The association of major, minor and trace inorganic elements with lignites. II. Minerals, and major and minor element profiles, in four seams

Abstract

Abstract Inorganic elements in lignites may be present in carboxylate salts and organic coordination complexes as well as in discrete mineral phases. Moreover, organic matter can alter mineral phases in peats. The objectives of this study are to investigate how a number of important elements are held in some typical lignites and hence to document organic inorganic interactions of various kinds. Accordingly, detailed profiles of the distribution of 10 major and minor elements through four lignite seams have been made, including roof and floor rocks and any mineral partings. Elements extractable by 1.0 N ammonium acetate and by 1.0 N HCl and in the insoluble residue have been analyzed by plasma arc emission and atomic absorption spectrometry. Mineral phases were analyzed by x-ray diffraction and infrared spectrometry. Substanial proportions (40–90%) of the Ca, Mg, Sr, Ba, Na and Mn were extractable from the organic zones, but not the inorganic, by ammonium acetate, and were inferred to have been present in the organic matter as carboxylate salts. Much of the K and some Mg were present in clay minerals, but K-containing clays were depleted in the coal layers relative to roof and floor, probably because organic acids in the peat had leached the K out of illite, thus altering the clays. Part of the Mn was in the organic matter either complexed or dispersed as acid-soluble mineral (e.g. MnS, MnCO3). Acid-soluble Al and Ti were found to be quite abundant in the organic layers but not in the roof and floor; they probably are complexed with the organic matter. The principal conclusion is that the organic matter in peat and lignites has a profound influence, in many ways, on the suite of inorganic materials with which it becomes associated.