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

Concentrations of trace elements in coal derived liquids have been investigated by inductively coupled plasma-mass spectrometry (ICP-MS) and by Mössbauer spectroscopy. Liquefaction extracts prepared from the Argonne Premium Coals and a coal tar pitch have been examined. Microwave digestion in concentrated 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 samples (<265–1474 ppm). Ti, Cr, Mn, Co, Ga, Sb, Cs and Ba were measurable. Concentration distributions of trace elements found in the extracts bore little 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. Mössbauer spectroscopy of the extracts indicated that the high Fe-concentrations corresponded to the presence of organometallic-Fe compounds—and not to pyritic iron. There is evidence suggesting the presence of material derived from iron-storage proteins such as ferritin, but final proof is lacking. Our data suggest that other metallic ions detected in these coal derived liquids may be present in association with the organic material. Concentrations of paramagnetic metal species were 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 13C NMR.