Process for increasing the concentration of a metastable silica sol

Claim 1

IN A PROCESS FOR INCREASING THE SILICA CONCERATION OF A METASTABLE SILICA SOL THE STEPS COMPRISING MIXING WITH A SILICA SOL CONTAINING ULTIMATE SILICA PARTICLES LESS THAN ABOUT 4 MILLIMICRONS IN DIAMETER AND HAVING AN SIO2 CONTENT OF UP TO 4 PER CENT AN ALKALI METAL SILICATE SOLUTION HAVING A SILICA CONCERTRATION OF ABOUT FROM 10 TO 36 PER CENT BY WEIGHT, WITH AGITATION AT THE POINT OF MIXING SUFFICIENT TO CAUSE HOMOGENEITY SIBSTANTIALLY INSTANTANEOUSLY, THE PORPORTION FO SILICATE ADDED BEING NOT MORE THAN ENOUGHT TO MAKE THE ALKALI METAL ION CONTANT OF THE MIXTURE 0.4 NORMAL AND THE TEMPERATURE BEING MAINTAINED BELOW 60* C., REMOVING ALKALI METAL IONS FROM THE MIXED SOL AND SOLUTION BY PASSING THE MIXTURE IN CONTACT WITH A CATION-EXCHANGER IN THE HYDROGEN FROM THE EFFLUENT HAVING A PH BELOW ABOUT 4, AND REPEATING THE PROCESS USING THE EFFLUENT FROM THE ION-EXCHANGER AS THE SILICA SOL TREATED, UNTIL THE SILICA CONCENTRATION OF THE EFFLUENT HAS BEEN BROUGHT UP TO ABOUT FROM 10 TO 20 PER CENT SIO2.