Synthetic inorganic ion exchange materials XLIV: synthesis and ion exchange properties of cubic niobic acid (HNbO3)

A cubic niobic acid (C-NbA) was synthesized by Li+/H+ ion exchange reaction with an 8 M (mol dm−3) nitric acid solution from LiNbO3. The LiNbO3 was obtained by heating a mixture of Li2CO3 and Nb2O5 with molar ratio of 1:1 at 900°C for 24 h. X-ray diffraction pattern of C-NbA was indexed to a cubic structure (space group Im3), with the lattice constant a0 = 7.6445 Å (Å = 100 pm). The C-NbA 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-NbA on the Li+/H+ exchange system indicated a weak monobasic acid. C-NbA showed high uptake for lithium ions, whereas no appreciable amount of uptake was observed for other alkali metal ions in the pH range 4–12. An extremely high selectivity was found for lithium ions, and the separation factor (α) of lithium ions to other alkali metal ions was higher than 103.