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Effect of Dry Grinding of Pyrophyllite on the Hydrothermal Synthesis of Zeolite Na-X and Na-A

Zeolite Na-X and Na-A were synthesized by mechanochemical activation of pyrophyllite and pyrophyllite-gibbsite mixture followed by hydrothermal reaction in NaOH solution at 75°C under atmospheric pressure. The formation of zeolite Na-X and Na-A was depended on the degree of activation caused by grinding; i.e., grinding accelerated the dissolution of loosely bonded Si substances rather than Al ones of the ground pyrophyllite particles leading the Si/Al molar ratio close to 1.2, which is favorable for the formation of zeolite Na-X. The mixed grinding of pyrophyllite and gibbsite enabled us to synthesize zeolite Na-A monophase. In the early stage of grinding within 60min, the hydroxysodalite (HS) phase was detected, however, HS disappeared completely when the grinding time extended to 120min. The highest crystallinity (I/I0 )o f zeolite Na-A synthesized was estimated to 0.93 at the mixture with Si/Al molar ratio of 1.2. [doi:10.2320/matertrans.M2014127]