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

Kinetics of crystal growth of zeolite A were measured during the crystallization of zeolite A at 80^o C from different systems, defined by chemical compositions of starting aluminosilicate hydrogels: 2.67Na_2OˇAl_2O_3ˇ1.98SiO_2ˇ122.3H_2O for system I; 1.96Na_2OˇAl_2O_3ˇ1.98SiO_2ˇ121.5H_2O for system II and 2.31Na_2OˇAl_2O_3ˇ2.62SiO_2ˇ163H_2O for system III, and thus by the distribution of Na, Al and Si between the solid and the liquid phase of the systems. 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 during crystallization) have shown that the growth rate, dL/dt, of zeolite A microcrystals can be expressed as: dL/dt = kg [CAl - CAl*][CSi - CSi*], where CAl* and CSi* are the concentrations of aluminum and silicon in the liquid phase which correspond to the solubility of zeolite A at given crystallization conditions. The value of the growth rate constant, kg, depends on the properties of the crystallizing system, especially on the properties of its liquid phase at given crystallization conditions.

Crystal growth; Aluminosilicate hydrogel; Distribution of Na; Al and Si; Zeolite A

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