On-line anion exchange of rutherfordium in HF/HNO₃ and HF solutions

Summary

The fluoride complexation of the group-4 elements Zr, Hf, and Rf, and of the pseudo-homolog Th, was previously investigated in mixed HNO₃/HF solutions by studying K_d values on both cation-exchange resins (CIX) and anion-exchange resins (AIX) using the automated rapid chemistry apparatus ARCA. On the CIX, the fluoride complexation of Rf was found to be weaker than that of Zr and Hf but stronger than that of Th. On the AIX, the competition for the binding sites by the counter ion NO₃^- was found to be stronger for the fluoride complexes of Rf than for those of Zr and Hf. The aim of the present work is to add independent evidence to the latter result by measuring K_d values for Rf on the AIX in 0.1 M HNO₃/0.5 M HF and in 0.01 M HF without any HNO₃. The results are obtained via an activity ratio of the long-lived α-decay descendant of ^261mRf, 20-d ²⁵³Es, using the multi-column technique (MCT). These experiments corroborate the seemingly much more pronounced competition of NO₃^- for the exchanging sites of the AIX with respect to [RfF_x]^(x-4)- than with [ZrF_x]^(x-4)- and [HfF_x]^(x-4)-.