Coal is oxidized by artificial oxidation (such as air, ozone or nitric acid) to form a regenerated humic acid, for example, the product of mild oxidation of nitric acid in coal is called nitro.
The method of extraction is to treat with acid first, remove some minerals, and then extract with dilute alkali solution, and then add acid acidification, and the humic acid precipitation can be obtained. According to the solubility of humic acid in solvents, it can be divided into three components: the part that is soluble in acetone or ethanol is called the brown rot acid; The insoluble in acetone is called black rot; The part that is soluble in water or dilute acid is called fulvic acid. The basic structure of humic acid macromolecules is aromatic ring and fat ring, which is composed of carboxyl, hydroxyl, carbonyl, quinone, methoxyl, etc. It has the function of exchange, adsorption, complexation and chelation with metal ions; As a polyelectrolyte in dispersive system, it has the function of coagulation, glue solution and dispersion. Humic acid molecules have a certain number of free radicals, which have physiological activities.