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Coal fly ash contains several trace elements some of which are toxic such as As, Cr, Pb, etc. Coal ash also contains relatively high amounts of rare earth elements whose recovery from coal ash could be an alternate source for their supply. Although uranium and thorium are less chemically toxic than other constituent elements such as arsenic, questions have been raised concerning the possible risk from radiation. Hence, the concentration levels of all of these trace toxic elements in fly ash samples have to be assessed to determine whether the ash is hazardous or not, and also to decide the place and method of its disposal or reutilization. In this study, multielemental analysis of some coal ash samples originating from two thermal power plants in southern India has been carried out, employing inductively coupled plasma atomic emission spectrometry (ICP-AES) and inductively coupled plasma mass spectrometry (ICP-MS), with the focus on some trace toxic elements. The methods employed were validated by analayzing international certified fly ash reference materials. The concentrations of trace-toxic elements in the samples analyzed were: 20-82 µg/g for As, 45-281 µg/g for Cr, 31-607 µg/g for Ba, 21-865 µg/g for Sr, 8-39 µg/g for Ge, <5-80 µg/g for Ga, <5-100 µg/g for Cu, 19-50 µg/g for Co, 58-258 µg/g for Ni, 8-73 µg/g for Pb, 44-260 µg/g for Zn, 0.6-8.6 µg/g for U, 1-30 µg/g for Th, 6-196 µg/g for La, 14-528 µg/g for Ce, 5-196 µg/g for Y. These results were compared with trace-toxic element concentrations in coal ash samples as reported in the literature.

The analytical results obtained by both methods were found to compare well with each other as well as with the results obtained by ICP-OES in the case of REEs, uranium, and thorium. However, in the case of zirconium, quantitative recoveries were obtained only with the fluoride fusion method. Though international monazite reference materials are available, certified or even probable values are not available for all the constituent elements. A certified monazite reference material, BGS: IGS-36 (British Geological Survey/Institute of Geological Sciences, U.K) was analyzed, and the results obtained are presented in this paper. The analytical results by both methods were found to compare well with each other and with the accepted values reported in literature for IGS-36. The %RSD for all the estimated elements varied from 1.0 to 4.0% at mg g-1 levels and from 5.0 to 15.0% at µg g-1 levels of concentration.

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