1. Field of the Invention
This invention relates to an electrolysis method for producing chlorine at the surface of an anode and a metal at the surface of a cathode by electrolyzing a molten metal chloride obtained by melting a chloride of a metal more base than hydrogen such as sodium, magnesium, calcium and aluminum.
2. Description of the Prior Art
Electrolysis of molten sodium chloride (Downs method as disclosed in, for example, U.S. Pat. No. 1,501,756), electrolysis of magnesium chloride as disclosed in, for example, U.S. Pat. Nos. 1,567,318 and 1,921,377, and hightemperature electrolysis of aluminum chloride (Alcoa method as disclosed in, for example, U.S. Pat. No. 3,725,222), for example, are known methods of producing metals by electrolysis of molten metal chlorides.
Conventionally, in these electrolytic methods, carbon is used as an anode and iron or carbon is used as a cathode. The carbon anode is consumed forming CO or CO.sub.2 due to an anodic oxidation reaction, and consumption of electric power increases because of the increase in the interelectrode distance. To prevent this, adjustment of the interelectrode distance and replacement of the electrode must be performed periodically. In the Alcoa method for electrolysis of molten aluminum chloride, the consumption of the carbon anode and the formation of sludge are inhibited by limiting the oxide concentration of metal oxide in the molten salt bath to not more than 0.25%, preferably not more than 0.1%, by weight as oxygen thereby to remove the metal oxide in the bath which is a cause of anode consumption, and to maintain the molten salt bath as acidic as possible (e.g., as disclosed in U.S. Pat. No. 3,725,222 corresponding to Japanese Patent Publication No. 15043/77). However, in order to maintain the bath as acidic as possible, the metal oxide must be removed from the bath or the metal oxide content must be reduced, and also the electrolytic cell must be sealed completely so as to prevent entry of moisture and air. The operation and the control of this method are, therefore, complicated.