Mineralogical and crystallochemical analyses of kaolin from Mbengwi (Northwest Region,Cameroon)

Abstract

This study presents a detailed mineralogical and crystallochemical characterisation of clay deposits from Mbengwi (Northwest Region, Cameroon) to evaluate their suitability for industrial applications. Three samples collected at depths of 10.7 m (BGW1), 8.8 m (BGW2) and 6.5 m (BGW3) were analysed using x-ray fluorescence, x-ray diffraction, Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis and differential scanning calorimetry. Across all sampled depths, high-purity kaolinite consistently dominates the mineralogical composition (∼90%), with minor occurrences of illite (1.5%), quartz (3%), goethite (1.3%) and anatase (1.4%). The SiO₂/Al₂O₃ ratio closely aligns with the theoretical value for ideal kaolinite (1.17). The absence of distinct crystalline iron-bearing phases suggests either isomorphic substitution of Fe³⁺ within the kaolinite lattice or the presence of poorly crystalline iron minerals. Crystallinity indices – including the Hinckley Index, the size of the coherent scattering domain (D), the slope ratio and the FTIR-derived P₀ and P₂ factors – indicate a progressive enhancement of structural order with increasing depth. Thermal analyses corroborate this trend: deeper samples exhibit higher dehydroxylation temperatures and sharper endothermic peaks, reflecting least defect density and high kaolinite purity. These findings highlight the superior crystallinity and purity of deeper kaolinitic layers, positioning Mbengwi clays as promising candidates for high-performance applications such as ceramics, paper, catalyst supports and polymer industries.