Transformation of the phyllomanganate vernadite to tectomanganates with small tunnel sizes: Favorable geochemical conditions and fate of associated Co

The present work uncovers the geochemical control on nature (tunnel size) of tectomanganates formed from layered precursors, and thus provides insights into formation Mn oxides in natural environments. Large tunnel sizes are favored under circum-neutral conditions, whereas low pH conditions favor with smaller sizes. Both increased proportions Mn(III) vernadite/birnessite layers resulting subsequent enhancement disproportionation during transformation contribute to fate foreign elements phyllomanganate-to-tectomanganate mineral is another important aspect this transformation, together impact these transformation. Layered have indeed a pivotal influence cycling transition metals, including Co, that possess strong affinity for species. experimental shows todorokite (3 × 3 size), hollandite (2 2), or nsutite (intergrown 1 2 fragments) essentially unaffected by limited Co-enrichment (?5 at.%) initial phyllomanganate structure. Higher Co contents reduce content Jahn-Teller distorted octahedra precursor hamper phyllomanaganate-to-tectomanganate Finally, retained structure their part (?20%) precursors expelled out framework and/or sorbed acidic conditions. This effect induced reduced stability Co(III) when relative proportion corner-sharing linkages increases. In turn, influences structural incorporation different its potential release solution.