'Rocky Mountain leather', sepiolite and attapulgite - an infrared emission spectroscopic study

The dehydration and dehydroxylation of the clay minerals attapulgite, sepiolite and 'Rocky Mountain leather' have been analysed by infrared emission spectroscopy. The 'Rocky Mountain leather' and attapulgite are shown to be identical. Infrared emission spectroscopy of the thermal degradation over the temperature range of 100 to 700 degrees C has been used to characterise the thermal decomposition of both sepiolite and attapulgite. Attapulgite is characterised by two bands in the water bending region at 1595 and 1635 cm(-1), attributed to coordinated zeolitic and adsorbed water, respectively. A band was also observed in this region at 1425 cm(-1). The hydroxyl stretching region of attapulgite is complex with bands observed at 3731, 3710, 3670, 3645, 3610, 3590, and 3532 cm(-1). Bands in this region are assigned to either hydroxyl stretching vibrations of water, occurring below 3600 cm(-1) or to hydroxyl bands associated with coordinated hydroxyl groups, occurring above 3600 cm(-1). The first two bands at 3731 and 3710 cm(-1) are attributed to SiOH stretching vibrations. The next five bands are attributed to hydroxyls associated with the magnesium. Another two hydroxyl stretching bands at similar to 3385 and 3315 cm(-1) are attributed to the two types of water molecules, the zeolitic water and coordinated water. The infrared emission spectra of sepiolite were found to be considerably different. Four hydroxyl-stretching frequencies were observed at 3735, 3722, 3688, and 3670 cm(-1). This difference is attributed to the basic difference in the two minerals. The dehydration of attapulgite and sepiolite is followed by the loss of intensity of the water hydroxyl bands. Dehydroxylation is followed by the decrease in intensity in the bands between 3731 and 3532 cm(-1). Dehydration was complete by 300 degrees C and partial dehydroxylation by 700 degrees C. The Si-OH hydroxyl groups remained until similar to 970 degrees C. (C) 1998 Elsevier Science B.V. All rights reserved.