Dehydroxylation of Kaolinite: Evaluation of Activation Energy by Thermogravimetric Analysis and Density Functional Theory Insights

• Autores: Polcowñuk Iriarte, Iván Aitor; Mocciaro, Anabella; Rendtorff Birrer, Nicolás Maximiliano; Richard, Diego
• Año de publicación: 2025
• Idioma: inglés
• Tipo de recurso: artículo
• Materia: Química; thermal activation; kaolin; kinetic analysis; first-principles calculations; density functional theory; metakaolin
• Institución: Universidad Nacional de La Plata

Abstract: During the thermal treatment of kaolinite, the main mineral phase in kaolin rock, dehydroxylation occurs, forming metakaolin through a process that has significant industrial applications. This study experimentally analyzed dehydroxylation in two kaolinite samples: a well-crystallized reference sample from the Clay Mineral Society and a locally sourced, industrial kaolin sample. The mechanism and kinetic parameters were evaluated from a series of thermogravimetric measurements. Non-isothermal kinetic analysis revealed that dehydroxylation followed a third-order (F3) reaction mechanism, with activation energies (Ea) ranging from 35 to 60 kcal/mol. Additionally, theoretical calculations based on Density Functional Theory were performed on four systems in which a water molecule was removed by combining OH group and H atom vacancies in the kaolinite unit cell. These models represented the onset of dehydroxylation and provided values for the reaction energy Q from first-principles calculations, which served as reference values for Ea. The results confirm that water molecule formation involving both OH at the kaolinite outer surface and inner surface are energetically competitive and highlight the crucial role of structural relaxations following water removal to determine Q values in the range of 30–50 kcal/mol, in very good agreement with the experiments.
Centro de Tecnología de Recursos Minerales y Cerámica
Facultad de Ingeniería