Fluoride complexation of rutherfordium (Rf, element 104)

The fluoride complexation of the group-4 elements Zr, Hf and Rf, and of the pseudo-homolog Th, has been investigated in mixed HNO3/HF solutions by stu dying K-d values on both cation exchange resins (CIX) and anion exchange re sins (AIX) using the automated rapid chemistry apparatus ARCA. On the CIX, the four elements are strongly retained as cations below 10(-3) M HE For Zr and Hf. the decrease of the K-d values due to the formation of fluoride co mplexes occurs between 10(-3) hi HF and 10(-2) M HF. For Rf and Th, this de crease is observed at one order of magnitude higher HF concentrations. On t he AIX, for Zr and Hf, a rise of the K-d values due to the formation of ani onic fluoride complexes is observed between 10(-3) M HF and 10(-2) M HF, i. e. in the same range of HF concentrations where the decrease of the K-d val ues on the CDC is observed, yielding a consistent picture. For Rf and Th, o n the AIX, no rise of the K-d values is observed even if the HF concentrati on is increased up to 1 M. By varying the concentration of the counter ion NO3- which is competing for the binding sites on the AIX resin, it could be shown, nevertheless, that Rf does form anionic fluoride complexes. Apparen tly, there is a more specific competition of NO3- with respect to [RfF(x)]( (x-4)-) than with [ZrFy]((y-4)-) and [HfFz]((z-4)-).