| 摘要 |
The present invention relates to a method for purifying silica waste obtained in the manufacture of aluminium fluoride from hexafluosilicic acid and aluminium hydroxide, whereby the silica, is subjected to an acidic leaching at a pH below 3 to leach out part of the fluorine and substantially all the aluminium present in said waste, and is thereafter subjected to an alkaline leaching at pH 8.5-11.5 to leach out remaining fluorine present in said waste. The leachings are preferably carried out at elevated temperatures, normally 60 DEG -90 DEG C., and for a time sufficient to considerably reduce the contents of aluminium and fluorine, normally 1-3 hrs. The silica obtained is highly reactive and can be used as such or transformed into sodium silicate by a reaction with sodium hydroxide. The contents of fluorine and aluminium can be transferred to a process for the production of cryolite or similar compounds. |
