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Influence of Hydrogel "Density" on the Synthesis of Zeolite A

Many parameters can affect crystallization kinetics and particulate properties of the synthesis and product(s). The "density" of the starting mixture (gel dispersed in alkaline solution) is one of them. Keeping constant Na2O/H2O and Al2O3/SiO2 ratios and decreasing SiO2/H2O ratio, one can obtain a series of hydrogels of different "density by mixing of appropriate aluminate and silicate solutions. During crystallization at 80 oC, samples were take out the oven, washed, driedand analyzed using AAS, XRD, LLS, optical and electron microscopy. Results of particle size distribution curves by volume of end products show bimodal distribution in all cases. The size of the largest particles and LV50 value show that high density of the starting hydrogel (H1, H2) gives larger crystals at lower growth rate, while the smaller crystals come from diluted systems (H4, H5) at higher growth rate. But, most of the changes in particulate properties are observed in the population of larger particles by volume. Due to the large number of small particles in all systems, (similar shape and size of maximums around 1 micrometer) the LN50 (the size value under which 50 % of all particles lie) is constant within experimental error (0.773 micrometers, around 1.8 % of average value)

Zeolite A; Synthesis; Hydrogel density

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