Polymerization behavior of silicic acid with Fe³⁺, Al³⁺, and Ca²⁺ coexisting ions

Silicic acid was prepared by acid hydrolysis of water-quenched calcium silicate, and Ca²⁺, Al³⁺, and Fe³⁺ were added to investigate the polymerization behavior. Effect order of the three ions on the polymerization was Fe³⁺ > Al³⁺ > Ca²⁺. Due to decreased polymerization rate caused by Fe³⁺ at pH < 3, average diameter of the colloidal particles at pH = 2 was larger than that at pH = 3. New infrared absorption peaks were found at 2360 cm⁻¹ which may be attributed to Ca–OH, Al–O–Si, and Fe–O–Si, respectively, and it was especially obvious for Fe³⁺. For three ions coexisting system, the new peak showed a slight shift to 2370 cm⁻¹. Preventing ability of Fe³⁺ on water binding is much stronger than promoting ability of Al³⁺. Dehydration process of bound water was hindered by adding the three ions, and due to higher bound water content, endothermic peak for Al³⁺ system was stronger. Crystallization process was hindered by Ca²⁺ and Fe³⁺.