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, SiO 4 , CO 3 , SO 4 or PO 4 groups. Most of the bands present in the NIR spectra are related to the first stretching overtones (2 v ) 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 . TiO 2 polymorphs.

Abstract Clay minerals have long been recognized as playing an important role in industry, such as foundry binding sands, paper production, ceramics and refractory materials, civil engineering, waste management and many more. Clay surfaces act as Lewis and Brensted acids and are naturally occurring source of inorganic catalysts that facilitate a number of organic reactions (e.g., Adams and Clapp, 1986 ; Brown, 1994 ; Breen et al., 1995a , 1997). Clays are important in areas of environmental concern, for example, in controlling migration of pesticides through soil (e.g., Sawhney, 1996 ; Johnson, 1996; Stucki, 1997 ; Moronta et al., 2002 ; Sheng et al., 2002 ). Various chemical and physical-mechanical properties, such as cation exchange capacity (CEC), porosity, and permeability, of the raw and/or modified materials are frequently studied to optimize the utilization of clay minerals. However, the occurrence of new deposits as well as new industrial applications of these minerals, mean that new information on both raw and modified clays will always be required. Bentonites are exceptional among naturally occurring clay ores due to properties such as high cation exchange capacity, high surface area, the ability to swell in water and their capacity to sorb large quantities of inorganic and organic chemicals. They are plastic, impermeable, and have a high viscosity when suspended in water. The largest volumes of bentonites for industrial uses are in foundry moldings, geological explorations as a component for drilling fluids, in civil and geological engineering as barriers or liners under the reservoirs and waste disposal sites and in chemical industry for the manufacture of materials with sorptive and catalytic properties ( Grim, 1968 ; Grim and Guven, 1978 ; Kendall, 1996 ). A substantial amount of bentonites is currently used as adsorbents for pet’s litters. The main components of bentonites are minerals from the smectite group, which substantially affect the properties (CEC, swellability and surface area) and uses of the clay ore. Smectites are formally defined as the group of phyllosilicates with layer charge between 0.4 and 1.2 e − per unit cell, arising from the non-equivalent substitution of central atoms in layers with lower valence cations. The structure of smectites consists of 2:1 layers formed by two tetrahedral sheets linked with an octahedral sheet. Tetrahedral sheets contain normally Si, Al or Fe as central atoms. Two types of octahedral sheets occur in smectites: the dioctahedral type (e.g., in montmorillonite or nontronite) where two-thirds of the octahedral sites are occupied mainly by trivalent cations, e.g., Al (III) or Fe (III), and the trioctahedral type (e.g., in hectorite or saponite), with most of the sites occupied by divalent cations, such as Mg (II). The negative charge of the layers is balanced by hydrated exchangeable cations (mostly Ca 2+ , Mg 2+ , Na + ) located in the interlayer space between adjacent sheets. The extent of hydration varies greatly and depends on many factors related to the composition of the layers and the nature of interlayer cations.

Abstract Infrared (IR) spectroscopy has been used for routine characterization and identification of clay minerals for many years (Stubican and Roy, 1961; Farmer and Russell, 1964; Farmer, 1974; 1979; Hawthorne, 1988; Russell and Fraser, 1994; Johnston and Wang, 2002; Madejová and Komadel, 2001; Schroeder, 2002). Most applications of this method employ the mid-IR (MIR) region (4000 – 400 cm −1 ) where fundamental stretching (ν) and bending (δ) vibrations of the structural units (e.g., OH and Si-O groups) of the clay minerals occur. In addition to the MIR region, the near-IR (NIR) region (11000 – 4000 cm −1 ) can also provide useful information about clay minerals since the observed bands related to the OH overtones and combination vibrations are sensitively affected by the variations in the clay mineral structure. The popularity of NIR spectroscopy greatly increased in last years due to a pronounced development in the IR instrumentation. High sensitivity of Fourier transform IR spectrometers (e.g., enhanced frequency accuracy, high signal-to noise ratios and high data acquisition speed) allows effective utilization of the diffuse reflectance technique (DRIFT), which is especially appropriate to the NIR region. In contrary to the MIR region, no dilution of the sample is necessary and therefore the IR analysis can be very fast and non-destructive. The history and the development of NIR reflectance spectroscopy is summarized by Clark et al. (1990), including NIR spectra of selected minerals. A NIR database of silicate minerals was established by Hunt and Salisbury (1970) and Hunt et al. (1973) . The assignments of NIR absorption bands of water molecules and lattice-hydroxyl groups of montmorillonites, effect of exchangeable cations, and of layer charge were reported by Cariati et al. (1981, 1983a, 1983b) . Bishop et al. (1994) analyzed NIR spectral features attributed to interlayer water molecules in smectites with different interlayer cations. Post and Noble (1993) found direct linear correlation between the combination band positions and the Al 2 O 3 contents in montmorillonite-beidellite series and muscovite. Bishop et al. (2002a,b) studied in detail the OH vibrations of Febearing dioctahedral smectites and serpentines by absorption features observed in both near- and mid-IR regions. Gates et al. (2002) applied NIR spectroscopy to determine the distribution of Fe in nontronites. Infrared spectroscopy has been extensively used for the studies of smectite structures mainly due to its sensitivity to the distribution of atoms in the octahedral and tetrahedral sheets (e.g., Grauby et al., 1993, 1994 ; Madejová et al., 1994 ; Kloprogge et al., 2000 ; Gates et al., 2002 , Madejová, 2003 ). Smectites consist of layers composed of two tetrahedral sheets linked to an octahedral sheet through sharing of apical oxygens. The tetrahedra contain mainly Si(IV) as the central atom, while the octahedral sites of dioctahedral smectites are occupied mostly by Al(III). The great diversity of smectites occurs owing to isomorphous substitution of the central atoms in tetrahedral (e.g., Al(III) for Si(IV)) and/or octahedral (Fe(III) and Mg(II) for Al(III)) sheets. Non-equivalent substitutions of central atoms generate a negative charge on the layer that is balanced by hydrated exchangeable cations in the interlayers and on the surface of the particles.