Quantitative mineralogical analysis of coal and associated materials by X-ray diffractometry

PCS-827

Quantitative mineralogical analysis of coal and associated materials by X-ray diffractometry
Ward, Colin R.
Proc., 18th Annual International Pittsburgh Coal Conference 2001 309-326

The mineral matter in coal encompasses any dissolved ions in the pore waters and inorganic elements associated with the organic matter, together with a sometimes quite significant proportion of cryst. mineral particles. Many problems associated with mining, coal preparation and use arise from the nature and relative abundance of particular mineral matter components, providing an increasing need for quant. mineralogical analysis of coals and associated materials for a range of industry applications. The most definitive basis for mineralogical analysis is X-ray diffraction (XRD), which distinguishes minerals from each other on the basis of their at. or crystal structure. Although traditionally regarded as a qual. tool for mineral identification, XRD has benefitted from recent developments in computer processing that enable it also to be used for quant. determination of mineral percentages. An example is the SIROQUANT technique for quant. XRD evaluation, based on Rietveld methods of diffraction pattern analysis. The SIROQUANT technique involves interactive adjustment of the diffraction patterns of individual minerals to allow for crystallog. variations, and combines the adjusted patterns to match the observed XRD profile of the sample under analysis and evaluate the percentages of the different minerals present. This paper discusses the use of SIROQUANT for determining the mineral percentages in a range of coals and associated rocks, including the Argonne Premium Coals reference set. The materials investigated include raw coal samples, as well as low-temperature ashes isolated from the coals by radio frequency activated oxygen-plasma techniques. Some higher-temperature ashes, prepared by heating the coals in air at 370 C, have also been analyzed. The chemical compn. calculated from the mineral percentages determined by SIROQUANT is typically very close to the actual chemical compn. of the same materials determined by direct chemical analysis, confirming that the quant. XRD results are consistent with other indicators of mineral matter constitution. Supplementary data have also been obtained in other studies from detailed evaluation of the clay minerals, using special oriented-aggregate XRD techniques. Clay mineral proportions indicated by SIROQUANT from powder diffraction data in these studies are similar to those estimated within the clay fraction from oriented-aggregate evaluations. The availability of a more quant. basis for mineralogical analysis provides a range of opportunities to relate mineral matter characteristics to other coal properties. These include studies of particular trace elements, as well as materials handling and related characteristics. Quant. analysis also provides an opportunity to establish links between the mineral assemblages in coals and the mineralogy of slags and other furnace deposits, and to evaluate the behavior, of mineral matter more fully in a range of coal utilization processes.

1. Upper Freeport,PA (UF)
2. Wyodak-Anderson, WY (WY)
3. Illinois #6 (IL)
4. Pittsburgh #8 (PIT)
5. Pocahontas #3 (POC)
6. Blind Canyon,UT (UT)
7. Lewiston-Stockton, WV (WV)
8. Beulah-Zap, ND (ND)