Characterization of Octahedral Substitutions in Kaolinites Using Near Infrared Spectroscopy

Abstract

Abstract--Fourier transform infrared (FTIR) spectroscopy investigations in the near infrared (N1R) region of synthetic and natural kaolinites with various octahedral substitutions have been carried out in order to elucidate the relationships between the substituted cations and specific features of the NIR spectra. The combination modes of the OH stretching and bending vibrations characterizing Fe(III), Ga(III) and Cr(III) octahedral substitutions are identified in the NIR region at 4466, 4498 and 4474 cm ~, respectively, and the first overtones of the OH stretching vibrations at 7018, 7018 and 6986 cm -J, respectively. As far as we know, the bands of kaolinites containing Ga(III) or Cr(III) have not been reported yet. For both Ga(III) and Cr(HI), the NIR observations explain why the bending vibration bands of A1GaOH and A1CrOH groups are not observed in the middle infrared (MIR) region.

Near-Infrared Spectroscopic Study of Chlorite Minerals

“…These results confirm the hypothesis of Petit et al [34] that IR OH stretching band frequency is dependent on the amount of Fe-Mg substitution. According to Shirozu [8], Fe substitution for Mg in chlorites indirectly weakens the surplus negative charge of the surface oxygens and results in an increase of the O-OH distance and further decreases the frequency of the OH IR stretching band.…”

“…The second type of absorption in this region was located at approximately 850, 757, and 649 cm Figure 6. The weak band near 4525 cm −1 was assigned to the combination of OH stretching and deformation vibrations of Al-OH groups in 2 : 1 layers, and this band was also observed at a similar frequency in kaolinites [34]. Another weak band near 4361 cm −1 was tentatively attributed to an Mg-OH combination band [10].…”

Baseline Studies of the Clay Minerals Society Source Clays: Infrared Methods

“…In addition, reflectance spectra in the near-IR (NIR) region (11,000-4000 cm ~), where overtones and combination vibrations occur, are included. These spectra provide information on structural OH groups and H20 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).…”

Stability of kaolin sand from the Vyšný Petrovec deposit (south Slovakia) in an acid environment

“…Less clear resolution and lower intensity of the 3670 cm -1 band in the VP spectrum than in the spectrum of a well-ordered KGa-1b (Madejová & Komadel 2001) also indicates only medium-ordering of the kaolinite in the VP sample. The absence of the AlFeOH band near 3598 cm -1 implies that iron determined by chemical analysis of VP kaolin is not bound in the kaolinite's octahedral sheets (Petit et al 1999 (Fig. 7c).…”

“…However, a small amount of octahedral iron in natural kaolinites was reported (e.g. Meads & Malden 1975;Mestdagh et al 1980;Petit et al 1999). Particle shape of kaolinite is regular and pseudohexagonal.…”