Analysis of Kaolinite/Chrysotile Mixtures by Ashing and X-Ray Diffraction
Jennifer R. Verkouteren, Eric S. Windsor, Joseph M. Conny, R L. Perkins, J T. Ennis
A simple ashing procedure is described that converts kaolinite to amorphous metakaolinite while retaining the diffraction intensity of chrysotile. This ashing procedure removes the XRD pattern overlap between kaolinite and chrysotile that can interfere with the analysis of even high concentrations of chrysotile (>0.10 mass fraction). Samples are ashed at 460 degrees C in a muffle furnace for 40 hours to completely convert kaolinite to metakaolinite. The complete conversion of 1 g of kaolinite under these conditions was determined for two standard kaolinite samples from Georgia, KGa-1 and KGa-2. Two of the most common types of commercial chrysotile, long-fiber Canadian and short-fiber Californian chrysotile, are demonstrated to retain diffraction intensity after ashing at 460 degrees C. Both chrysotile samples have the same integrated intensity for the (002) reflection prior to ashing, although the peak breadths for the two samples are quite different. Ashing at temperatures above 460 degrees C reduces the diffraction intensities of both chrysotile samples by 15 %, and broadens the peaks by approximately 3 %. Using the prescribed ashing procedure and x-ray diffraction with an internal standard, two kaolinite-bearing building materials containing chrysotile near 0.01 mass fraction were analyzed. The ashing procedure has additional advantages in reducing some samples to powders and removing volatile components, thereby eliminating some sample preparation procedures and concentrating any chrysotile present in the sample. The removal of volatile components improves the sensitivity of XRD analysis to concentrations below 0.01 mf chrysotile.