BASELINE STUDIES OF THE CLAY MINERALS SOCIETY SOURCE CLAYS: INFRARED METHODS

Abstract

Infrared (IR) spectroscopy has a long and successful history as an analytical technique and is used extensively (McKelvy et al., 1996; Stuart, 1996). It is mainly a complementary method to X-ray diffraction (XRD) and other methods used to investigate clays and clay minerals. It is an economical, rapid and common technique because a spectrum can be obtained in a few minutes and the instruments are sufficiently inexpensive as to be available in many laboratories. An IR spectrum can serve as a fingerprint for mineral identification, but it can also give unique information about the mineral structure, including the family of minerals to which the specimen belongs and the degree of regularity within the structure, the nature of isomorphic substituents, the distinction of molecular water from constitutional hydroxyl, and the presence of both crystalline and non-crystalline impurities (Farmer, 1979). The interpretation of the absorption spectra of the Source Clays in the middle-IR (MIR) region (4000–400 cm−1) given here follows those of Farmer and Russell (1964), Farmer (1974a, 1979) and Russell and Fraser (1994). In addition, reflectance spectra in the near-IR (NIR) region (11,000–4000 cm−1), where overtones and combination vibrations occur, are included. These spectra provide information on structural OH groups and H2O in clay minerals (Bishop et al., 1994; Frost and Johansson, 1998; Petit et al., 1999a) which may not be clearly observed in the MIR spectra. Small changes in stretching and bending band positions are additive in the combination bands, thereby making them more readily differentiated (Post and Noble, 1993). Dispersive IR spectrometers are slowly being replaced by quicker and more sensitive Fourier transform (FT) instruments (Rintoul et al., 1998). The greater sensitivity of the FTIR spectrometers is related to the continuous detection of the entire transmitted energy …