Synthesis of layered-type hydrous manganese oxides from monoclinic-type LiMnO2

Layered-type hydrous manganese oxides MnO2 . 0.70H(2)O and MnO2 . 0.22H(2)O with almost the same rod shape morphology as that of the precursor monoclinic-type LiMnO2 were synthesized. The structural transformations from monoclinic-type LiMnO2 to a birnessite-type MnO2 . 0.70H(2)O took place after lithium in LiMnO2 was extracted with 0.1 mol dm(-3) (NH4)(2)S2O8 solution without dissolution of manganese. The extraction of lithium from LiMnO2 with 0.5 mol dm(-3) HCl solution followed by the dissolution of manganese formed a trigonal-type MnO2 . 0.22H(2)O. The maximum ion exchange capacity of MnO2 . 0.22H(2)O toward alkali metal ions was found to be only 3 mmol/g; the material did not show any ion sieve properties. The pH titration study suggested that the MnO2 . 0.22H(2)O was a weak acidic adsorbent which was found to be a metastable phase. (C) 2001 Academic Press.