Chapter 6: Application of vibrational spectroscopy to the characterization of phyllosilicates and other industrial minerals
J. Madejová, E. Balan and S. Petit
This chapter shows how infrared (IR) and Raman spectroscopies contribute to better understanding of industrial minerals. These non-destructive techniques provide information on the chemical composition, structure, bonding and reactivity of molecules and/or minerals. The basis of vibrational spectroscopy theory including the modelling of the vibrational properties and spectra of minerals from ‘ab initio’ or ‘first-principles’ calculations appear in the first part of the chapter. A brief review of the IR and Raman instrumentations and sampling techniques is introduced as well. In the following sections, the spectra of selected minerals are presented and their interpretation is discussed. Raman spectroscopy is less often used for industrial minerals characterization, therefore the emphasis is on the interpretation of the IR spectra of most common industrial minerals in the middle IR (MIR, 4000–400 cm–1) and near-infrared IR (NIR, 8000–4000 cm–1) regions. The MIR spectra of layered silicates (phyllosilicates), zeolites, carbonates, sulphates and phosphates show well defined absorption bands corresponding to fundamental stretching (n) and bending (d) vibrations of the structural units, e.g. OH, SiO4, CO3, SO4 or PO4 groups. Most of the bands present in the NIR spectra are related to the first stretching overtones (2n) and combination (n þd) modes of the fundamental OH vibrations. The NIR region has been found to be useful at providing information on the crystal chemistry of clay minerals and their modifications upon various treatments as the OH-stretching overtones and combination vibrations are sensitively affected by the variations in the mineral structure. The last part of the chapter is devoted to the utilization of Raman spectroscopy in selected mineralogical applications, such as determination of polymorphs not discriminated by their chemical composition, e.g. TiO2 polymorphs.
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