The characterisation of density separated coal fractions using FTIR and petrographic analysis

Density separated coal fractions of Point of Ayr coal, UK, have been analysed by use of infrared spectroscopy and petrographic techniques. Separations were carried out on a -38+20 mu m size fraction in a heavy liquid medium using a float-sink procedure. Petrographic analysis consisted of automated image analysis and manual point counting to identify maceral content. Infrared analysis was carried out by recording the infrared spectra using the diffuse reflectance technique. Area measurements of the aromatic (A(Ar)) and aliphatic (A(Al)) CH stretch absorptions together with area ratios of these absorptions (A(Ar)/A(Al)) were determined for the density fractions and the feed coal. A correlation between the area ratios and point count data was formulated by the use of regression analysis (R-2 = 0.97), together with a correlation between the area ratios and reflectance histograms from image analysis (R-2 = 0.98). The results of the study indicate that changes in the infrared spectrum may be directly related to maceral composition.