Synthetic inorganic ion exchange materials XLI: Ion exchange properties of cubic tantalic acid (HTaO3)

Cubic tantalic acid (C-TaA) was synthesized by Li+H+ ion exchange reaction with a 3 M (mol dm−3) sulfuric acid solution from LiTaO3. The LiTaO3 reactant was obtained by heating a mixture of Li2CO3 and Ta2O5 with molar ratio of 1:1 at 700, 800, and 900 °C. The X-ray diffraction pattern of C-TaA was indexed as cubic (space group Im3), with the lattice constant a0 = 7.75 – 7.62 Å. The C-TaA product showed an exchange reaction equivalent to one proton per one Li+ in a mixed solution of lithium nitrate and lithium hydroxide. The pH titration curves of C-TaA on the Li+H+ exchange system indicated a weak monobasic acid. C-TaA showed high uptake for lithium ions, whereas no appreciable amount of uptake was observed for other alkali metal ions in the range studied of pH 4–12. An extremely high selectivity was found for lithium ions, and the separation factor (a) of lithium ion to other alkali metal ions was higher than 103.