Trace elements in coal derived liquids: analysis by ICP-MS and Mossbauer spectroscopy

Concentrations of trace elements in coal derived Liquids have been investig ated by inductively coupled plasma-mass spectrometry (ICPMS) and by Mossbau er spectroscopy. Liquefaction extracts prepared from the Argonne Premium Co als and a coal tar pitch have been examined. Microwave digestion in concent rated nitric acid has been shown as a suitable method for determining trace element concentrations in coal derived liquids by ICP-MS-for sample sizes as small as 3-20 mg. High concentrations of Fe were found for all extract s amples (<265-1474 ppm). Ti, Cr, Mn, Co, Ga, Sb, Cs and Pa were measurable. Concentration distributions of trace elements found in the extracts bore li ttle relation to the corresponding distributions in the original coals. The proportions of individual trace elements present in the original coals and found in the extracts, varied widely. Mossbauer spectroscopy of the extrac ts indicated that the high Fe-concentrations corresponded to the presence o f organometallic-Fe compounds-and not to pyritic iron. There is evidence su ggesting the presence of material derived from iron-storage proteins such a s ferritin, but final proof is lacking. Our data suggest that other metalli c ions detected in these coal derived liquids may be present in association with the organic material. Concentrations of paramagnetic metal species we re found to be of the same order of magnitude as ESR spin-densities already found in coal liquids. Both types of paramagnetic species are suspected of causing loss of signal in solid state C-13 NMR. (C) 1999 Elsevier Science Ltd. All rights reserved.