The reaction mechanism between soluble silicic acid and aluminum in natural water was studied by the detection of concentrations of monomer and soluble aluminum. The concentrations of aluminum were determined by an 8-hydroxyquinoline fluorometric method, and the mechanism was confirmed by thermodynamic calculation. The results indicated that both the monomer and polymer silicic acids mainly reacted with the monomer aluminum to form soluble aluminosilicates. The capacity of combination between monomer silicic acid and monomer aluminum was weak, while it was stronger between the polymer silicic acid and monomer aluminum and the products were mainly bidentate or tridentate coordination compounds. During the reaction process, pH played an important role that the reaction could be notably promoted in slightly alkaline solution.

Key words: aluminosilicate salt, natural water, silicic acid, polymer silicic acid, fluorometric method