Advances in the characterization of industrial minerals
The use of minerals by man is as old as the human race. In fact the advancement of human civilization has been intimately associated with the exploitation of raw materials. It is not by chance that the distinction of the main historical eras is based on the type of raw materials used. Hence the passage from the Paleolithic and Neolithic Age to the Bronze Age is characterized by the introduction of basic metals, mainly copper, zinc and tin, to human activities and the Iron Age was marked by the introduction of iron. Since then the use of metals has increased and culminated in the industrial revolution in the mid-eighteenth century which marked the onset of the industrial age in the western world. However, during the past 50 years, although metals were equally important to western economies as they had been previously, the amount of metals extracted annually in western countries has decreased significantly and metal mining activity shifted mainly to third world countries (in Africa, South America, Asia) and Australia, due to economic and environmental constraints. At the same time the role of industrial minerals has become increasingly important for the western economies and today, in developed EU countries, the production of industrial minerals has surpassed by far the production of metals. In some EU countries, metal mining activities have stopped completely. The importance of industrial minerals is expected to increase further in the future.
Application of Vibrational Spectroscopy to the Characterization of Phyllosilicates and other Industrial Minerals
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Published:January 01, 2010
Abstract
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 (v) and bending (δ) 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 (2v) and combination (v + δ) 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.
