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Mechanism and kinetics of the growth of zeolite microcrystals. Part 1. Influence of the alkalinity of the system on the growth kinetics of zeolite A microcrystals

Kinetics of crystal growth of zeolite A were measured during the crystallization of zeolite A at 80o C from the amorphous aluminosilicate precursor (1.03 Na_2O•Al_2O_3•2.38 SiO_2•1.66 H_2O) dispersed in 1.2 M (system I), 1.4 M (system II), 1.6 M (system III), 1.8 M (system IV) and 2 M (system V) NaOH solution. Analysis of the experimental results (changes of the concentrations, C_Al , of aluminum and C_Si , of silicon in the liquid phase as well as of the dimension, L_m , of the largest crystals of zeolite A 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. The crystal growth takes place in accordance with the Davies and Jones model of growth and dissolution, and taking into consideration particularities of zeolite crystallizing systems, the kinetics of crystal growth of zeolites may be defined as: dL/dt_c = k_g [C_Al-C_Al^*][C_Si-C_Si^*] where C_Al^* and C_Si^* are the concentrations of aluminum 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.

alkalinity; crystal growth; crystallization; kinetics; mechanism; zeolite A

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