Inorganic polymer coagulants of metal-polysilicate complex

Cationic metal-polysilicate complexes were proposed for the removal of colloidal or suspended matter as a new category of inorganic polymer coagulants. By means of ultrafiltration, molecular-weight fractionation was performed to learn the degree of polymerization of silicic acid. Staudinger's relationship was confirmed between the molecular weight and the limiting viscosity with respect to the polysilicic acid sol. With the limiting viscosity as the key indicator, polymerization studies were carried out under various conditions. In a strongly acidic region, a polysilicic acid solution of much higher molecular weight was obtainable without gelation for an extended period. Multivalent metal ions were introduced into the polysilicic acid solution obtained to add a charge-neutralizing capability. These two chemical species, i.e. multivalent metal ions and polysilicic acid, comprise a new category of inorganic polymer coagulants. These coagulants have shown a high coagulation effect, greatly superior to that of conventional inorganic coagulants for both turbidity and color removal. Electrophoresis experiments were also performed to characterize the new inorganic polymer coagulants. On the basis of these studies, the coagulation/flocculation mechanism of the new inorganic coagulants is discussed.