Bentonite Mineralogy Part 1: Methods of Investigation - Posiva

%T
7.2 Fourier transform infrared spectroscopy {FTIR)
45
The smectite mineral in all studied bentonite samples is montmorillonite (or beidellite ).
The OH-stretching bands in the 3500-3600 cm- region of their infrared spectra are
broad and consist of several umesolved components. Maximum absorption occurs at
3636 cm- 1 in the Wyoming samples (Fig. 7-9), at 3621-3626 cm- 1 in the Kutch samples,
at 3625-3632 cm- 1 in the Milos samples (Appendix 4) and at 3621 cm- 1 in the Czech
samples (Fig. 7-10). The AIAIOH stretching band typically occurs at 3620-3630 cm- 1 ,
the AIMgOH stretching band at 3687 cm- 1 and the A1Fe 3 +0H band at 3597 cm- 1
(Farmer, 1974). The frequency of maximum absorption thus indicates that the smectites
are Al-rich. The broadness of the band is due to the contribution of Mg and Fe in
octahedral sheets and might also indicate, that the smectite structure is poorly ordered.
In nontronites maximum absorption occurs at frequency ea 3560 cm- 1 (Farmer, 1974).
Nontronite was not identified in any of the studied samples.
Wyoming
BH-200
MX-80
4000,0 3000 2000 1500 450,0
cm-1
Figure 7-9. FTIR spectra of the Wyoming bentonites, fine fraction.