| abstract |
Crude sodium hexafluorosilicate containing gypsum as a principal impurity can be refined economically with a minimized loss of fluorine by first making the crude fluorosilicate in the form of an aqueous slurry react with an alkali metal compound such as sodium carbonate or sodium hydroxide to form a soluble sulfate, and then treating the solid component of the reaction product with an acid solution in the presence of sodium ion, preferably at elevated temperatures near boiling point, to form a soluble calcium salt and crystallize sodium hexafluorosilicate. Sea water may be used both as the aqueous medium for the slurry in the first step and as the source of the sodium ions in the second step. |