Exploration of the H₂O₂ Oxidation Process and Characteristic Evaluation of Humic Acids from Two Typical Lignites

To study the effect of H₂O₂ on the content and properties of humic acids (HAs) in lignites, the experimental conditions including oxidation time, H₂O₂ concentration, and the solid-liquid ratio were investigated. Under the optimum oxidation conditions, the contents of HAs of YL and HB lignite were 45.4 and 40.9%, respectively. The HAs extracted from oxidized and raw lignites were characterized and compared. The results showed that the HAs extracted from oxidized lignites contain more total acidic groups, carboxyl groups, and aliphatic carbon than that in HAs extracted from raw lignites, and their hydrophilic-hydrophobic index value is higher and thermooxidative stability is better than those in HAs extracted from raw lignites. In addition, the composition of polycyclic aromatic hydrocarbons and fluorophore types in HAs extracted from oxidized lignites are similar to the HAs extracted from raw lignites. The results indicated that the oxidation operation can increase the content of HAs in lignites, and simultaneously increase the content of oxygen-containing functional groups and biological activity of HAs, which provided a reference for the subsequent application of HAs.