Study of water-extractable fractions from South Moravian lignite

Abstract

Lignite can be applied directly in natural form on agricultural fields as a soil conditioner. However, there is little information on leaching of risky compounds by its interaction with water. South Moravian lignite was therefore extracted with water at 25 °C and 2.3 % of water-soluble fractions were obtained from lignite corresponding to 0.3 % of total organic carbon. All ten fractions form aromatic and aliphatic structures with oxygen-containing functional groups such as carboxyl groups, alcohols, ethers, esters, can be characterized as fulvic-like and humic-like substances. According to the XPS spectra, the fractions contain two nitrogen forms, one of which is ascribed to pyrroles and the second is related to protonated amines or quaternary nitrogen. Analysis at molecular level showed that the fractions contain compounds such as benzene carboxylic acids and their derivatives, small aliphatic diacids, fatty acids and polyols. Most of the identified molecules reflect clearly the presence of microbial remains in the lignite structure since microbial activity during coalification is well known. The differences between the individual fractions are negligible, especially after 21 days of extraction. From environmental point of view, it seems that the identified compounds do not represent a toxic risk.