The distribution and origin of trace elements in a UK coal; the importanceof pyrite

Coal samples were obtained from a multigravity separator at Harworth (UK) c oal-preparation plant. The minerals identified by X-ray diffraction in low- temperature ashes include kaolinite, illite, mixed-layer illite-smectite, c hlorite, quartz, pyrite, apatite and gypsum. The latter is an artefact of t he ashing procedure. Based on X-ray diffraction and major element analyses the coal samples show a preferential separation of quartz and pyrite. Sampl es were analysed for trace elements using energy dispersive, polarised XRF and data obtained for 25 trace elements with detection levels of similar to 1 ppm for most elements and sub-ppm for some. One group of trace elements shows highly significant correlations within the group and with the pyritic S%. The concentrations (in ppmw) of these elements in pyrite were determin ed, per 1 wt% pyritic S, as: Mo 2., Se 0.6, Ni 8.2, As 21, Pb 6.1, Sb 0.4, Cu 13.8 and Zn 8.8. There are other sources for these elements in the coal, particularly for Ni, Cu and Zn, but pyrite is the main location. The conce ntration levels determined for pyrite may be applicable to pyrite in other coals because of a common process of enrichment from a seawater source. Ano ther group of elements, consisting of Rb, V, Cr, Ga, Sr, Y, Zr, Nb, Sn, Ba, La, Ce and Th is thought to be contained within the detrital minerals. The only member of this group with a significant nondetrital origin is V, whic h is probably contained within the organic matter and in a low ash coal thi s would appear to be the major source. Germanium and Br are the two element s which have a dominant organic association. (C) 1999 Elsevier Science Ltd. All rights reserved.