Kaolinite: A study of the first steps on the dehydroxylation process

I. POLCOWÑUK IRIARTE; N. RENDTORFF; D. RICHARD

La Plata

Workshop; X Workshop on Novel Methods for Electronic Structure Calculations; 2023

UNLP

Kaolin is a natural clay with kaolinite as the main crystallographic phase. The importance ofthis clay is related to its influence in ceramics, materials science, and mineralogy. The industrialuse of kaolinite requires thermal treatments, so it is interesting to understand how metakaolin isformed during the thermal activation of this clay and also to know what are the physics and chemistrymechanisms behind its production [1]. These mechanisms are complex and according to theliterature there is not a general agreement on which is the rate-controlling step in the reaction, andon the atomic arrangement of metakaolinite [2].In this work it is studied the beginning of the dehydroxylation process using calculation methodsbased in Density Functional Theory. Four systems that combine vacancies of an OH group and aH atom in the kaolinite unit cell were proposed, considering each one as a possible first step in thereaction. Using the open source package Quantum ESPRESSO [3], the structure of each system wasoptimized and its energy was analyzed after the optimization. The results were compared betweenthem and with the literature. After that, one system was chosen as the most compatible with thephysical process, and its properties were analyzed. The X-ray diffraction pattern, the vibrationalnormal modes, and the electronic density of states were also studied and compared with those calculatedfor kaolinite.The predicted properties were also compared to experimental data, obtained from a well-crystallizedkaolinite (KGa-1) and a national one (Sur de R´ıo Blanco).The obtained results help to elucidate the beginning of the metakaolin production process and alsohelp to understand the differences between the four proposed systems. The promising results encouragefurther analyses using the same theoretical-experimental methodology in order to continuethe study of the transformation of kaolinite towards its dehydroxylated form.