An integrated approach based on oxidative pyrolysis and microwave-assisted digestion for the multi-elemental analysis of coal samples by ICP-based techniques

Abstract

Complete dissolution of the coal sample has been achieved using an integrated approach based on oxidative pyrolysis (OP) and microwave-assisted digestion (MWD) for the quantitative determination of major to ultra-trace elements by inductively coupled plasma (ICP)-based techniques. The coal samples were initially pyrolysed by heating to similar to 500 degrees C in the presence of an oxygen stream. Subsequently MWD was applied to the pyrolysed coal residue with an acid mixture of 8 mL of 20%HNO3 + 5%HF + 5%H2O2 or 20%HNO3 + 0.4%NH4HF2 + 5%H2O2. Analysis was carried out by ICP-MS (Be, V, Cr, Mn, Co, Ni, Cu, Zn, As, Rb, Sr, Mo, Cd, Sb, Cs, Ba, W, Tl, Pb, Th, U and REEs) and ICP-OES (Na, K, Ca, Mg, Fe, Al, Sc, Ti). Critical experimental parameters related to OP and MWD were optimized through the analysis of two standard reference materials (SRMs) NIST-1632d and NIST-2685b. Studies with NH4HF2 have demonstrated that it can be used as a replacement to the highly toxic HF for achieving quantitative recovery (> 95%) of most of the elements studied here. The optimized method was subsequently applied to Indian coal samples collected from different coal mines. (C) 2015 Elsevier Ltd. All rights reserved.