Determination of element affinities by density fractionation of bulk coal samples

A review has been made of the various methods of determining major and trac e element affinities for different phases, both mineral and organic in coal s, citing their various strengths and weaknesses. These include mathematica l deconvolution of chemical analyses, direct microanalysis, sequential extr action procedures and density fractionation. A new methodology combining density fractionation with mathematical deconvo lution of chemical analyses of whole coals and their density fractions has been evaluated. These coals formed part of the IEA-Coal Research project on the Modes of Occurrence of Trace Elements in Coal. Results were compared t o a previously reported sequential extraction methodology and showed good a greement for most elements. For particular elements (Be, Mo, Cu, Se and REE s) in specific coals where disagreement was found, it was concluded that th e occurrence of rare trace element bearing phases may account for the discr epancy, and modifications to the general procedure must be made to account for these. (C) 2000 Elsevier Science Ltd. All rights reserved.