Physical chemistry of aluminosilicate gels .1. Influence of batch concentration on chemical composition of the gels

The influence of batch concentration and order of mixing of aluminate and silicate solutions (A, sodium silicate to sodium aluminate solution; B, sodium aluminate to sodium silicate solution) on the distributions of Na, Al, and Si between the solid and the liquid phase of the sodium aluminosilicate gels having batch compositions: 3 Na2O:Al2O3:2 SiO2:Z(I)H(2)O, System I(A,B), 4.15 Na2O:Al2O3:3.47 SiO2:Z(II)H(2)O, System II(A,B), and 9.06 Na2O:Al2O3:8.05 SiO2:Z(III)H(2)O, System III(A,B) were investigated by measuring the concentrations of Na, Al, and Si in both the solid and the liquid phase by atomic absorption spectroscopy. It was found that the molar ratio, [SiO2/Al2O3](S) of the precipitated solid phase (gel) increases with the increase of the molar ratio [SiO2/Al2O3](N) of the system (N = I, II, or III), but the batch concentration, [Al2O3](bN) (determined by the molar ratio [H2O/Al2O3](bN) of the batch at constant molar ratio, [SiO2/Al2O3](N), of the system) does not affect either the molar ratio, [SiO2/Al2O3](S), of the precipitated gel, or the fractions of Na2O, Al2O3, and SiO, distributed between the solid (gel) and the liquid phase. Equilibrium concentrations of Na2O, Al2O3, and SiO2 in both the solid and the liquid phase as well as the amount of the precipitated gel are, for a given system, linear functions of the batch concentration, [Al2O3](bN), and thus on the concentration, [OH-](L), of ''free'' OH- ions in the liquid phase of the batch ([OH-](L) similar to[Al2O3](bN)). The order of mixing of silicate and aluminate solutions does not considerably influence the properties of the gels. (C) Elsevier Science Inc. 1997.