Process for producing finely-divided silica

Claim 1

IN A PROCESS FOR PRODUCING FINELY-DIVIDED SILICA BY THE HRDROLYSIS OF SILICON FLUORIDE IN THE VAPOR PHASE, THE METHOD OF RECOVERING AND REUSING THE BY-PRODUCT, FLUORINECONTAINING GASES FROM SAID HYDROLYSIS REACTION AFTER THERI SEPARATION FROM THE FINELY-DIVIDED SOLID SILICA PARODUCT WHICH COMPRISES SCRUBBING THE GASES FROM SAID HYDROLYSIS REACTION WITH A FLUID SLURRY FORMED BY MIXING A CRUDE SILICEOUS MATERIAL WITH AN AQUEOUS SOLSUTION OF A FLUORIDE SALT OF A METAL SELECTED FROM THE GROUP CONSISTING OF POTASSIUM, SODIUM, RUBIDIUM AND ALUMINUM THEREBY PRECIPITATING THE FLUORINE VALVES OF SAID GASES IN THE FORM OF THE RELATIVELY INSOLUBLE FLUOSILICATE SALT OF SAID METAL FILTERING THE LIQUID EFFLUENT FROM SAID SCRUBBING STEP TO REMOVING THE PRECIPITATED AND INNSOLUBLE SOLIDS FROM THE LIQUID PORTION OF SAME, CALCINING SAID REMOVED SOLIDS TO DECOMPOSE THE FLUOSILICATE SALT OF SAID REMOVED SOLIDS TO THEREIN INTO SILICON FLUORIDE VAPORS AND A SOLID RESIDUE AFIG-01 CONTAINING THE FLUORIDE SALT OF SAID METAL, REMOVING AND RECYCLING THE SUBSTANTIALLY PURE SILICON FLUORIDE VAPORS THUS EVOLVED TO THE SAID HYDROLYSIS REACTION, AND RECYCLING THE SOLID RESIDUE OF FLUORIDE SALT OF SAID METAL AS WELL AS THE LIQUID FILTRATE REMOVED FROM SAID SCRUBBING STEP EFFLUENT TO THE MAKE-UP OF ADDITIONAL FLUID SLURRY FOR SAID SCRUBBING STEP.