Processes for the manufacture of silica hydrosols

Claim 1

A PROCESS FOR THE PRODUCTION OF SILICA HYDROSOLS WHICH COMPRISES FIRST FORMING AN AQUEOUS SOLUTION CONTAINING SILICA HYDROSOL BY MIXING AN ALKALI METAL SILICATE SOLUTION WITH AN EXCESS OF ACID AND AN AQUEOUS ACID SOLUTION CONTAINING SILICA HYDROSOL SO THAT THE RESULTING MIXTURE HAS A PH BELOW ABOUT 5.0 AND CONTAINS THE ALKALI METAL SALT OF THE ACID AND EXCESS ACID, THEN PASSING THE RESULTING MIXTURE THROUGH A STATIONARY BED OF GRANULAR CATION EXCHANGE MATERIAL TO REMOVE ALKALI METAL IONS FROM THE MIXTURE AND TO REGENERATE ACID FROM THE ALKALI METAL SALT OF THE ACID, WITHDRAWING AN ACID SOLUTION CONTAINING SILICA HYDROSOL FROM SAID STATIONARY BED OF CATION EXCHANGE MATERIAL, REMOVING AS A PRODUCT A MINOR PORTION OF THE WITHDRAWAL ACID SOLUTION CONTAINING SILICA HYDROSOL, MIXING ADDITIONAL ACID AND ALKALI METAL SILICATE SOLUTION WITH THE MAJOR PORTION OF THE WITHDRAWAL ACID SOLUTION TO REPLACE THE ACID AND SILICA REMOVED WITH SAID SILICA HYDROSOL PRODUCT AND TO PRODUCE A MIXTURE CONTAINING ADDITIONALLY FORMED SILICA HYDROSOL AND ADDITIONALLY FORMED ALKALI METAL SALT OF THE ACID AND HAVING A PH BELOW ABOUT 5.0, RECYCLING SUCH LAST-MENTIONED MIXTURE COMPRISING THE MAJOR PORTION OF THE WITHDRAWN ACID SOLUTION CONTAINING SILICA HYDROXOL FOR PASSAGE THROUGH SAID STATIONARY BED OF GRANULAR CATION EXCHANGE MATERIAL FOR REMOVING ALKALI METAL IONS FROM SUCH LAST-MENTIONED MIXTURE AND CONTAINING THE RECYCLING STEP AND WITHDRAWAL OF SILICA HYDROSOL PRODUCT UNTIL THE CATION EXCHANGE MATERIAL IS NEARLY SPENT.