“…The humic substances in lignites are traditionally classified into three categories according to their alkaline and acid solubility, including alkali-insoluble, alkali-soluble, and acid-insoluble, and alkali- and acid-soluble components, corresponding to humin, humic acids, and fulvic acids, respectively. , HAs are rich in a variety of oxygen-containing functional groups such as carboxyl, hydroxyl, phenolic hydroxyl, carbonyl, methoxy, and so on . The chemical and physiological activities of HAs are directly related to their molecular weight, structural characteristics, and the type and number of oxygen-containing functional groups . HAs have many properties, such as exchange, adsorption, complexation, and chelation with metal ions, , and are widely used in the agriculture, − industry, environmental management, − medicine, , and other fields. , Therefore, research on HAs is of great significance.…”