New kaolinite phases expanded through intercalation with potassium acetate

Full text: Changes in the hydroxyl surfaces of potassium acetate-intercalated kaolinite have been studied over the ambient to predehydroxylation temperature range using a combination of X-ray diffraction and Raman spectroscopy. Upon intercalation, the kaolinite expanded along the c-axis direction to 13.88 Angstroms. Upon heating the intercalation complex over the 50 to 300 deg C range, X-ray diffraction shows the existence of three additional intercalation phases with d-spacings of 9.09, 9.60, and 11.47 Angstroms. The amount of each phase is temperature dependent. These expansions are reversible and upon cooling the intercalation complex returned to its original spacing. The 13.88 Angstroms phase only existed in the presence of water. It is proposed that the expanded kaolinite intercalation phases result from the orientation of the acetate within the intercalation complex. The Raman spectra of the hydroxyl-stretching region (Frost and van der Gaast, 1997) of potassium acetate-intercalated kaolinite has been obtained under an atmosphere of both air and nitrogen using a thermal stage over the 25 to 300 deg C temperature range (Johansson et al., 1998). Raman spectra of the C-C, C=O stretching and O-C-O bending modes show that at least two types of acetate are present in the intercalation complex. These are assigned to two different orientations of the acetate. At 25 deg C, a new band at 3606 cm-1 attributed to the inner surface hydroxyl hydrogen bonded to the acetate ion is observed with a concomitant loss of intensity in the bands attributed to the inner surface hydroxyls (Frost and Kristof, 1997, Frost et al.,1997). Heating the intercalation complex to 50 deg C results in two hydroxyl-stretching frequencies at 3594 and 3604 cm-1. This change in frequencies is ascribed to phase changes of the potassium acetate-intercalated kaolinite. At 100 deg C, the bands shift to 3600 and 3613 cm-1. These shifts in frequencies are assigned to new kaolinite expanded phases. At temperatures from 100 to 300 deg C, bands are observed in similar positions. Upon cooling in air to 25 deg C, the acetate-bonded inner surface hydroxyl stretching frequency shifts back to 3606 cm-1. Upon heating the intercalated kaolinite to 300 deg C, and upon cooling under an atmosphere of nitrogen, the acetate bonded inner surface hydroxyl stretching frequency returns to 3606 cm-1. This shows the phases changes as determined by Raman spectroscopy are reversible. Upon cooling to 150 deg C and subsequently to 25 deg C, two bands are observed at 3611 and 3600 cm-.1. Upon rehydration, the hydroxyl stretching frequency returns to 3606 cm-1