A short review is given on our current anion-exchange studies of element 104, rutherfordium (Rf), in HCl and HNO3 solutions. The distribution coefficients of the Rf homologues Zr, Hf, and Th (IV), and Pu (IV) on an anion-exchange resin were measured in 1.0-11.5 M HCl and 1.1-13.1 M HNO3 with a batch method using the radiotracers 88Zr, 175Hf, 234Th, and 237Pu. In experiments for the short-lived 261Rf, the isotopes 85Zr, 169Hf, and 169Rf were produced in the 18O-induced reactions on natGe, 248Gd, and 248Cm targets, respectively, and their anion-exchange behavior in 4.0-11.5 M HCl and 8.0 M HNO3 was investigated using the Automated Ion-exchange separation apparatus coupled with the Detection system for Alpha spectroscopy (AIDA). In the HCl system, the percent adsorption of Rf on the anion-exchange resin increases steeply with increasing HCl concentration from 7.0 M to 11.5 M. This adsorption behavior is similar to that of the group-4 elements Zr and Hf, and is quite different from that of the pseudo-homologue Th (IV). The percent adsorption decreases in the order Rf>Zr>Hf. In the HNO3 system, Rf behaves like Zr and Hf in 8.0 M HNO3 but not like Pu (IV) and Th (IV), implying the formation of cationic or neutral species.
