Aspects of structural features in lignite and lignite humic acids

Structural features of a South Moravian lignite and its humic acid (HA) fraction were studied by means of UV-vis, H-1 and solid-state C-13 NMR, and FT-IR spectroscopy in addition to basic elemental analyses. The structural differences between the original lignite and its HA-type fraction were relatively minor, and their unambiguous differentiation into distinct categories was possible only by statistical methods. The tested model functions speak strongly for the importance of choosing enough sensitive and meaningful structural parameters which most likely reflect the character or type-rank of the coal-like carbon in question. The results verified that certain aliphatic compounds have their special tasks in the complicated structural network of lignite HA material, and powerful aprotic solvents are needed to obtain a fully dissolved HA solution. Despite some organic material was lost during different effective washing purification operations, the purified lignite HA was typified without significant loss of structural information on the original HA fraction. FT-IR experiments correlated well with those obtained by C-13 NMR. From environmental points' of view, some water soluble organic trace components released from the original lignite material may be potential troublemakers within the area surrounding the deposit. (C) 2006 Elsevier B.V. All rights reserved.