| 摘要 |
1,143,336. Sodium silicofluoride. TOYO KOATSIL INDUSTRIES Inc. 23 Jan., 1968 [7 Feb., 1967], No. 3577/68. Heading C1A. Highly pure sodium silicofluoride is prepared from crude phosphoric acid manufactured by treating phosphate containing rock with sulphuric acid, by adding sodium hydroxide or a sodium salt other than the fluoride or hydrofluoride to the phosphoric acid in the presence of sodium fluoride or hydrofluoride. The crude phosphoric acid produced contains 15% to 45% by weight of phosphoric oxide, and 1% to 5% by weight of hydrofluosilicic acid. Sodium salts that may commonly be used are the carbonate, phosphate, sulphate or chloride. The amount of sodium compound used is preferably between 0À5 and 3 times the stoichiometric amount necessary to form the sodium silicofluoride. The amount of sodium fluoride present in the solution does not need to be more than 10g. per litre of solution. Organic impurities in the crude phosphoric acid may be easily removed by filtration, using as a filter aid calcium sulphate crystals formed by hydrating gypsum semihydrate with water or aqueous phosphoric acid. |
