Calcination effects on meta-forms of kaolin and halloysite: Role of Al-Si spinel crystallization in zeolite synthesis

Date

2025-06-01

Author

Paşabeyoğlu, Pelin
Akata Kurç, Burcu

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The role of Al-Si spinel crystallization during high-temperature calcination of kaolin and halloysite was investigated to optimize the direct synthesis of zeolites 4A and 13X without additional silica or structure-directing agents. Differential thermogravimetry (DTG) and in situ synchrotron X-ray diffraction (SR-XRD) tracked dehydroxylation and Al-Si spinel crystallization, revealing complete dehydroxylation at 575 °C for kaolin and 500 °C for halloysite, with spinel crystallization occurring in a range of 900–940 °C for both clays. Calcination promoted the formation of Al-Si spinel and amorphous silica, increasing the Si/Al ratio and enabling control of zeolite composition and porosity. Calcination conditions determined the zeolite type, evolving from pure 4A to a mixture of 4A/13X, and finally pure 13X. The presence of Al-Si spinel in 13X enhanced mesoporosity, introducing voids and channels between micropores and contributing to high BET surface areas (>500 m2/g) with a dual micro/mesoporous structure. This study establishes a direct link between calcination parameters and zeolite properties, highlighting Al-Si spinel's role in phase transitions and porosity development. These findings provide valuable insights for optimizing industrial applications such as adsorption and catalysis.

Subject Keywords

Al-Si spinel crystallization, Dehydroxylation, Halloysite, In situ synchrotron XRD, Kaolin, Zeolite

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https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=105001670251&origin=inward
https://hdl.handle.net/11511/114254

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Test and Measurement Center In advanced Technologies (MERKEZ LABORATUVARI), Article