The determination of minor and trace element associations in coal using a sequential microwave digestion procedure

Abstract

A sequential extraction procedure, using acid digestion in a CEM MDS-81D® microwave system, is reported for the investigation of trace and minor element associations in coal in (1) mineral phases other than pyrite, (2) pyrite and (3) the organic matrix. The concentrations of sulphate, pyrite and organic sulphur can also be determined by this method. The extract solutions from each stage are rapidly analysed by ICP-AES. The association of major, minor and trace elements with mineral and organic phases is suggested for a suite of certified reference coal samples. In stage 1, a significant percentage of the total Ba, Co, Cr, Cu, Mn, Ni, Pb and Sr was extracted suggesting an association with silicate, carbonate, sulphate and phosphate minerals for these elements. In stage 2, a proportion of the Cu, Mn, Ni, Pb and Zn was dissolved implying the occurrence of these elements in pyrite. An association with the organic matrix is suggested for Cr and also for Ba and Sr in lower rank coals.