Non Metallurgical Uses

The most important non-metallurgical application of manganese is in the form of manganese dioxide, which is used as a depolariser in dry-cell batteries. Dry cell consumption in the world exceeds 20 billion units per year. The way manganese works in batteries is simple. In the battery cell, the anode and cathode are essentially humid. During discharge, hydrogen generated at one of the electrodes coats the latter with a gas film, preventing any further wetting, hence cutting off electrical generation. The role of the manganese dioxide is to oxidise the hydrogen and form water. The rate at which this occurs depends on the reactivity of the dioxide.

The Leclanché cell, incorporating this process, was first developed in 1868. Today a zinc can is used as the anode, and the cathode is a rod made of a mixture of acetylene carbon black surrounded by manganese dioxide. A paste of ammonium and zinc chloride is used for the electrolyte. The manganese dioxide, as has been noted, acts as the depolariser.

In the alkaline Mn0₂ zinc cell, which was put on the market in the 1950's, the cathode (Mn0₂/C) is pressed against the inside wall of a steel container, and the anode is made from zinc powder. Potassium hydroxide serves as the electrolyte. This type of cell has a very low resistance and impedance, giving under certain conditions greater service life than the standard cell. Another cell used for specific purposes is the magnesium chloride-manganese dioxide cell developed for military applications.

Naturally occurring manganese dioxides (NMD) can be used in standard cells. Improved manganese dioxide grades required in high performance cells are obtained synthetically. The products are named after the processes used. EMD, or electrochemical manganese dioxide, is made electrochemically; CMD, or chemical manganese dioxide, is produced by a purely chemical process. Combined production of both synthetic types is approximately 200 thousand tons per year, and is growing rapidly.

The market for natural manganese dioxide is about 180-200 thousand tons per year, but very few ores have the properties required for the manufacturing of dry cells. The major producing countries of natural Mn0₂ are Gabon, Brazil, China, Mexico, and India. These “natural grade battery” ores are ground into a fine powder before being used directly in the cathode mixture.