Determination of the phase composition of partially dehydroxylated kaolinites by modelling their X-ray diffraction patterns

Abstract

Modelling of experimental X-ray diffraction (XRD) patterns is used to determine the phase composition of partially dehydroxylated kaolinite samples. To identify unambiguously the presence of two or three phases in the heated kaolinite samples, the full range of their XRD patterns has to be analysed. Two different kaolinites, from Imerys (UK) and from Georgia (USA; KGa-21), were studied. The heating temperatures were selected to cover the entire range of dehydroxylation for both kaolinites (400–550°C for Imerys and 400–495°C for KGa-21). Two different dehydroxylation pathways were observed. At each stage of partial dehydroxylation, the kaolinite from Imerys consisted of the original, non-dehydroxylated kaolinite and of a fully dehydroxylated phase, metakaolinite. During partial dehydroxylation of kaolinite KGa-21, each product formed at a given heating temperature consisted of three phases: the original kaolinite; a dehydroxylated phase, metakaolinite; and a phase with diffraction features corresponding to a defective kaolinite-like structure. To determine the content of metakaolinite in a partially dehydroxylated specimen, its experimental XRD pattern was reproduced by the optimal summation of the diffraction patterns of the initial kaolinite and metakaolinite. A procedure that reveals the basic diffraction features of the third phase is suggested. The XRD patterns and thus the structures of the metakaolinites formed after dehydroxylation of the Imerys and KGa-21 samples differ substantially. The conventional determination of the initial kaolinite and metakaolinite contents in partially dehydroxylated kaolinite based on the analysis of basal reflections and weight losses may lead to overlooking the formation of the intermediate phases.

Enhanced alumina extraction from kaolin by thermochemical activation using charcoal

“…Based on the TGA/DSC curves of the kaolin-limestone mixture (Fig. 1a), as well as on their previously examined thermal characteristics during the phase transformations of the precursor materials in this sintered mixture (Drits et al , 2019; Húlan et al , 2019; Karbalaei Saleh et al , 2019; Chalouati et al , 2020; ElDeeb et al , 2020a), three main significant regions of the well-defined weight losses on the TGA curve were considered as the initial (or datum) state for monitoring the thermal changes (i.e. before the addition of charcoal).…”

“…Based on the TGA/DSC curves of the kaolin-limestone mixture that shown in Fig. 1A, as well as on their previously examined thermal characteristics during the 15 phase transformations of the precursor materials in this sintered mixture (Chalouati et al, 2020;Drits et al, 2019;ElDeeb et al, 2020a;Húlan et al, 2019;Karbalaei Saleh et al, 2019), the three main significant regions of the well-defined weight losses on the TGA curve were considered as the initial (or datum) state for monitoring the thermal changes (i.e., before the charcoal addition 0 %). Concisely, the AB region was appeared at temperature below 200 °C, the BC region was emerged above 450 °С and the CD region was existed within the range of 650 °C -850 °C.…”

On the Unusual Temperature Dependence of Kaolinite Intercalation Capacity for N-methylformamide

“…Three kaolinite samples were considered in this study: KGa-1b and KGa-2 obtained from the Source Clays Repository of The Clay Minerals Society, and Hywite Alum raw kaolinite from Imerys, UK. The latter was a sample included in recent studies by Drits et al (2019Drits et al ( , 2021 and kindly provided by V.A. Drits.…”

Arcillas caoliníferas: elaboración de geopolímeros con arena de caolín

“…Se observa que el pico con mayor intensidad pertenece al cuarzo, en 30.91° 2θ, los siguientes picos significativos se encuentran en 24.22 ° y 25.44° 2θ, el primero comparte las fases de dickita y cuarzo, mientras que el siguiente comparte las fases caolinita y cristobalita. Se han observado patrones similares en otros trabajos de investigación, (Tironi et al, 2012), (Dewi et al, 2018), (Hernández Pérez, 2017) y (Drits et al, 2019), con la diferencia en que, el pico mayoritario es de caolinita obteniendo relaciones SiO2/Al2O3 entre 1.17 a 1.24, indicando tratarse de un caolín, ver tabla 1. Otros trabajos (Torres et al, 2010), (Nouri & Masoumi, 2020), presentan difractogramas con mayor intensidad en el pico de cuarzo, con una relación SiO 2 /Al 2 O 3 de 2.86 y de 3.53, los cuales entran en la clasificación de arena de caolín.…”