The Dehydroxylation of the Kaolinite Clay Minerals using Infrared Emission Spectroscopy

Ray L. Frost1 and Anthony M. Vassallo2
1 Centre for Instrumental and Developmental Chemistry, Queensland University of Technology, 2 George Street, GPO Box 2434, Brisbane Queensland 4001, Australia
2 CSIRO Division of Coal and Energy Technology, PO Box 136, North Ryde NSW 2113, Australia

Abstract: The dehydroxylation of a series of the kaolinite clay minerals, kaolinite, halloysite and dickite, has been investigated by Fourier transform in situ infrared emission spectroscopy over a temperature range of 100 to 800°C at both 50 and 5° intervals. Excellent correspondence was obtained between the high temperature emission spectra and FTIR absorption spectra of the quenched clay mineral phases. The major advantage of the technique lies in the ability to obtain vibrational spectroscopic information in situ at the elevated temperature. Dehydroxylation at a number of temperatures was determined by the loss of intensity of hydroxyl bands as indicated by intensity changes of the 3550 cm−1 to 3750 cm−1 emission spectra. As with all clay minerals, kaolinite clay mineral dehydroxylation is structure dependent. No clay phase changes occur until after dehydroxylation takes place. The kaolinite clay mineral loses the inner sheet and inner hydroxyl groups simultaneously, whereas dickite and halloysites are shown to lose the outer hydroxyls, as evidenced by the intensity loss of the ∼3684 cm−1 peak, before the inner hydroxyl groups as determined by the intensity loss of the 3620 cm−1 peak. Evidence for a high temperature stable hydroxyl band at 3730 cm−1 for dickite and halloysite was obtained. This band is attributed to the formation of a silanol group formed during the dehydroxylation process. It is proposed that the dehydroxylation process for kaolinite takes place homogenously and involves 2 mechanisms. The dehydroxylation of dickite and halloysite takes place in steps, with the first hydroxyl loss taking place homogenously and the second inhomogenously.

Key Words: Dehydroxylation • Dickite • Emission • Halloysite • Hydroxyl • Infrared • Kandite • Kaolinite • Mechanism of dehydroxylation

Clays and Clay Minerals; October 1996 v. 44; no. 5; p. 635-651; DOI: 10.1346/CCMN.1996.0440506
© 1996, The Clay Minerals Society
Clay Minerals Society (www.clays.org)