Abstract:In order to explore the effect of heating on content and structure of humic acid in soil, three soil samples were heated at 200, 250, 300 ℃ for 2, 4, 6 h, respectively. UV-VIS spectra, 3D fluorescence and infrared spectroscopy were used to demonstrate the changes of humic acid (HA) in soil before and after heating. The results show that the content of humic acid drops and ratio of HA to fulvic acid (FA) in soil after heating increases while the heating temperature and time increase. It indicates that heating can increase the proportion of aromatic parts, the degree of humification and the average molecular weight of humic acid, which makes humic acid more stable. For 3D fluorescence spectra, the fluorescence peak intensity of HA rises with the increase of heating temperature, which indicating that the aromatic substances in HA increase. The number of functional groups of HA is changed after heating. HA possesses more aliphatic components when the soil samples are heated on 200 ℃ or 250 ℃ for less than 6 h, but the aliphatic components decreases while the aromatic components increase when the soil samples are heated at 300 ℃. What''s more, after heating at 250 ℃ for 6 h and 300 ℃, carbohydrates or polysaccharides are decomposed in large quantities. Therefore, in terms of never damaging the soil''s own fertility and self-purification capacity, the heating time of 200 ℃ or 250 ℃ for no more than 6 h may be the most suitable heating intensity for thermal remediation of soil.