长期石油污染土壤中胡敏酸的结构表征:热分析和软X射线近边吸收谱

Structural Characteristics of Humic Acids from Long-term Petroleum Contaminated Soil: DTA, TG and C-1s NEXAFS Spectroscopy

对一口开采约20年的废弃油井,在距离井口0.5、1.5、3.5、5.5和7.5 m处进行采样,采用差热-热重分析(DTA-TGA)和同步辐射软X射线近边吸收谱(C-1s NEXAFS)方法,研究了长期不同程度石油污染土壤中胡敏酸(HA)的结构特征。结果表明:随着与油井口距离的减小,HA的中温和高温放热峰的反应热及热失重增加,高温放热峰/中温放热峰比值增大;软X射线近边吸收谱显示,HA的芳香碳和羧基碳含量增加,脂族碳含量以及脂族碳/芳香碳比值下降。上述结果说明,随石油含量增加,HA的脂族性降低而芳香性增强。C-1s NEXAFS用于HA的结构表征是可行的,能够揭示出不同程度石油污染土壤中HA结构特征的变化规律。

An abandoned petroleum well which had been exploited for about twenty years in Songyuan city of Jilin Province, China, was selected to investigate the structural characteristics of soil humic acid （HA） under different petroleum contamination levels. Surface （0-20 cm） soil samples were collected at 0.5, 1.5, 3.5, 5.5 and 7.5 m depths from well head. HA were extracted with 0.1 mol/L NaOH and 0.1 mol/L Na4P207 and were characterized with differential thermal-therrnogravimetric analysis （DTA-TGA） and synchrotron-based soft X-ray near-edge adsorption （C-ls NEXAFS） spectroscopy. With the decrease in the distance of soil from well head, the reaction heat value and weight loss at both moderate and high temperature exothermic peaks from the DTA-TGA of HA increased, and the heat ratio of the high to moderate temperature exothermic regions increased. The C-ls NEXAFS data suggested that the relative contents of aromatic C and carboxyl C increased, while that of aliphatic C and the ratio of aliphatic C to aromatic C decreased. These results showed that aliphaticity of HA decreased while aromaticity increased with the increase in petroleum content. The results obtained by C-ls NEXAFS spectroscopy were mainly corresponding with those obtained by chemical analysis, thermal analysis, FTIR and ^13C CPMAS NMR spectroscopy, which indicated that C-ls NEXAFS had a potential in characterizing the structural changes of HA in soil with different petroleum contamination levels.