| 摘要 |
In the preparation of manganese dioxide, suitable for use as a battery depolariser, by the oxidation in aqueous medium of manganese sulphate with an alkali metal chlorate, preferably at 80-95 DEG C., the reaction is carried out in the presence of a catalytically active manganese dioxide, which is obtained either by roasting precipitated manganese carbonate under oxidising conditions, or by leaching with sulphuric acid a manganese oxide in a lower state of oxidation than MnO2 and a higher state than MnO. The amount of catalytic manganese dioxide employed is preferably at least equal to the amount of manganese sulphate. In one process, precipitated manganese carbonate is roasted under oxidising conditions until the major component is manganese dioxide and the remainder manganous. The roast is leached with at least sufficient aqueous sulphuric acid to convert substantially all of the manganous component to manganese sulphate, and the resulting slurry is reacted with sodium chlorate to form further MnO2. The manganese dioxide product is separated, washed with water, and dried. Further manganese carbonate sulphuric acid, and sodium chlorate may be added to the reaction mixture before recovering the manganese dioxide. In another process a material consisting essentially of a manganese oxide in a lower state of oxidation than MnO2 and a higher state of oxidation than MnO, for example Mn2O3 or Mn3O4, is reacted with aqueous sulphuric acid and an alkali metal chlorate. In this process the catalytic MnO2 component is produced in situ by the action of the sulphuric acid on the MnO of the manganese raw material. The manganese raw material may be added in small increments to an aqueous solution of sulphuric acid and sodium chlorate at 85 DEG C.-87 DEG C., or it may be added at low temperatures so that only the reaction between the raw material and the sulphuric acid occurs, and then the temperature raised to 85 DEG C.-87 DEG C. to effect the oxidation. |
