Layer Structured Manganese Oxide Hydroxides

VI: Recrystallization of Synthetic Buserite and the Influence of Amorphous Silica and Ferric Hydroxide on its Nucleation

Abstract

Crystallinity and morphology of synthetic 10 Å-manganate (buserite) depend a) on the presence or absence of amorphous colloidal silica and co-precipitating amorphous ferric hydroxide, and b) on the ageing under pressure or normal conditions. Experiments have been carried out to age 10 Å-manganate at room temperature up to 14 years and to autoclave Ca-, Cu-, and Mg- buserite up to 200 hours at temperatures from 20 to 100 °C. Co-precipitation experiments have been carried out with amorphous silica and ferric hydroxide. Recrystallization leads to an ordering of the structure visible in additional reflections in the electron diffraction and to a crystal growth in one or, in twinned crystals, in two preferred directions. The presence of amorphous silica can entirely suppress 10Å-manganate nucleation, and z-disordered manganate precipitates. Co-precipitating ferric hydroxide also suppresses 10Å-manganate nucleation, while previously prepared ferric hydroxide has no influence. This explains the layered texture of deep-sea manganese nodules as an oscillating reaction controlled by depletion and enrichment of the aquatic phase in silica and ferric hydroxide.