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Influence of concentrations of aluminum and silicon in the liquid phase on the growth kinetics of zeolite A and X microcrystals

Kinetics of crystal growth of zeolites A and X were measured during their crystallization at 80o C from the amorphous aluminosilicate precursor (1.03 Na2O• Al2O3• 2.38 SiO2• 1.66 H2O) dispersed in 1.4 M NaOH solution (system &Oslash ; ), containing 0.046 mol dm-3 NaAlO2 (system A1), 0.092 mol dm-3 NaAlO2 (system A2), 0.136 mol dm-3 NaAlO2 (system A3), 0.034 mol dm-3 Na2SiO3 (system S1), 0.068 mol dm-3 Na2SiO3 (system S2), and 0.102 mol dm-3 Na2SiO3 (system S3). Only zeolite A crystallizes from the systems &Oslash ; , A1, A2, A3 and S1, a mixture of zeolites A and X crystallizes from system S2, and pure zeolite X crystallizes from system S3. Analysis of the experimental results (changes of the concentrations, CAl, of aluminum and CSi, of silicon in the liquid phase as well as of the dimension, Lm, of the largest crystals of zeolite A and X during crystallization) have shown that the growth rate of zeolite A crystals is size-independent, and 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. Influence of the composition of the liquid phase of crystallizing system on the course of crystallization process and on the growth rates of zeolite A and zeolite X crystals are discussed in term of possible distribution of aluminate, silicate and/or aluminosilicate anions in the liquid phase.

Zeolite A; Zeolite X; Aluminate; Silicate; Crystallization; Crystal growth

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