Synthesis of zeolite A from Iranian Hesarbon natural zeolite

Synthesis of pure-form zeolite A (LTA) was studied from Hesarbon mine natural clinoptilolite zeolite using different concentrations of NaOH solution to dissolve Si source, and with addition of sodium aluminate as Al source, to prepare initial gel. The chemical analysis of the clinoptilolite samples shows a SiO2/Al2O3 ratio of 6.29. Before synthesis experiments, the beneficiation methods like desliming and flotation were applied on the samples to remove impurity, improving the ratio to 5.37. Zeolites are generally synthesized by the hydrothermal reaction of sodium aluminosilicate gels in alkaline medium using conventional heating systems. In the synthesis experiments of Hesarbon sample, the effect of important variables such as reaction time, NaOH concentration, weight of sodium aluminate, clinoptilolite to sodium aluminate ratio and temperature were studied. The synthesis experiments results demonstrated that NaOH concentrations in initial gel played an important role in the synthesis. It was found that the higher NaOH concentration was used, the shorter crystallization time of zeolite A was required. The nucleation and crystallization rates, as well as the yield of zeolite A increased as the NaOH concentrations increase. It was found that the zeolite A could be synthesized from clinoptilolite under following conditions: NaOH concentrations, 3 N; the synthesis temperature, 90 ◦C; the corresponding crystallization time, 8 hours; clinoptilolite to sodium aluminate ratio 3/25. The products of the reactions were characterized using XRD, and chemical analysis to confirm zeolite crystallinity and phase purity. The synthesized product SiO2/Al2O3 ratio was 2.4, which is consistent with the ratio of zeolite A.