Production of alkali metal silicate having a high silica to alkali metal oxide ratio

Claim 1

A process for increasing the silica:alkali metal oxide weight ratio of aqueous alkali metal silicate solution comprising: (a) providing an electrolytic cell having a cathode compartment and an associated cathode and an anode compartment and an associated anode, said compartments separated by a cation selective permionic membrane; (b) charging aqueous alkali metal silicate solution to the anode compartment, said solution having a silica: alkali metal oxide weight ratio of up to about 2.5:1, a pH of at least 11, whereby to maintain the solution free of colloidal suspension or sol of finely divided silica particles, and a water content of at least 75 percent by weight; (c) charging water or aqueous alkali metal hydroxide solution to the cathode compartment; (d) applying a direct current across the cell to decompose alkali metal oxide at the anode into alkali metal ions and gaseous oxygen and to cause said alkali metal ions to migrate from the anode compartment through the membrane into the cathode compartment therein forming alkali metal hydroxide; (e) withdrawing aqueous alkali metal silicate solution from the anode compartment, said solution having a silica: alkali metal oxide weight ratio of about 3:1 to about 4.5:1 and a pH greater than 10, whereby to maintain the solution free of colloidal suspension or sol of finely divided silica particles; and (f) withdrawing alkali metal hydroxide from and adding make-up water to the cathode compartment.