QUANTITATIVE INORGANIC PROFILING OF COAL SEAMS USING CORE-SCANNING XRF TECHNIQUES

Detailed quantitative profiles have been produced to show the abundance and distribution of inorganic elements in coal cores using an Itrax core scanner (Cox Analytical, Sweden). Such an approach allows non-destructive evaluation of the mineral, sulphur and ash profile in a coal seam, identifying horizons at which particular inorganic components may be concentrated, evaluating relationships between different elements in the coal, and guiding sampling for conventional analysis programs. In conjunction with X-radiography, carried out as part of the scanning process, the results may also assist in understanding the mode of occurrence, formation and distribution of the different minerals within the seam, and in the design of facilities for optimum beneficiation of the mined coal products.

Calibration curves were prepared for key major elements (Al, Si, P, S, K, Ca, Ti and Fe) based on pressed pellets of independently-analysed reference coals. The calibrated XRF data were used to produce a set of quantitative element and element-oxide profiles, and these were plotted alongside the relevant X-radiograph and optical image to provide an integrated basis for assessing the variations in inorganic element characteristics through the core. The results were also compared to conventionally-determined chemical and mineralogical data for a representative core, to confirm the validity of the quantifications developed.

Although Na and Mg were below detection limits and could not be measured, the sum of the other major elements, expressed as oxides, was found to be approximately the same as the ash yield of the coal. It was also inversely related to the level of Compton backscatter from the coal measured by the core scanner, allowing correlation with the parameter commonly used in down-hole geophysical (density) logging as an indicator of coal quality and ash yield.

The capacity of hand-held portable XRF analyzers to provide similar data on coal cores is also being investigated, including separate calibration tests and comparative studies against the laboratory core-scanning system.