Techniques for the differentiation of carbon types present in lignite-richmine soils

The objective of this study was to assess high energy UV photo-oxidation, C -13 CP/MAS NMR spectroscopy and C-14 activity measurements for their suitab ility in differentiating carbon derived from plant material and that derive d from lignite. The conceptual approach included analysis of bulk soil samp les and physical fractions of lignite-rich mine soils. Additionally, the <5 3 mu m fraction of selected samples was subjected to 2 hours of high-energy UV photo-oxidation. Quantification of the lignite carbon content by C-14 a ctivity measurements showed that a mixture of lignite and recently formed o rganic matter occurs in the bulk surface soil horizon as well as a number o f particle size and density fractions. Using C-13 CP/MAS NMR spectroscopy, carbon species, characteristic for lignite- and plant-derived organic matte r can be identified. Both methods yield corresponding results. It was also shown that lignite-derived carbon is more resistant to the high-energy UV p hoto-oxidation treatment than carbon derived from recent plant material. Th is method provides qualitative indications of lignite contribution to soils . (C) 2000 Elsevier Science Ltd. All rights reserved.