THE MANUFACTURE OF SODIUM FLUORIDE AND SILICA GEL AS SOLID MATERIALS BY THE DECOMPOSITION OF SODIUM SILICO-FLUORIDE

摘要

1295760 Sodium flouride and silica gel ONODA CHEMICAL INDUSTRY CO Ltd 29 May 1970 [29 May 1969] 26108/70 Heading C1A Sodium fluoride and silica gel are produced by treating sodium fluorosilicate with an aqueous solution of ammonium hydroxide with vigorous agitation, the concentration of ammonium hydroxide in the reaction medium during the reaction being not greater than 5 wt. per cent and the total concentration of NH 4 SP+/SP after completion of the reaction being more than 7À5% calculated as NH 3 . In an embodiment of the invention, as illustrated by Fig. I, sodium fluosilicate, either in aqueous solution or as a fine powder, is introduced into a reactive vessel simultaneously with an aqueous solution of ammonium hydroxide and the mixture in the vessel is stirred vigorously at an elevated temperature for about one hour. The slurry discharged from the reactor, after settling is separated in a levigation apparatus and the separated slurries of SiO 2 and NaF filtered, washed, and dried. The filtrate in each case is a solution of ammonium fluoride. The ammonium hydroxide cone. is selected to give a final conc. of NH 4 SP+/SP after reaction greater than 7À5% and the conc. of free NH 3 during reaction is kept as low as possible. The slurry obtained from the process as described may be subsequently reacted with aqueous NaOH, Na 2 SO 4 , or NaCl to increase the yield of NaF and form an aqueous solution of NH 4 Cl, NH 4 OH or (NH 4 ) 2 SO 4 .