In situ analysis of kaolin and halloysite dehydroxylation and Al-Si spinel crystallization at high temperatures via synchrotron x-ray diffraction

Date

2024-09-01

Author

Paşabeyoğlu, Pelin
Abdellatief, Mahmoud
Hans, Philipp
Akata Kurç, Burcu

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The production of zeolites from kaolin and halloysite clays involves high-temperature treatments to transform the feedstock.This process leads to the formation of meta-forms (metakaolin and metahalloysite) used as precursors in zeolite synthesis.Specifically, kaolin calcined above 950 °C undergoes Al-Si spinel crystallization and amorphous silica release, impacting theSi/Al molar ratio and subsequently affecting the type of zeolite synthesized [1].This study focuses on the thermal behavior of kaolin and halloysite, employing in situ high-temperature X-ray diffraction atthe SESAME Synchrotron MS/XRD beamline [2]. Samples were heated in quartz capillaries using an Oxford FMB gas blower,following specific protocols: for dehydroxylation analysis, clays were heated to 400 °C at a 5 °C/min ramp, with data collectedevery 25 °C up to 800 °C; for spinel crystallization studies, the heating ramp was maintained at 5 °C/min, with data acquisitionevery 5 °C from 900 to 999 °C. Findings indicate complete dehydroxylation at 575 °C for kaolin (Fig. 1d) and 500 °C forhalloysite (Fig. 1a), and both minerals experienced Al-Si spinel crystallization at 940 °C (Fig. 1c, 1f). An α to β quartz phasetransition was observed between 400 and 575°C (Fig. 1b, 1e).Differential thermogravimetry analysis of the clays aligned with existing literature, while N2 adsorption-desorptionmeasurements of the zeolites revealed high BET surface areas, signifying a hierarchical intercrystalline structure of micro andmesopore formation. The presence of mesoporosity, a result of Al-Si spinel crystallization, was further confirmed through low-angle XRD. This study establishes a direct correlation between the calcination time and the resulting zeolite type, highlightingthe novel in situ analysis of Al-Si spinel crystallization. The unprecedented observation of Al-Si spinel crystallization, notdocumented in previous in situ studies, was of particular significance. These insights advance the understanding of thermaltransformations occurring in clay mineralogy resulting in tailoring the obtained zeolite type.[1] P. Pasabeyoglu, G. Moumin, L. de Oliveira, M. Roeb, B. Akata, Solarization of the zeolite production: Calcination of kaolin asproof-ofconcept, J. Clean. Prod. 414 (2023) 137611. https://doi.org/10.1016/j.jclepro.2023.137611.[2] M. Abdellatief, M. Al Najdawi, Y. Momani, B. Aljamal, A. Abbadi, M. Harfouche, G. Paolucci, Operational status of the X-raypowder diffraction beamline at the SESAME synchrotron, J. Synchrotron Radiat. 29 (2022) 532–539.https://doi.org/10.1107/S1600577521012820.

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https://hdl.handle.net/11511/117336

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Test and Measurement Center In advanced Technologies (MERKEZ LABORATUVARI), Conference / Seminar