Manganese - Electrochemical Manufacture, Importance and Applications

Manganese is mainly utilized as an alloy constituent in the steel industry as ferromanganese and silicomanganese. Pure metallic manganese is required in smaller quantities as an alloy constituent for copper, aluminum and special steels. 

The production of a ca. 97% pure manganese metal by reduction of low iron content manganese ores with silicon, which is not dealt with here, is industrially less important than its electrochemical manufacture. The estimated worldwide production capacity for the electrolytic manufacture of manganese in 1988 was 77 10 t/a. 

A highly purified manganese sulfate solution (see Section 3.5.1.3.1) serves as the electrolyte. The cathodic electrolyte contains 30 to 40 g/L manganese sulfate and 125 to 150 g/L ammonium sulfate and the manganese depleted anodic electrolyte 10 to 20 g/L manganese sulfate, 25 to 40 g/L sulfuric acid and 125 to 150 g/L ammonium sulfate. The anodes consist of lead alloyed with 1% silver, the cathodes of stainless steel or Hastelloy, type 316. The cells are operated at 35 to 40°C, a cathodic current density of 2 to 5.5 A/dm and a potential of 5V. The yield ba.sed on electricity consumed is 50 to 70%. 

Cathodically, hydrogen ions are discharged as well as manganese ions. Anodically, oxygen is formed together with considerable quantities of manganese(lV) oxide, which precipitate and have to be removed. 

When the manganese layers on the cathodes reach a thickness of 1 to 4 mm, the cathodes are removed and the manganese chipped off and dried. It has a purity of over 99.6% with oxygen and sulfur as its main impurities. Most of the other impurities are present in concentrations below 20 ppm. 

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