A Fourier transform infrared spectroscopic study of Mg-rich, Mg-poor and acid leached palygorskites

The FTIR spectra of pure magnesium-rich (Mg-rich) and magnesium-poor (Mg-poor) palygorskites, before and after short-term (< 7 h) and long-term (360 h) acid leaching are presented here. Comparison of decomposition spectra of Mg-rich and Mg-poor palygorskites clearly shows that the absorption peaks related to pairs of octahedral cation differ depending on the octahedral site occupancy. Short-term acid leaching of palygorskites results in significant changes to FTIR absorption bands near 1200 and 790 cm(-1). As the acid attack progresses, the band at 1200 cm(-1) shifts to lower wavenumbers, whilst the band at 790 cm(-1), which here is assigned to Si-U-O-Si-D symmetrical stretching vibration, shifts to higher wavelengths. Longer-term leaching of palygorskites results in the disappearance of 900-1200 cm(-1) absorption bands, showing that the palygorskite has largely decomposed to amorphous silica. Assignments of several other bands have been made as follows: several vibrations relate to OH, i.e. 847 cm(-1), hygroscopic water (1635 cm(-1)), Si-O vibrations 1100, 611-621, 470-481 cm(-1), etc. appear in the FTIR spectra of 360 h acid leached palygorskite. Three bands near 1100, 611-621 and 470-481 cm(-1) relate to Si-O vibration of an ideal hexagonal (Si2O5). sheet. (c) 2006 Elsevier B.V. All rights reserved.