The influence of anions on the distribution coefficients of hard acid-metals for anion-exchange resin in HF-H3BO3 media

The distribution coefficients, Ksub(d), of eighteen hard acid-metal ions for a strongly basic anion-exchange resin were determined in HF-H3BO3 media in the presence of Cl- or NO3-, SO42-, and ClO4-, and the relation between the adsorbabilities of the coexisting anions and the Ksub(d) values of the metal ions was discussed. The fluoride-ion concentration is quite-low in HF-H3BO3 media because of the complex formation of the fluoride ion with boric acid, and most of the hard acid-metal ions have lower Ksub(d) values in HF-H3BO3 media than those in a hydrofluoric acid solution. By varying the kinds of coexisting anions and their concentrations in HF-H3BO3 media containing less than 0.02M(1M=1 mol dm-3) of fluoroborate ions, the Ksub(d) values of metal ions can be controlled to allow the anion-exchange separations. As fluoroborate ions, e.g., BF4- or BF3OH-, are strongly adsorbed on the resin, metal ions which are strongly held on the resin can be eluted by media including fluoroborate ions in higher concentrations. By using HF-H3BO3 media and selecting the coexisting anions, an effective mutual separation of titanium-zirconium, titanium-uranium, tin-niobium, and molybdenum-tungsten can be attined. (author)