Optimised method of coal digestion for trace metal determination by atomicabsorption spectroscopy

Understanding the transport of trace elements through a coal-fired power pl ant requires reliable analytical methods for these elements in all the ingo ing and outgoing mass streams. Coal and different kinds of ashes comprise t he most abundant mass streams in such a plant. As a continuation of our pre vious work, we have optimised a digestion method for the AAS determination of heavy metals in coal samples. It has become evident that complete dissol ution of metals in coal samples and accurate results in subsequent analysis can be obtained by means of applying pressurised digestion under microwave heating. The combination of HNO3 (conc.) and HF (conc.) in the volume rati o of 50:1 attacked the sample well enough, and good recoveries for all the metals studied were obtained. Surprisingly good results were obtained also when HNO3 alone was used as the digestion acid.