| Mercury is one of the global pollutants with persistence, bioaccumulation and toxicity in environment. Mercury can undergo long distance transportation in the atmosphere, even countries with less mercury emissions, as well as low-intensive areas of human activity, may also be subjected to the hazards of mercury pollution. The inorganic mercury can be converted to organic form which may be the most toxic compounds and may endanger human health and safety through the food chain, so an increasing attention was played to the increasing background concentration of mercury. In the past several decades, Asia, especially China, has experienced a rapid economic and industrial development and become the largest atmospheric mercury emission source. Gaseous element mercury can be oxidized to reactive mercury (Hg(Ⅱ)) in the atmosphere and be rapidly deposited and discharged to aqueous and terrestrial systems. Forest ecosystem is an important part of terrestrial system. A large percentage of atmospherically deposited mercury is sequestered by forest surface soil and the forest surface soil may be the most important source of mercury to surface water. Shandong province, China is one of the old industrial provinces with the largest chlor-alkali production capacity and gold mining. Chlor-alkali plants and mining activities are two important source of mercury emissions to the atmosphere and related contamination of soils in their vicinity. Mount Tai, Laoshan Mountain and Fanggan village are the most important forest areas which are around drinking water sources. Therefore, the adsorption/desorption processes in soil for Hg will contribute to know the fate and the behavior of mercury in soil.Warm temperate zone is one of the cradles of our civilization which is rich in biological resources. With the intensification of environmental issues in the modern times, the natural vegetation of the mountains of the region had been destroyed which led to reduction in biodiversity in the region, and biological resources were scarce. Fagaceae Quercus occupies a very important role in the warm temperate forest resources and is the key forest dominant species and constructive species of these regions. Humification processes plays an important role in the process of forest vegetation recovery:humic acid helps to maintain soil nutrients and form soil structure; fulvic acid plays an important role in the promotion of mineral decomposition and nutrient release. Therefore, the research of humification processes has important theoretical significance for the reconstruction of forest vegetation communities.This study investigated the adsorption/desorption characteristics and mechanism of Hg(Ⅱ) on three typical brown soil in the Shandong region and the humification process under Quercus forest of Laoshan region. Results are as follows:(1) Hg(Ⅱ) adsorption isotherms on three soils could be well fitted with both Langmuir and Freundlich equations. The Mount Tai soil had the largest potential adsorption capacity, though with less adsorptive intensity. The desorbed percentages of all soil samples were less than0.6%, which suggested that all soil samples had high binding strength for Hg(Ⅱ). The Mount Tai soil had a higher desorption ratio than the other soils, which indicated that the Hg(Ⅱ) deposited on the Mount Tai soil from atmosphere might easily discharge to surface water through runoff. The Fourier transform infrared (FTIR) spectroscopy was adopted to characterize the soil samples and soil-Hg complexes. The result showed that three soils contained the same function groups. The relative absorbances (rA) of soils-Hg complex changed significantly compared to that of the soil sample, the adsorption of Hg(Ⅱ) on soils mainly acted on the O-H, C-O and C=O groups of soil.(2) Hg(Ⅱ) adsorption isotherms on six HSs could be well fitted with both Langmuir and Freundlich equations. Three humic acids (HAs) had larger adsorption intensity and adsorptive capacity than three fulivc acids (FAs). The desorbed percentages of three HAs were less than2.6%, which suggested that HAs had high binding strength for Hg(Ⅱ). As the HAs shows stronger adsorptive intensity and lower desorption ratio for Hg(Ⅱ), the HAs might play an important role in the adsorption/desorption processes in soil for Hg(Ⅱ). The Fourier transform infrared (FTIR) spectroscopy showed that six HSs contained the same function groups, and the adsorption of Hg(Ⅱ) on HSs mainly resulted from the iron exchange and the formation of hydrogen bonds, and might also take place on the C=O, COO-, O-H and C-O of the HSs. (3) With the process of humification, carboxymethyl hydroxy or alcoholic hydroxyl had experienced a re-generated after a first decomposition process, while an upward trend in the relative content of soil carboxyl compounds, with the increase in soil depth. The relative content of aromatic groups and nitrogen groups remained relatively stable in the process of humification and C-O groups is relatively decreased. Humification process of the humus layer was stabilized; the formation of humic acid had been more mature. The forming process of fulvic acids might accompany a synthesis process, which the carboxyl compounds were first consumed and then synthesized and the polymers with C-O structure were first synthesized and then consumed. |
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