Experimental Study On Treatment Of Uranium Containing Wastewater With Nanoscale Zero-Valent Iron/Metal-Organic Framework Composites

In the process of uranium mining,large amounts of radioactive wastewaters containing low concentration uranium are produced,which is dangerous for the health of human and the ecological environment.It is an urgent problem for us to search for an efficient and low consumption treatment method.Adsorption method has become a research hotspot due to its low cost,environment-friendly and high selective removal of uranium.The key of adsorption method is adsorption material.Nanoscale zero-valent iron?nZVI?is an environmental friendly material which exhibits high reduction efficiency and reactivity in reaction with heavy metal pollutants.However,nZVI can be easily aggregated and oxidized when exposed to air.In this experiment,nZVI was synthesized via a liquid phase reduction method,for the loading of nZVI onto a crystalline microporous material Zr-based MOFs,UiO-66 to improve the dispersibility and reaction efficiency of nZVI in aqueous solution and realize the function of adjustable skeletons and functional diversity.Three kinds of materials,nanoscale zero-valent iron,metal-organic framework and nanoscale zero-valent iron/metal-organic framework composite,were compared to study the treatment performance of wastewater containing uranium.The results of nZVI treatment of uranium-containing wastewater showed that the maximum removal rate of U?VI?was 80.36%at a temperature of 303 K,pH of 6,a dosage of 0.2 g�L^-1 of nZVI,reaction time of 120 min and an initial U?VI?concentration of 10 mg�L^-1.FTIR and XRD characterization results indicate the successful preparation of nZVI.The pseudo-second order kinetic equation and Freundlich adsorption isothermal model can fit the adsorption process well.FTIR and XRD characterization results indicate the successful preparation of Zr-based metal-organic frameworks UiO-66 by a solvothermal method.The experimental results of UiO-66 adsorption U?VI?showed that the maximum removal rate of U?VI?was 88.18%at a temperature of 303 K,pH of 7,a dosage of 0.15 g�L^-1 of UiO-66,reaction time of 60 min and an initial U?VI?concentration of 10 mg�L^-1.pH is an important factor affecting the adsorption of U?VI?by UiO-66.The pseudo-second order kinetic equation and Langmuir adsorption isothermal model can fit the adsorption process well.nZVI/UiO-66 was synthesized by a co-precipitation method.The maximum removal rate of U?VI?was 96.36%at a temperature of 303 K,pH of 6,a dosage of 15 mg of nZVI/UiO-66,reaction time of 120 min and an initial U?VI?concentration of 10 mg�L^-1.The results of BET show that the specific surface area decreases after composite.The adsorption process of U?VI?by nZVI/UiO-66 is a spontaneous endothermic process.The pseudo-second order kinetic equation?R²=1.000?and Freundlich adsorption isothermal model?R²=0.979⁰.984?can fit the adsorption process well.The maximum adsorption capacity fitted by Langmuir was380.228 mg�g^-1.The mechanism was mainly related to adsorption of U?VI?from UiO-66 and reduction of U?VI?by nZVI.The Zr-O bonds were shown to play a vital role in the uranium removal.The results of adsorption and desorption experiment showed that 0.1M Na₂CO₃ was the best desorption solution for nZVI/UiO-66.The uptake rate could be maintained at around80%after 5 cycles of use,which indicates that nZVI/UiO-66 is expected to be a potential functional material for the treatment of low concentration uranium wastewater.