SYNTHETIC INORGANIC ION EXCHANGE MATERIALS XLlV: SYNTHESIS AND ION EXCHANGE PROPERTIES OF CUBIC NIOBIC ACID (HNbO_3)

摘要

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 LiNbO_3. The LiNbO_3, was obtained by heating a mixture of Li_2CO_3 and Nb_2O_5 with molar ratio of l:l at 900deg.C for 24 h. X-ray diffraction pattern of C-NbA was indexed to a cubic structure (space group Im_3), with the lattice constant ao = 7.6445 A (A = 100 pm). The C-NbA product showed an exchange reaction equiv- alent 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-l2. An extremely high selectivity was found for lithium ions, and the separation factor (a) of lithium ions to other alkali metal ions was higher than l0~3.