Process of concentrating aqueous silica sols

Claim 1

A PROCESS FOR CONCENTRATING AN AQUEOUS SILICA SOL WHICH COMPRISES BOILDING OFF WATER FROM AN INITIAL, ALKALINE SILICA SOL HAVING AN INITIAL PH OF 9 TO 10.5 AND A SILICA TO ALKALI OXIDE WEIGHT RATION, EXPRESSED AS SIO2:NA2O, IN THE RANGE OF 50:1 TO 130:1, AND ADDING TO SAID ALKALINE SILICA SOL AND AQUEOUS, ACIDIC SILICA SOL HAVING A PH BETWEEN 2 AND 5.5 AND OBTAINED AS THE EFFLUENT FROM THE PASSAGE OF AN ALKALINE ALKALI METAL-SILICA SOL THROUGH AN ACID ACTIVATED, CATION EXCHANGER, SAID EFFLUENT THEREBY BEING SUBSTANTIALLY FREE OF ALKALI METAL IONS, SAID AQUEOUS, ACIDIC SILICA SOL BEING THE ONLY COMPOSITION ADDED TO SAID ALKALINE SILICA SOL DURING THE EVAPORATION PERIOD, MAINTAINING THE ADDITIONS OF SAID AQUEOUS, ACIDIC SILICA SOL TO SAID ALKALINE SILICA SOL AT A RATE MAINTAINED TO GRADUALLY REDUCE THE PH OF THE AQUEOUS, ACIDIC SOL DURING THE EVAPORATION PERIOD, SAID RATE BEING SUCH THAT THE ALKALINE SOL DURING CONCENTRATED IS MAINTAINED IN AN ALKALINE CONDITION AND WHEREBY THE SIO2:NA2O RATIO GRADUALLY INCREASES DURING THE EVAPORATION PERIOD, AND, WHEN THE CONCENTRATED SOL CONTAINS 18-48* BY WEIGHT SIO2, RECOVERING THE CONCENTRATED SILICA SOL AT AN ALKALINE PH BELOW THE PH OF SAID INITIAL, DILUTE, ALKALINE SILICA SOL.