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Influence of alkalinity of the starting system on size and morphology of the zeolite A crystals

The performance of zeolite crystals in different industrial processes often depends on their size and shape. Several physico-chemical parameters can have significant impact on their particulate properties (especially morphology). Amongst the chemical parameters the Si/Al ratio is one of most important variable together with the Na+ ions (alkalinity) content. The present study is devoted to the effect of Na on the morphology of zeolite A (LTA-type) crystals. Initial hydrogels were heated at 80 °C in reactors made of HDPE, under static conditions. After separation by centrifugation, samples of solid and liquid phase were characterized using several analytical methods such as: atomic absorption spectroscopy, X-ray diffraction, laser light scattering, optical, scanning and transmission electron microscopy. The results show that the increase of alkalinity in starting system causes two effects: a) increase of the number of nuclei (crystals) in system through additional nucleation at surface and subsurface area of gel particles, and b) the growth of crystals which have more irregular shape (rounded edges).

zeolite A; morphology; hydrothermal synthesis; crystal size distribution; nuclei distribution; gel matrix

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