Quantitative analysis of anatase in Georgia kaolins using Raman spectroscopy

摘要

Raman spectroscopy of Georgia kaolins ubiquitously show a strong E_g frequency near 144 cm~(-1). Analysis of the band intensity shows that under specific source, sample, and optical conditions, peak area measurements are predictable and reproducible. Using standard additions, successful quantitative techniques have been developed that allow analysis of 25% solids water slurries, which achieve anatase detection limits down to 0.3% with a standard error of +-0.1%. Anatase was also studied with X-ray powder diffraction to examine the extent of crystal chemical variation. The a lattice dimensions of anatase from Georgia kaolins range from 0.3786 to 0.3796 nm. The mean coherent scattering length in the [100] direction range from 80 to 160 nm. Given the range of anatase particle sizes previously observed in Georgia kaolins (8000-150,000 run), these parameters indicate an average defect density of 100 domains per crystal and structural formulae that range from Fe_(0.03)Ti_(0.97) O_(1.97)(OH)_(0.03) to Fe_(0.06)Ti_(0.93)O_(1.93)(OH)_(0.06). Quantitative estimates of anatase abundance using Raman require careful attention to background fluorescence effects due to the presence of hematite, goethite, and organic matter. Background fluorescence intensity in the regions of 400 and 600 cm~(-1) correlate with known additions of hematite and goethite, respectively. The removal of organic matter from gray clays by H_2O_2 treatment significantly reduced background fluorescence. The small variations in anatase crystal chemistry do not appear to have any first-order effects on Raman intensity of the 144 cm~(-1) band. The comparison of total TiO_2 using X-ray fluorescence techniques with anatase content reveals that, in many instances, there is a significant non-anatase TiO_2 component present in Georgia kaolins. The discrimination of Ti-phases has the potential to provide new insights into strategies for mineral separation techniques, kaolin reserve estimates, and understanding of the geologic history of the Georgia kaolin deposits.