Pyrolusite, structure

Manganese dioxide, a grey to black solid, occurs in ores such as pyrolusite, where it is usually nonstoichiometric. When made by the action of 02 on Mn at a high temperature, it has the rutile structure found for many other oxides M02 (e.g., those of Ru, Mo, W, Re, Os, Ir, and Rh). However, as normally made by heating Mn(N03)2-6H20 in air ( 530°C), it is nonstoichiometric. A hydrated form is obtained by reduction of aqueous KMn04 in basic solution. Manganese(IV) occurs in a number of mixed oxides. 

During the synthesis of OMS-1 and OL-1, several other phases can be produced. In particular, psilomelane, pyrolusite and ramsdellite can be formed. Pyrolusite has a composition of Mn02 which has a simple tetragonal rutile structure... 

Derivation (1) Natural as pyrolusite and as a special African ore of different atomic structure used exclusively for the battery grade (2) by electrolysis (3) by heating manganese oxide in presence of oxygen (4) by decomposition of manganese nitrate. 

The relatively high specific surface of birnessite and cryptomelane may be in part attributed to their porous nature. An ethylene glycol monoethylether molecule has a cross-sectional area of 0.4 nm (Eltantawy and Arnold, 1973) and it, thus, could penetrate the pores in the structure of birnessite and cryptomelane. This would further explain why the specific surface of birnessite and cryptomelane and their rate constant for the depletion of As(III) are much higher than those for pyrolusite. 

Schematic view of a Cotion-deficienf intergrowth structure of romsdellite ond pyroluiite, with vacancy clustering in the pyrolusite zone. Projection onto the (001) plone.

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