FT-Raman spectroscopy and SEM of gibbsite, bayerite, boehmite and diaspore in relation to the characterization of bauxite

Gibbsite, bayerite, boehmite and diaspore were investigated using FT-Raman spectroscopy in conjunction with scanning electron microscopy (SEM) in order to provide information for the characterization of bauxite. The Raman spectrum of gibbsite shows four strong, sharp bands at 3617, 3522, 3433 and 3364 cm(-1) and the spectrum of bayerite shows seven bands at 3664, 3652, 3552, 3542, 3450, 3438, and 3420 cm(-1) in the hydroxyl stretching region. Four broad and weak bands are observed at 3371, 3220, 3085 and 2989 cm(-1) for boehmite, and five broad bands are observed at 3445, 3363, 3226, 3119 and 2936 cm(-1) for diaspore in the hydroxyl stretching region. The hydroxyl stretching bands are related to the surface structure of these minerals. The Raman spectra of bayerite, gibbsite and diaspore are complex while the Raman spectrum of boehmite only shows three major bands in the hydroxyl deformation and water bending, and low frequency regions. These bands are assigned to hydroxyl deformation and translational, and Al-O modes of the alumina phases. The present results in relation to the characterization of bauxite are interpreted.