Study On The Synthesis Of LSX Molecular Sieves With Crystallization Directing Agent And Its Applications

Low-silica X (LSX) type molecular sieve has large porous and open framwork, in which the speed of ion diffusion and exchange is high. Kuhl and Sherry pointed out that it is possible for LSX to be the additive of wash, however, its cost is high. The Si/Al ratio of normal X zeolite is about 2.5, which restricts its exchange capacity. Thus, to decrease the cost of LSX and the Si/Al ratio of X zeolites have attracted much attention.Using industrial products, low-silica X (LSX) molecular sieves are synthesized by the crystallization directing agent (CDA) method. In this paper we have discussed the influences on LSX's synthsis, such as the composition of the reaction mixture, the aging temperature and time, the crystallization temperature and time, etc. Then the technical parameters of hydrothermal synthesis of zeolites are optimized. The optimum technical conditions are as follows. The reaction mixture ratio is Al₂O₃ : 2SiO₂ : 6M₂O : 96H₂O (M=K, Na) , K₂O/(Na₂O+K₂O)=0.33. Then the mixture was aged at 70°C for 7h. Afterwards, the crystallization process was carried out at 100°C for 3h.With the crystallization directing agent (CDA), LSX, which has high crystallinity and purification, has been synthesized from industrial products. The resultant is characterized by XRD and XRF. It shows that the Si/Al ratio is about 1 and the main cations are Na⁺ and K⁺. The water static adsorption capacity is high to 31.94%.Since the special structure of zeolite, the reversible ion exchange is possible to be taken place. As a result, it can be applied in environment restoration, purification and replacement etc. The ion exchange capability of LSX with Li⁺ and Ca²⁺ was investigated in this paper which guides the utilizing of LSX theoretically.