Electrodialysis Route to Colloidal Silica

The use of electrodialysis as a method of producing colloidal sUica products is potentially a very desirable process in that there is very little acid consumption, virtually no salts are produced which must be disposed of, and the by-products, hydrogen, oxygen, and sodium hydroxide are themselves usefid. 

A Significant portion of the product is left in the reactor and provides particles on which new silica deposits. Some particles leaving the reactor have seen many ( cles some only one. 

FIGURE 12.7 A variation allows production of a broad particle size distribution. 

In this process the silicate Is not completely deionized but rather the flow of the Ion exchange resin and the silicate feed are controlled to give an appropriate level of residual sodium to Induce particle growth 

Process Stream = Sol + Dilute Silicate Circulated at high flow through the area bounded by two membranes. 

---

FIGURE 12.10 Electrodialysis route to colloidal silica described by R.K. Her — U.S Patent 3,668,088. 

---