Comparative study of physicochemical properties of geopolymers prepared by four Moroccan natural clays

Abstract

The present work concerns the development of geopolymer materials based on natural clays rich in kaolinite, muscovite and pyrophyllite. The aim was to study the effect of the nature and fraction of the clay minerals composing the raw sample on the physico-chemical properties of the prepared geopolymers, viz., the matrix geopolymer phase fraction, particle size distribution, density, compressive strength and the adsorption capacity of methylene blue (MB) as a cationic dye model. The raw starting clays, their meta-clay phases calcined at 800 °C, and the prepared geopolymers were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), particle size distribution (PSD) via laser diffraction method, and scanning electron microscopy (SEM). The matrix geopolymer fraction phase in the samples was qualitatively determined by the analysis of the spectra obtained by 27Al and 29Si solid-state NMR. The results showed that kaolinite-rich clay produced more geopolymer than clays with high phase fractions of muscovite or pyrophyllite and low kaolinite. The highest compressive strength was given by the clay that contained 26.7 % of calcite due to formation of calcium silicate hydrate phase. The maximum adsorption capacity of MB was obtained by the samples have a more heterogeneous surface morphology due to presence of unreacted muscovite and/or pyrophyllite in raw starting clay.