Synthesis of zeolites A and P from 1:1 and HS from 2:1 clays

This paper deals with synthesizing zeolite A and P using kaolinite as starting material and zeolite HS from smectite. A specific hydrothermal reactor, (allowing the control pH>9, temperature and a continuous stirring of the sample in the NaOH solution) was used to achieve these syntheses. Zeolites A and P were synthesized using respectively a well crystallised kaolinite (KTM), a poorly crystallised kaolinite (KGa₂) and metakaolinites derived from them by heating kaolinites at 500°C and 900°C. Zeolite HS was synthesized using a 2:1 clay mineral (SWy). The synthesis is obtained by reacting heated-smectite at 900°C with NaOH solution at T=120°C and pH >9. HS was formed from the 6th day in the optimal conditions of crystallization corresponding to 120°C and pH=9. The intermediate phases and final products were characterized by X-ray diffraction and high-resolution ²⁹Si and ²⁷Al MAS NMR spectroscopy.