Speciation of Selected HAPs Elements in Coal Ash

摘要

XAFS spectroscopy is a powerful method for determining the oxidation state and possible forms of occurrence of trace and minor elements in ash products obtained from coal combustion and hence for supplying answers regarding the environmental and health hazards posed by HAPs elements in coal and ash. The technique is direct, nondestructive, and has a sensitivity of 10 ppm for certain elements. For elements such as chromium and arsenic, it is possible to determine the relative amounts of the main oxidation states with a precision of about ±5%. Among the elements discussed here, in all cases, the most toxic form, e.g. Cr(VI), As(III), Ni subsulfides, is either absent or relatively subordinate in coal combustion products. However, in the case of both Cr(VT) or As(III), it would appear that it would not take a great change in combustion conditions to promote significant formation of either of these highly toxic forms in ash.