The organic association of elements in coals

Abstract Various aspects of the organic association of trace elements in coals are reviewed. For estimating organic affinity, reference is made to float-sink methods, the relationship between trace-element content and ash yield, and mild extraction. Carboxylic acid, phenolic hydroxyl, mercapto and imino groups are discussed in relation to organic bonding of trace elements in coal. Information is given for individual trace elements that may be predominantly organically bound. It is concluded that there is a lack of direct evidence for the organic association of most trace elements in coals, except for some law-ash, low-rank coals.