NONDESTRUCTIVE DETERMINATION OF TRACE-ELEMENT SPECIATION IN COAL AND COAL ASH BY XAFS SPECTROSCOPY

The environmental impact of specific trace element species in coal utilization and waste disposal depends not only on the abundance but also on the form(s) of occurrence of the element present in coal and coal ash. While there are a number of analytical methods for determining the abundance of trace elements in coal and ash, there are very few methods available for determining the form of occurrence (speciation) of a trace element in such materials at abundances as low as 10 ppm. In this report, the potential of XAFS spectroscopy for trace element speciation is demonstrated by means of measurements on two environmentally important trace elements, arsenic and chromium, in coal and ash. Results indicate that arsenic in coal is most commonly present as arsenical pyrite (in which form it may readily oxidize to arsenate, AsO43-, even under ambient storage conditions), and that arsenic is present as arsenate in ash and slag. Conversely, chromium is present as Cr3+ in coal and remains in that oxidation state in ash and slag.