The Effect of Degree of Polymerization of Silicates on Their Interactions with Cations in Solution

The development of a better understanding of the role soluble silcates play in detergency, mineral beneficiation, enhanced oil recovery, etc., has led us to look carefully at the interactions of soluble silicate species with metal ions in solution. The acidity of ≡Si-OH increases as the complexity of the silica species increases, e.g., pKa for Si(OH)2O2= is 9.91± 0.04 whereas ≡Si-OH on silca gel has a pKa = 6.8± 0.2. Viewing the interaction of metal ions in solution with a soluble silica surface as an ion exchange process, one might expect differences dependent on the degree of polymerization of the silicate anion. Our results indicate that metal ion activities in solution are sensitive to factors related to the anion structure and pH value. The results support Iler's observation that silicate solution begins to absorb multivalent metal ions in solution at pH values roughly two units below the pH at which the metal hydroxide is precipitated