MNO2

Manganese dioxide, MnO2, is an inorganic compound in which manganese is in the +4 oxidation state, bound to oxide. It occurs naturally as the mineral pyrolusite, the most common manganese oxide mineral.

MnO2 exists in several polymorphs, including α-MnO2 and γ-MnO2, which differ in crystal structure. It is a dark brown to black solid and is virtually insoluble in water. It functions as a mild oxidizing agent in many chemical reactions and remains relatively inert under ambient conditions.

Industrial production and occurrence: Pyrolusite is mined as an ore. High-purity MnO2 used in batteries is commonly produced by oxidation of Mn2+ solutions or by the electrochemical process known as electrolytic manganese dioxide (EMD). MnO2 can also be formed by calcining manganese oxyhydroxides.

Applications: The principal use of MnO2 is as the cathode material in alkaline manganese dioxide batteries and zinc–MnO2 primary cells. It also serves as a catalyst for the decomposition of hydrogen peroxide and for certain oxidation reactions, and it is employed as a pigment and as an adsorbent in water treatment to remove impurities.

Safety and environment: MnO2 is relatively low in systemic toxicity compared with many other manganese compounds, but inhalation of fine dust can be hazardous and prolonged exposure may cause respiratory or other health effects. Proper engineering controls and personal protective equipment are advised during handling and processing.