Polyaluminosilicate process

DETAILED DESCRIPTION OF THE INVENTION Preparation of the polyaluminosilicates of the invention require the initial preparation of polysilicic acid microgels otherwise known as active silica.
Methods for the preparation of active silica are well described in the book "Soluble Silicates," Vol.
II, by James G.
Vail and published by Reinhold Publishing Co.
, NY, 1960.
In general, the methods all involve the partial acidification usually to about pH 8-9 of a dilute solution of alkali metal silicate such as sodium polysilicate Na.
sub.
2 O.
3.
2SiO.
sub.
2.
Acidification has been achieved using mineral acids, acid exchange resins, acid salts and acid gases.
The use of some neutral salts as activators has also been described.
For the purpose of practicing the present invention, acid deionization of a dilute solution of sodium polysilicate, is preferred although the other methods of activation reported in the literature may also be used.
Iler, in the above stated text at page 288, teaches that solutions containing up to 12 wt.
% SiO.
sub.
2 can be used in the formation of polysilicic acid, the higher percentages requiring rigorous, tightly controlled operating conditions.
While the full range can be used in the practice of this invention, SiO.
sub.
2 concentration in the range of 0.
1-6 wt.
% is preferred.
Acidification using any strong acid exchange resin known in the art, such as disclosed in U.
S.
Pat.
No.
2,244,325 is preferred since it effectively removes the unwanted sodium value of the sodium silicate.
If this sodium value is not removed and sulfuric acid, say, is used for the acidification considerable quantities of sodium sulfate are generated in the product.
This sodium sulfate can be burdensome in maintaining both pollution and corrosion control standards.
The deionization is preferably conducted into the acid range of pH 2.
5-5 although the higher pH ranges of 5-10.
5 may also be employed particularly if higher sodium ion concentration can be tolerated.
In the pH 2.
5-5 range, the polysilicic acid is metastable and conditions are favorable for aggregation of the very small, high-surface-area particles into the desired chain and three dimensional networks described earlier