J. Cryst. Growth

The supersolubility of silica in supersaturated aluminate solution and the sodium aluminosilicate precipitation nucleation mechanism from the clear solution were investigated by experiment. The obtained semi-empirical expression of the induction (t(ind)) of sodium aluminosilicate precipitation from clear solution is significant for zeolite A membranes synthesis, desilication and. more important for valuating the stability of the supersaturated SiO2 in the aluminate solution during the. hydrolysis operation in the - most used alkaline alumina manufacture. The semi-empirical expressions of the silica supersolubility in clear supersaturated sodium aluminate solution for both homogeneous and heterogeneous nucleation were originally conducted. The homogeneous nucleation predominated with the supersaturation (S) above 6.0, conversely, heterogeneous nucleation with S below 4.0. The inferred activation energy (Ea) of the homogeneous nucleated reaction was 14.9 kJ/mol, and that of the heterogeneous 50.5 kJ/mol. The interfacial tension (gamma(s)) between the precipitate of sodium aluminosilicate and the surrounding aqueous solution was obtained at 15.1 mJ/m(2), negligibly decreased with increasing temperature. It was much larger than the value of 12.4 mJ/m(2) in pure water (J. Phys. Chem. B 105 (2001) 5383), but very much smaller than the estimated value of 38.64-50mJ/m(2) in the solution for traditional zeolite synthesis. (C) 2003 Elsevier Science B.V. All rights reserved.The supersolubility of silica in supersaturated aluminate solution and the sodium aluminosilicate precipitation nucleation mechanism from the clear solution were investigated by experiment. The obtained semi-empirical expression of the induction (t(ind)) of sodium aluminosilicate precipitation from clear solution is significant for zeolite A membranes synthesis, desilication and. more important for valuating the stability of the supersaturated SiO2 in the aluminate solution during the. hydrolysis operation in the - most used alkaline alumina manufacture. The semi-empirical expressions of the silica supersolubility in clear supersaturated sodium aluminate solution for both homogeneous and heterogeneous nucleation were originally conducted. The homogeneous nucleation predominated with the supersaturation (S) above 6.0, conversely, heterogeneous nucleation with S below 4.0. The inferred activation energy (Ea) of the homogeneous nucleated reaction was 14.9 kJ/mol, and that of the heterogeneous 50.5 kJ/mol. The interfacial tension (gamma(s)) between the precipitate of sodium aluminosilicate and the surrounding aqueous solution was obtained at 15.1 mJ/m(2), negligibly decreased with increasing temperature. It was much larger than the value of 12.4 mJ/m(2) in pure water (J. Phys. Chem. B 105 (2001) 5383), but very much smaller than the estimated value of 38.64-50mJ/m(2) in the solution for traditional zeolite synthesis. (C) 2003 Elsevier Science B.V. All rights reserved