Determination of the Ti speciation in commercial kaolins by Raman spectroscopy

Raman spectra of a selection of kaolins with widely varying TiO 2 contents revealed the presence of anatase in 17 of 18 samples. A significant positive correlation was observed between the intensity of the main anatase Raman band at ~145 cm -1 and the total TiO 2 contents of the kaolins as determined by chemical analysis. No TiO 2 modification other than anatase was detected in any of the samples. The determination of the anatase contents in kaolins by XRD becomes increasingly difficult as the concentration of this mineral decreases below ~0.5%. In contrast, anatase and brookite concentrations an order of magnitude lower can still be readily identified by Raman spectroscopy. The specificity and sensitivity of Raman spectroscopy for these TiO 2 polymorphs, coupled with the simplicity and rapidity of measurement, therefore make this a viable technique for the routine study of these accessory minerals in kaolins.