Spectral characterization and comparison of humic acids isolated from some European lignites

Humic acids isolated from seven lignite samples from six European coal basins were characterized using spectral methods and elemental analysis and compared with each other. X-ray photoelectron spectroscopy and fluorescence spectrometry are not commonly used for the investigation of lignite humic acids, although they may provide relevant information. Comparison of the examined lignite humic acids shows that they are very similar to each other in chemical nature regarding the at least degree of aromaticity, molecular weight, and the distribution of functional groups. Fluorophores of lignite humic acids lie within the A region with typical maxima centred in the range 255-265/460-510 nm. EEM spectra have the character of fingerprints for humic acids, and lignites (as the starting material). In this work, the capacity of lignite as a parent source of humic acids for agricultural applications is appreciated mainly on the base of extractability and ash content.