Extraction of Am, Eu, Tc, and Pd from nitric acid solutions with phosphorylated calixarenes

Abstract

Extraction of Am, Eu, Pd, and Tc from 0.1–3.0 M HNO3 with solutions of phosphorylated calix[n]arenes in m-nitrobenzotrifluoride (NBTF) was studied. The ring size and position of phosphoryl groups (in the upper or lower rim) affect the extraction of Am and Eu significantly and that of Tc and Pd only slightly. Calix[4]arenes phosphorylated at the upper rim extract Am and Eu considerably better than do their analogs with substituents in the lower rim and substituted calix[6]arenes. Compounds with the phosphoryl group linked to the calixarene core by the methylene bridge show the highest extracting performance. In contrast to monodentate phosphine oxides, in calix[4]arenes the size of the alkyl substituent at the P atom strongly affects the efficiency of extraction of the radionuclides. With a decrease in the length of the alkyl radical in substituents −CH2P(O)Alk2, the distribution ratios of all the radionuclies, as a rule, decrease. With a decrease of Alk in −CH2P(O)PhAlk, the distribution ratios increase for Eu and Am but remain unchanged for Tc and Pd. Calix-arenebis(methylenediphosphonates) with the propoxy substituents at the P atom extract Eu and Am hundreds times more efficiently than do their analogs with methoxy, isopropoxy, and butoxy substituents. The possibility of joint recovery of Am, Eu, Tc, and Pd from nitric acid solutions with calix[4]arenes containing dialkylmethylenephosphine oxide substituents in the upper rim was demonstrated. The prevalent species formed in the extraction of Tc are complexes of the composition M2L. The composition of complexes formed by calix-arenes with Am and Eu depends on the preparation procedure.