Spectral response (VNIR-SWIR) associated to isomorphic substitutions in the octahedral sheet of the smectites.

In the present work, a chemical and mineralogical study of high purity bentonites has been done. The mineralogical characterization has been carried out by means of X-ray diffraction (XRD) and visible-near infrared and short wave spectroscopy (VNIR-SWIR). The chemical characterization has been conducted by Activation Laboratories Ltd., Ontario (Canada), using FUS-ICP to analyse mayor elements. The aim of this work was to determine the relationship between the spectral response and the chemical elements related to the isomorphic substitutions in the smectites’ sheets.

According to the X-ray study, the 7 samples studied are bentonites with high purity mainly composed of smectites (5 dioctahedral and 2 trioctahedral) and a very low proportion of impurities such as quartz or plagioclase. The VNIR-SWIR study showed the characteristic absorption features of the phyllosilicates. Furthermore, small differences between samples in the wavelength range studied were observed.

For the statistical analysis of the data, the second derivate of the spectra was calculated to obtain the position and the intensity of the absorption features. Wavelength-ranges were defined for each absorption feature. The statistical treatment of the intensity and position of the defined features together with the percentage of the oxides of the major elements of the samples showed significant relationships between the different absorption features and elements of octahedral sheet.