Improving extraction yield of humic substances from lignite with anthraquinone in alkaline solution

Based on the characteristics of the lignite sample, effects of assistant anthraquinone (AQ) on extraction yield of humic substances (HS) and the action mechanisms of AQ in alkaline condition were studied by Fouvier transform infrared (FT-IR) spectroscopy. The results indicate that assistant AQ can not only increase the extraction yield of HS but also reduce the alkali dosage (NaOH) as well as the extraction temperature and extraction time. Under the optimal conditions of alkali dosage of 9%, AQ dosage of 0.75%, extraction temperature of 80 °C, extraction time of 30 min, stirring speed of 600 r/min and solid-to-liquid ratio of 1:3, the extraction yield of HS reaches 80.08%, which is increased by more than 20% compared with the conventional extraction. FT-IR spectra show that AQ is able to prevent dissolved HS from being destroyed into undissolved substance by alkali and HS obtained in the presence of AQ possesses more groups of -COOR and -COOH than that obtained without AQ.