Investigation of kaolinite structural order in geophagic soils by infrared spectroscopy: an empirical approach

Abstract

Mineralogy and kaolinite structural order in selected geophagic soils were investigated by X-ray diffraction and infra-red (IR) spectroscopy. Structural order was assessed by empirical analysis of IR resolutions and relative intensities of OH stretching and bending vibrations of structural water in kaolinite. Quartz and kaolinite were major constituents, associated with muscovite + microcline + goethite + hematite + anatase ± kaolinite-smectite ± gibbsite. The IR spectra exhibited three characteristic kaolinite peaks at 3697, 3645/50 and 3620 cm⁻¹, poorly resolved OH stretching vibrations with quartz and goethite interferences. The two middle bands expected of theoretical kaolinite were replaced by a low intensity peak at 3645/50 cm⁻¹. Based on spectral analysis the samples were classified as partially ordered. Findings suggest the presence of impurities, high potential for substitution reactions and more vacant sites for cation exchange, necessitating further investigations on the bioavailability of nutrients/toxins for a comprehensive health appraisal.

Keywords:

• infrared spectroscopy
• impurity
• isomorphic substitution
• geophagia
• kaolinite
• structural order

DISCLOSURE STATEMENT

No potential conflict of interest was reported by the authors.