| 摘要 |
<p>In the production of synthetic fluorspar low in SiO2 wherein aqueous hexafluosilicic acid is reacted with calcium carbonate, and the resulting calcium fluoride is filtered off, the improvement which comprises effecting the reaction by adding hexafluosilicic acid to an aqueous suspension of the calcium carbonate at a temperature of about 0 DEG to 40 DEG C, there being present during the reaction at least about 3 times as much water by weight as calcium carbonate. Advantageously the reaction is effected in a plurality of stages, in the first of which the calcium carbonate suspension is reacted with a stoichiometric excess of hexafluosilicic acid up to a pH of about 2 to 3, and after a residence time of about 5 to 30 minutes the pH is adjusted to about 4 to 6 in the second stage by the addition of calcium carbonate.</p> |
