| Groundwater is an important part of geo-environment and major source of drinking water in north China. With the rapid urbanization and industrialization in China, the environmental quality of groundwater is exacerbated, and environmental pollution has become an increasingly striking issue. Therefore, treatment of nitrate pollution to groundwater has become extremely imminent. Currently in China, The major remediation methods of groundwater pollution, especially nitrate pollution include Permeable Reactive Barriers, Extraction and Processing method, etc. These methods can relieve the nitrate pollution to some extent, and has been applied effectively in some certain areas. However, as the pollution of groundwater aggravates, these above-mentioned methods turn out to be not enough capable and economic. Clays minerals widely exist in geo-environment, and almost all clay minerals contain structural iron, which can be reduced to ferrous iron by microorganism and chemical methods. During the iron reduction, the structure of clay minerals stays unchanged, so does the spatial position of the structural iron in clay minerals. The structural iron can thus be utilized as a renewable resource. In this paper this potential renewable resource was treated properbly. its potential ability to remediate groundwater nitrate pollution was investigated.Soil mineralized nitrogen could get into the groundwater through leaching, causing groundwater nitrate pollution. This paper used accelerated diffusion methods to determine soil mineralized nitrogen, and compared the efficiency of KC1extraction method and CaCl2leaching method. Results showed that KC1extraction method has a better efficiency than CaCl2leaching method in leach soil mineralized nitrogen This result provides a basis to measure the soil mineralized nitrogen accurately, and also provides a foundation for the follow-up studies.In this paper, the method for reduction of the structural iron in clay minerals was fully introduced. The structural Fe(Ⅱ) can re-oxidize easily, how to prevent this re-oxidization and keep the content of the structural Fe(Ⅱ) came to be difficult. This paper used Controlled Atmosphere Liquid Exchange (CALE) system to wash the reduced clay minerals under anoxic environment. During the washing process, no structural Fe(II) was re-oxidized. A glove box, used for long-term storage of reduced clay minerals, was also discussed in this paper. These results provided a unified starting condition for clay minerals study, and offered a foundation for long-term studies. Oxidized and reduced natural clay minerals showed no reaction toward nitrate in water. The Coulomb repulsion between negative charged natural clay minerals and negative charged nitrate ion is an immense obstacle to the nitrate reduction. This research aimed at using polymer cations to intercalate into the interlayer of clay minerals and exchange with cations, so that the polymer-modified clay minerals can overcome the Coulomb repulsion, act strong adsorption to nitrate and degrade nitrate to other less hazardous nitrate group products, N2as an example. The polymer-modified clay minerals may inspire a new research trend in the field of groundwater pollution treatment, especially nitrate pollution treatment. The fact that microorganisms can reduce structural iron in clay minerals are ubiquitous in nature was also discussed. This paper also discussed the mechanism of microbial reduction of structural iron, and summarized the reaction conditions, which make it clear that this microbial reduced clay minerals reduce nitrate in nature can be occurred. At last, some important conclusions were summarized, and also give out fews outlooks about research direction and key points for the future studies. |
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