INTERACTIONS BETWEEN CARBOXYL GROUPS AND INORGANIC ELEMENTS IN SPANISH BROWN COALS

Organomineral associations between inorganic elements and carboxyl groups of two Spanish brown coals were characterized. The elements Na, K, Mg and Ca were partly exchanged in carboxylate groups. The concentration of free carboxyl groups was similar for both coals (≈1.9 milliequivalents-gramme H+/g dmmf coal), corresponding to 60% of the carboxylic acid plus ionized carboxylate groups. Study of organic affinities showed that Na and K were predominantly present in mineral matter (especially in clay minerals), while Mg and Ca were mainly associated with organic matter. FT-i.r. spectroscopy provided some additional information on the transformations of organomineral associations after extraction and acid treatment. This technique also showed that extraction with ammonium acetate prevented formation of sulphate and nitrate artefacts during subsequent low-temperature ashing of the residue, confirming the reliability of this two-step procedure for determining mineral matter in low-rank coals. © 1990.