Manganese dioxide is a black, highly crystalline metallic substance with the chemical formula MnO2. It occurs naturally as the blue-black mineral pyrolusite.
The most common application for this chemical is as an oxidizer in dry cell alkaline batteries. It also functions as a depolarizer in lithium-ion battery cells. It is also a primary precursor to ferromanganese, an alloy of iron used in the manufacture of high-grade steels and castings.
When swallowed, manganese oxide can cause gastrointestinal irritation. Manganese toxicity can also lead to central nervous system effects, such as tremors and difficulty walking. Manganese exposure can also increase anemia by interfering with iron absorption.
It is also used to make glass, as a colorant and as an oxidizer. It is a component in making faience, majolica, and porcelain. It can be precipitated from the sand of pyrolusite or made synthetically from other compounds such as manganese carbonate, manganese sulfide, and magnesium hydroxide. It is often used in electrotechnics, pigments, browning gun barrels, and as a drier for paints and varnishes, as well as in printing and dyeing textiles.
When discarded, manganese dioxide is classified as a hazardous waste under the Resource Conservation and Recovery Act (RCRA). Hazardous waste generators must consult state and local regulations for guidance on classification. It may be disposed of in an approved landfill or inert waste. The EPA recommends that this chemical is not empty into drains. Doing so may result in contamination of groundwater.