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Kinetic Analysis of Crystal Growth of Zeolite A

Changes of the concentrations, CAl, of aluminium and CSi, of silicon in the liquid phase as well as of the dimension, Lm, of the largest crystals were measured during the crystallization of zeolite A from the amorphous aluminosilicate precursor (1.03 Na2O•Al2O3•2.38 SiO2•1.66 H2O) dispersed in alkaline solutions (1.2 or 1.4 M NaOH solution) containing or not dissolved Al2O3 and/or SiO2 of appropriate concentrations. Analysis of the relationship between the concentration factors f(C) = f(CAl,CSi) relevant for different growth models and crystal growth rate of zeolite A have shown that the that the growth is governed by the reaction of monomeric and/or low-molecular aluminate, silicate and aluminosilicate anions from the liquid phase on the surfaces of growing zeolite crystals, and hence that the kinetics of the growth rate of zeolite A crystals may be expressed as: dL/dtc = kg [CAl-CAl(eq)][CSi-CSi(eq)] = kg f(C), where tc is the time of crystallization, CAl(eq) and CSi(eq) are the concentrations of aluminium and silicon in the liquid phase which correspond to the solubility of zeolite A at given crystallization conditions and kg is the rate constant of the linear growth of zeolite A crystals.

Zeolite A; Crystallization; Crystal growth; Mechanism; Kinetics

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