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 SiU–O–SiD 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)n sheet.