Removal Mechanism Of U(Ⅵ) From Aqueous System By Sulfurized Green Nano-Zero-Valent Iron

Nano-zero-valent iron（nZVI）has been widely used in the remediation of polluted water due to its excellent reduction and adsorption properties.However,there are some defects in the process of preparation and use,such as high energy consumption,secondary pollution,easy agglomeration and deactivation.Green synthesis of nZVI can make up for the shortcomings of high energy consumption and secondary pollution in the process of preparation.Vulcanization modification can effectively overcome the shortcomings of easy agglomeration and deactivation of nZVI in the process of use.In order to repair the polluted water,this experiment selected U（Ⅵ）as the target pollutant to explore whether the sulfurization modification can improve the reaction activity of Green-nano-zero-valent iron（G-nZVI）and U（Ⅵ）.Combined with characterization to analyze the influence of sulfurization modification on G-nZVI activity.To explore the removal mechanism of U（Ⅵ）in aqueous solution by modified G-nZVI.Combined with response surface methodology to optimize the treatment of U（Ⅵ）with sulfide modified green nano-zero-valent iron（S-G-nZVI）in waste water.The optimal reaction conditions and the interaction among the factors were obtained.It provides a theoretical basis for the further development of S-G-nZVI in the remediation of polluted water.The specific conclusions are as follows:（1）Using sunflower extract as the reducing reagent and Na₂S₂O₃ as the vulcanizing reagent,S-G-nZVI with different S/Fe ratios were prepared by a one-step method.The study found that an appropriate S/Fe ratio（0.10）can improve the reaction activity of S-G-nZVI and U（Ⅵ）.The sulfidation modification can increase the pH activity range of the S-G-nZVI.S-G-nZVI（S/Fe=0.10）had a higher removal rate of U（Ⅵ）than G-nZVI in the pH range of 2-8.Increasing the temperature is conducive to the progress of the reaction.Some common anions and cations(HCO₃^-,CO₃^2-,Cu²⁺,Mg²⁺,Ca²⁺,Ba²⁺)in the aqueous solution will inhibit the reaction of S-G-nZVI with U（Ⅵ）.Under the optimal reaction conditions（S/Fe=0.10,pH=4,temperature=40℃,dosage=4 g/L,reaction time=150 min）,the maximum removal rate of U（IV）in aqueous solution by S-G-nZVI was 91.82%.Kinetic and thermodynamic analysis showed that the removal process of U（Ⅵ）by S-G-nZVI is mainly chemical adsorption and monolayer adsorption.（2）According to the results of single factor experiments,the optimal reaction conditions for the removal of U（Ⅵ）from wastewater by S-G-nZVI at room temperature are as follows:S/Fe=0.10,dosage=4g/L,pH=4,reaction time=60 min.Which is basically the same as the reaction conditions of S-G-nZVI for removal of U（Ⅵ）in aqueous solution,Under the optimal reaction conditions,the removal rate of U（Ⅵ）in wastewater by S-G-nZVI can reach 71.20%.According to the results of software fitting,the response surface analysis shows that the influence of various factors on the removal of U（Ⅵ）in simulated wastewater is as follows:reaction time>dosage>s/Fe ratio>pH.Combined with experiments,it is proved that the response surface software fitting model can be used to analyze the treatment of U（Ⅵ）containing wastewater by S-G-nZVI.（3）Scanning electron microscope（SEM）and Specific surface area analysis show that vulcanization modification can inhibit the agglomeration of G-nZVI,increasing the specific surface area of G-nZVI,and improving its removal of U（Ⅵ）.X-ray energy spectrometer（EDS）and Fourier Infrared Spectroscopy（FTIR）analysis show that S-G-nZVI surface contains organic groups（-OH,CH₃-CO-,C=O,C-O）in the plant extract,and these organic groups also participate in the reaction.X-ray electron diffraction（XPS）analysis shows that the removal mechanism of S-G-nZVI on U（Ⅵ）is adsorption and reduction,of which adsorption is the main one.