Zielinski and Finkelman reported in 1997 that coal is largely composed of organic matter, but it is the inorganic matter in coal, minerals and trace elements, that have been cited as possible causes of health, environmental, and technological problems associated with the use of coal. Some trace elements in coal are naturally radioactive. These radioactive elements include uranium, thorium, and their numerous decay products, including radium and radon. Although these elements are less chemically toxic than other coal constituents such as As, Se, Hg, and REEs, questions have been raised concerning possible risk from radiation. In order to accurately address these questions and to predict the mobility of radioactive elements during the coal fuel-cycle, it is important to determine the concentration, distribution, and form of radioactive elements in coal and fly ash. Radioactive elements in coal and fly ash should not be sources of alarm.
The vast majority of coal and the majority of fly ash are not significantly enriched in radioactive elements, or in associated radioactivity, compared to common soils and rocks. This observation provides a useful geologic perspective for addressing some of the societal concerns regarding possible radiation and radon hazard. The location and form of radioactive elements in fly ash determine the availability of elements for leaching during ash utilization or disposal. Existing measurements of uranium distribution in fly ash particles indicate a uniform distribution of uranium throughout the glassy particles. The apparent absence of abundant, surfacebound, and relatively available uranium, suggest that the rate of release of uranium is dominantly controlled by the relatively slow dissolution of host ash particles. Previous studies of dissolved radioelements in the environment, and existing knowledge of the chemical properties of uranium and radium can be used to predict the most important chemical controls, such as pH, etc.
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