MODES OF OCCURRENCE OF TRACE-ELEMENTS IN COAL FROM XAFS SPECTROSCOPY

Experimental aspects of X-ray absorption fine structure (XAFS) spectro scopy are described for determining the mode of occurrence of selected trace elements in coal. For elements between calcium and molybdenum i n the periodic table, information relating to the mode of occurrence c an be deduced from the XAFS spectrum provided the element's concentrat ion exceeds about 5 ppm. This spectroscopic method of determining elem ental modes of occurrence complements electron microscope or microprob e methods because it provides information on element forms dispersed i n the organic fraction of coal as well as on the mineralogical forms o f the element. XAFS spectra for the lithophile elements, Ti, V, Cr and possibly Mn, indicate that these elements can be associated with both the minerals (principally illite) and the macerals in coals of rank u p to high volatile bituminous. XAFS data also confirm that Mn, Zn, As and Br, can be largely organically associated in certain coals. XAFS s pectra for As, and to a lesser extent, Se show that these elements wil l oxidize over time, once the coal has been exposed to air.