METAL-ION EXTRACTION/INSERTION REACTIONS WITH TODOROKITE-TYPE MANGANESE OXIDE IN THE AQUEOUS-PHASE

Todorokite-type magnesium manganese oxide (ToMO(Mg)) was prepared by hydrothermal treatment of Mg2+-exchanged buserite-type manganese oxide. The extraction/insertion reactions of the metal ions with the manganese oxide were investigated by chemical and X-ray analyses, FT-IR spectroscopy, pH titration, and K-d measurements. Mg2+ and Mn2+ ions in the (3 x 3) tunnel sites of the manganese oxide were topotactically extracted by acid treatment. Alkali metal ions could be inserted into the (3 x 3) tunnel sites of the acid-treated sample (ToMO(H)). The extraction reaction proceeded by redox-type and ion-exchange-type mechanism, and most of the insertion reaction by ion-exchange-type mechanism. In the pH titration studies, the acid-treated sample showed dibasic acid behavior toward Li+, Na+, and K+ but monobasic acid behavior toward Cs+ and (CH3N+. The affinity order was (CH3-N+ < Cs+ = Li+ < Na+ < K+ at pH 5 and (CH3N+ < Cs+ < K+ < Na+ < Li+ at pH 10. The distribution coefficient (K-d) Of the metal ions increased with an increase in the effective ionic radius. The effective pore radius of ToMO(H) was evaluated as about 2.7 Angstrom from the structural parameters of the (3 x 3) tunnel.