Manufacture of sodium fluoride

Claim 1

THE METHOD OF PREPARING SILICA-FREE SODIUM FLORIDE COMPRISING THE STEPS OF ADDING TO FLUOSILICIC ACID AT A TEMPERATURE OF ABOUT 50-90*C. AN EQUIVALENT AMOUNT OF AMMONIA, ADJUSTING THE PH TO ABOUT 8-9 BY FURTHER ADDITION OF AMMONIA, THEREBY PRODUCING A SLURRY OF SILICA IN AN AQUEOUS SOLUTION OF AMMONIUM FLUORIDE, FILTERING SAID SLURRY TO REMOVE SILICA, COOLING THE FILTRATE TO ABOUT ROOM TEMPERATURE, ADDING THERETO SODIUM CHLORIDE EQUIVALENT TO THE AMMONIUM FLUORIDE WHEREBY A SLURRY OF SOLID SODIUM FLUORIDE IN AQUEOUS AMMONIUM CHLORIDE SOLUTION IS FORMED, FILTERING THE SLURRY TO REMOVE SAID SOLID SODIUM FLUORIDE, AMIXTING WITH THE FILTRATE THE FILTRTATE FROM THE AMMONIUM CHLORIDE FILTRATION STEP DESCRIBED BELOW COMPRISING AN AQWUEOUS SOLUTION OF AMMONIUM CHLORIDE AND SODIUM FLORIDE, EVAPORATING THE RESULTING MIXED SOLUTION TO YIELD A SLURRY OF SODIUM FLUORIDE AND AMMONIUM CHLORIDE IN AN KAQUEOUS SOLUTION SATURATED WITH RESPECT TO BOTH SALTS, ADDING SUFFICIENT ANHYDROUS AMMONIA TO DISSOLVE THE AMMONIUM CHLORIDE, THEREBY DEPRESSING TH E SOLUBILITY OF SODIUM FLURIDE, FILTERING OFF THE SODIUM FLUORIDE, EVAPORATING THE AMMONIA FROM THE FILTRATE, THEREBY CAUSING AMMONIUM CHLORIDE TO CRYSTALLIZE, FILTERING OFF THE AMMONIUM CHLORIDE, RETURNING THE FILTRATE TO THE FILTRATE FROM THE FIRST STEP ABOVE, AND WASHING THE SODIUM FLURIDE RESIDUES FREE OF SOLUBLE SALTS, THEREBY OBTAINING SUBSTANTIALLY PURE SODIUM FLUORIDE.

Claim 2

THE METHOD OF PREPARING SILICA-FREE SODIUM FLORIDE COMPRISING THE STEPS OF ADDING TO FLUOSILICIC ACID AT A TEMPERATURE OF ABOUT 50-90*C. AN EQUIVALENT AMOUNT OF AMMONIA, ADJUSTING THE PH TO ABOUT 8-9 BY FURTHER ADDITION OF AMMONIA, THEREBY PRODUCING A SLURRY OF SILICA IN AN AQUEOUS SOLUTION OF AMMONIUM FLUORIDE, FILTERING SAID SLURRY TO REMOVE SILICA, COOLING THE FILTRATE TO ABOUT ROOM TEMPERATURE, ADDING THERETO SODIUM CHLORIDE EQUIVALENT TO THE AMMONIUM FLUORIDE WHEREBY A SLURRY OF SOLID SODIUM FLUORIDE IN AQUEOUS AMMONIUM CHLORIDE SOLUTION IS FORMED, FILTERING THE SLURRY TO REMOVE SAID SOLID SODIUM FLUORIDE, AMIXTING WITH THE FILTRATE THE FILTRTATE FROM THE AMMONIUM CHLORIDE FILTRATION STEP DESCRIBED BELOW COMPRISING AN AQWUEOUS SOLUTION OF AMMONIUM CHLORIDE AND SODIUM FLORIDE, EVAPORATING THE RESULTING MIXED SOLUTION TO YIELD A SLURRY OF SODIUM FLUORIDE AND AMMONIUM CHLORIDE IN AN KAQUEOUS SOLUTION SATURATED WITH RESPECT TO BOTH SALTS, ADDING SUFFICIENT ANHYDROUS AMMONIA TO DISSOLVE THE AMMONIUM CHLORIDE, THEREBY DEPRESSING TH E SOLUBILITY OF SODIUM FLURIDE, FILTERING OFF THE SODIUM FLUORIDE, EVAPORATING THE AMMONIA FROM THE FILTRATE, THEREBY CAUSING AMMONIUM CHLORIDE TO CRYSTALLIZE, FILTERING OFF THE AMMONIUM CHLORIDE, RETURNING THE FILTRATE TO THE FILTRATE FROM THE FIRST STEP ABOVE, AND WASHING THE SODIUM FLURIDE RESIDUES FREE OF SOLUBLE SALTS, THEREBY OBTAINING SUBSTANTIALLY PURE SODIUM FLUORIDE.