| With the rapid development of economy and the depletion of fossil energy,nuclear energy is favored for the characteristics of clean and efficient.The rapid development and exploitation of nuclear energy will inevitably produce a series of low concentration radioactive uranium-containing wastewater,resulting in environmental pollution.In the study of uranium removal and immobilization,the application of zero-valent iron has attracted wide attention of researchers all over the world.However,the characteristics of surface oxidation and agglomeration limited the effective removal of uranium by nano zero-valent ironIn this work,ferric nitrate and ferric chloride were used as iron source,and soluble starch was used as carbon source.By adjusting the mass ratio of iron soluble starch and carbonization temperature,biochar supported nano-zero-valent iron composites(Fe/Cs)were prepared by carbothermal reduction method under N2 atmosphere.XRD,SEM,BET,FT-IR and XPS were used to analyze the phase transformation and properties of zero-valent iron.The effects of different factors on the treatment of uranium-containing wastewater by Fe/Cs were carried out by batch adsorption experiments.Based on the properties,morphology,and uranium valence changes of the adsorbent material before and after the reaction,the mechanism of zero-valent iron on uranium was analyzed.The influence of different factors on the removal of uranium by Fe/Cs and the mechanism analysis in the presence of phosphate were also investigated.The research contents are as follows(1)With a mass ratio of iron-soluble starch at 1:4 and a carbonization temperature at 900 ℃,nanosheets FeCl/C(1:4-900)and nanoparticle FeN/C(1:4-900)with abundant oxygen-containing functional groups were successfully prepared.The specific surface areas are 782.05 m2/g and 204.85 m2/g,respectively,which show mesoporous structures(2)FeCl/C(1:4-900)and FeN/C(1:4-900)were selected as the target adsorbents The optimal pH walues for removing U(VI)were 7 and 6,respectively.In the kinetic adsorption experiment,FeCl/C(1:4-900)and FeN/C(1:4-900)showed excellent adsorption performance for uranium solutions with an initial concentration of 20 mg/L,and the maximum removal efficiency was 96.6%and 96.4%,respectively.The results of the isotherm adsorption experiment datas were fitted to indicate that the adsorption behavior of FeCl/C(1:4-900)and FeN/C(1:4-900)to uranium were conformed to the Langmuir isotherm adsorption model.The maximum adsorption capacities are 34.82 and 55.14 mg/g,respectively.The adsorption.After adsorption of U(Ⅵ),the micro-morphology of FeCl/C(1:4-900)and FeN/C(1:4-900)changed significantly.SEM-mapping confirmed that the fixed element U and Fe were attached to FeCl/C(1:4-900)and FeN/C(1:4-900).XPS showed that 78.1%U(Ⅳ)and 21.9%U(Ⅵ)exist on FeCl/C(1:4-900),82.65%U(Ⅳ)and 17.35%U(Ⅵ)was observed on FeN/C(1:4-900).The removal mechanism of U(Ⅵ)by FeCl/C(1:4-900)and FeN/C(1:4-900)is due to the reduction-adsorption of zero-valent iron(3)In(U-P)+Fe system,when the molar ratio of U(Ⅵ)to phosphate is 1:2(U/P 1:2),U(Ⅵ)could be efficiently removed in the pH range 2-9,and the highest removal efficiency can reach 99%.The reaction process is less affected by temperature,and it fitted well to pseudo-second-order model.Compared with the system without phosphate,the addition of phosphate strengthened the immobilization performance of FeN/C(1:4-900)on uranium,which showed wide applicability of pH The surface morphology of the reaction product in(U-P)+Fe system changed significantly.The SEM images showed that nanosheet structures appeared on the surface of zero-valent iron particles.SEM-mapping clearly showed related elements P and U.Considering the value of U/P consumed,it confirmed that the addition of phosphate promoted the immobilization of U(Ⅵ)by zero-valent iron,generating new complexed products. |
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