Characterization of raw and thermally treated Nigerian kaolinite-containing clays using instrumental techniques

Abstract

Thermal behavior, surface area, oxide, mineralogical composition, and structural functional groups of raw and thermally treated five local kaolin clays [Ijero-Ekiti (IJ), Ikere-Ekiti (IK), Isan-Ekiti (IS), Abusoro (AB) and Odigbo (OD)] from two states in South-West Nigeria were studied in order to determine their potential uses. These properties were measured using thermogravimetric analysis coupled with differential thermal analysis (TGA/DTA), surface area and porosity analysis, X-ray fluorescence (XRF), X-Ray Diffractometry (XRD) and Fourier Transform infra-red spectroscopy (FTIR) respectively. The TGA/DTA showed major mass losses and broad endothermic bands at temperatures 390–700 °C, which were associated with dehydroxylation of kaolinite and other clay minerals. Thermal treatment increased the surface area of the raw clays. The XRF results showed oxides of kaolinite, illite, quartz, feldspar, hematite, anatase and the phases were confirmed by XRD. The FTIR spectra displayed the characteristic absorption bands of the minerals. Combining the obtained results, Ijero-Ekiti clay was identified as feldspar (albite)-quartz containing clay, Ikere-Ekiti and Isan-Ekiti clays as kaolinite-dominated clays, Abusoro clay as kaolinite-illite-montmorillonite-containing clay and Odigbo clay as kaolinite-illite-containing clay. The TGA/DTA, XRD and FTIR indicated that crystalline kaolinite in the clays were converted into amorphous metakaolinite after thermal treatment. Based on the properties displayed, clays from IK, IS, AB and OD deposits can be thermally treated to form useful supplementary cementitious and geopolymer materials to make binders in building and construction while clay from IJ deposit can be a potential raw material for ceramic production.