Modes of Occurrence of Trace Elements in Coal from Xafs Spectroscopy

INTRODUCTION I t is well known that elements exist in coal in a variety of different modes of occurrence [1,2]. Such modes can vary from the element being totally dispersed in the macerals (e.g. organic sulfur, carboxyl-bound Ca in lignite) to discrete mineral occurrences (e.g. pyrite, FeS,, quartz, SiO,, etc.). Recently, we showed that X-ray absorption fine structure (XAFS) spectroscopy is capable of recording spectra from elements present in coal a t concentration levels as low as 5 ppm [31. Such information, obtained directly with a minimum of sample preparation, is proving to be invaluable for the elucidation of a trace element's mode of occurrence. In the previous work, we used XAFS spectroscopy to identify the principal modes of occurrence of arsenic and chromium in various coals. Here, we present more recent XAFS spectroscopic observations on these and other trace elements in coal and take the opportunity to discuss the ramifications of such XAFS studies for geochemical investigation of trace elements in coal.