Microwave digestion with HNO3/H2O2 mixture at high temperatures for determination of trace elements in coal by ICP-OES and ICP-MS

Abstract

The purpose of this paper is to validate the microwave digestion method with a HNO3/H2O2 mixture for determination of 18 trace elements (Li, Be, V, Cr, Mn, Co, Ni, Cu, Zn, Ga, As, Se, Rb, Sr, Cd, Cs, Ba, and Pb) in coal by inductively coupled plasma optical emission spectrometry and inductively coupled plasma mass spectrometry. The digestion with a HNO3/H2O2/minute HF mixture was conducted for comparison, and the results were evaluated with reference to three standard coals (SRM1632c, BCR180, and SARM19). It was found that the addition of HF was not required to extract quantitatively the above trace elements in all three coals with the exception of Rb in SARM19 coal by elevating the digestion temperature to 220 °C and pressure to 2 MPa. Through this rigorous digestion, the organic matrices and clay minerals in coal were extensively decomposed even without HF. However, some trace elements such as V, Cr, Ni, Ga, Sr, and Ba in SARM19 coal were not quantitatively extracted under a milder condition (180 °C and 0.9 MPa), probably because these trace elements partially remained in the organic matrix and clay residues.