(tetrafluoropropyl) Carbonate

The physicochemical and extraction properties of calixarene crown ethers: 1,3-alt-bis(octyloxy)calix[4]arene-crown-6 (II) and its derivatives with α-phenylene (I), methylenepropoxy (IV) and methylene(2,2,3,3-tetrafluoropropoxy) (III) substituents in the crown ether ring, were studied. Solutions of compound II in bis(2,2,3,3-tetrafluoropropyl) carbonate (BK-1) effectively extract cesium from 3 mol/L nitric acid already at a concentration of 0.001 mol/L. The introduction of substituents into the crown ether ring significantly reduces the efficiency of cesium extraction, but increases the solubility of calixarene crown ethers in bis(2,2,3,3-tetrafluoropropyl) carbonate. The data on the solubility of calixarene crown ethers in water and 3 mol/L nitric acid, the distribution between the organic and aqueous phases, and the rate of interaction with nitric acid were obtained. Calixarene crown ether I with an α-phenylene substituent reacts with 3 mol/L nitric acid approximately 2 times faster than dibenzo-21-crown-7. The other calixarene crown ethers studied do not react with nitric acid under the similar conditions. Quantum chemical modeling, including optimization of the structure geometry and calculation of vibrational frequencies, was performed for the molecules of calixarene crown ethers, DB21C7 and their complexes with the cesium cation. The calculated ΔG values for the complexation of ligands with the cesium cation correlate well with the experimental lgD (except for compound III with a fluorinated substituent). Solutions of calixarene crown ethers in bis(2,2,3,3-tetrafluoropropyl) carbonate exhibit selectivity for cesium and do not extract Eu and Am from nitric acid media.