| Currently faced with different levels of soil heavy metal pollution in our country,the type of metal arsenic pollution situation is relatively serious,high degree of soil pollution in some areas,food and drinking water arsenic events arising from the growing.With the development of society,nano-scale materials have been widely applied to the environment of heavy metal repair,in which As Pollution control has achieved better results in the management of environmental,.due to the large specific surface area,small particle size and high reactivity physical and chemical properties of nano-zero-valent iron(NZVI).In this study,Chitosan was used to prepare chitosan-based nanosized zero-valent iron(C-NZVI)by the modification of zero-valent nano fibers.Firstly,kinetics,isothermal adsorption experiments and competition experiments were conducted to investigate the effect of the adsorption of As(?)in solution system.Secondly,the dissolution characteristics of As contaminated soil and in-situ adsorption of As in soil solution by C-NZVI on-line system were explored under long-term flooding conditions.On the basis of this,under the flooding condition,the dissolution characteristics of As in the soil were regularly drained and the effluent As was adsorbed and filtered by Fe-based adsorbent to be purified.Then,it was extracted by C-NZVI on-column system Pore water As,enhanced flooding with clear flooding----Drainage--Repair technology of activated As in soil by the combined technology of column system.The main conclusions are as follows:(1)The adsorption of As(?)by C-NZVI accords with the quasi-first order kinetics and the Langmuir adsorption isotherm model.When the initial concentration of As(?)is 250 mg/L,As(?)removal rate can reach 95%;Langmuir model fitting maximum adsorption value of 145.1 mg/g.(2)C-NZVI can remove 99%of the initial concentration of 5 mg/L As(?)when the concentration of competitive K2HPO4,H3BO3,Na2SiO3 and CH3COOH is 0.05-0.5 mmol/L.(3)The removal rate of solution As in the C-NZVI column system was as high as 61.2%,while C-NZVI remaining in the solution system only decreased 27.2%of As.(4)Long-term flooding and turning the soil can effectively speed up the dissociation of As in soil,with the highest dissolution rate of As being as high as 18.9 mg/kg and As(?);The adsorption capacity of C-NZVI column system in the later stage is obvious.After flooding,the content of solid As in the treatment was reduced by 31.8%compared with the original soil.(5)Fe in C-NZVI system does not dissolve in a large amount during the flooding process,reducing the secondary pollution.At the same time,the extraction technology can selectively adjust the application density of the extraction column and the reaction extraction time.(6)The addition of fortifier can effectively promote the reduction and dissolution of As in the soil.The removal rate of As(341?g/L)from the effluent As(34?g/L)is higher than that of other three kinds of adsorbents under the same application ratio.With different concentrations of C-NZVI after the enhanced efflux As removal,the removal efficiency is above 74%,while C-NZVI at the same time overlying water P,Si efficient removal.(7)As compared with the original soil,soil As content in the treatment of mixing and mixing+strengthening agent significantly decreased by 23.4%and 26.7%under the combination of flooding and enhanced dissolution-drainage technology;and the C-NZVI column The system can effectively remove soil liquid phase As.The above experimental results show that the high efficiency of Flooding Enhanced Dissolution-Drainage-Column Load System combined technology was an important way to repair arsenic contamination in paddy fields. |
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