Study On The Adsorption Behavior And Mechanism Of U(Ⅵ) By Amino And Phosphate Modified Materials

The development of nuclear power has promoted utilization of uranium resources to a new stage.However,it is inevitable to result in environmental pollution problems during the process of the uranium mining and utilization.Because uranium-containing wastewater is highly toxic,it will cause damage to the kidneys,respiratory system,bones and etc.And the decay of uranium causes radiation effects,especially internal radiation effects can lead to cancer.Developing radionuclide wastewater treatment method is one of the most important research topics in the world.Compared with other removal methods,the adsorption is low cost,high efficiency,and simple operation.It is suitable to remove U(Ⅵ)in aqueous solutions.Therefore,in this paper,based on cheap substrate materials,we purposefully designed two strategies of modification to enhance the adsorption ability and selectivity of the adsorbents for U(Ⅵ),and discussed the adsorption mechanism.The main research contents are as follows:(1)In this work,moso bamboo was pyrolyzed to produce biochar,and polyethyleneimine(PEI)modified alkali/acid treated biochars(PEI-alkali/acid-biochar)were used to remove U(Ⅵ)in aqueous solution.The objective of the current study was to study the adsorption performance and mechanism of PEI-alkali/acid-biochar for U(Ⅵ)at different environmental conditions(temperature,pH,ionic strength,etc.).PEI was successfully attached on the alkali/acid-biochar surface according to the characterization analysis.PEI provided amounts of amino groups for U(Ⅵ)adsorption,which conferred high adsorption capacity.The U(Ⅵ)adsorption was obviously influenced by pH at pH<6.0.The U(Ⅵ)adsorption on PEI-alkali/acid-biochar was mainly controlled by the complexation between U(Ⅵ)and amino groups,which was verified by FTIR and XPS analyses.The adsorption kinetic of PEI-alkali/acid-biochar indicated 8 h is enough to achieve equilibrium and their maximum adsorption capacity calculated by the Langmuir model were 212.7 mg/g for PEI-alkali-biochar and 185.6 mg/g for PEI-acid-biochar.The U(Ⅵ)adsorption processes on PEI-alkali-biochar and PEI-acid-biochar were both exothermic and spontaneous.The PEI-alkali/acid-biochar adsorbed could be regenerated by acid elution,which kept its high adsorption capacity after five adsorption-desorption cycles.In comparison to acid treatment,the alkali treatment was less corrosive and more economic.Alkali treatment may be the optimal route for the modification of PEI treated biochar,and PEI-alkali-biochar show higher U(Ⅵ)adsorption capacity than PEI-acid-biochar.Therefore,The PEI-alkali-biochar can be regarded as a promising material for U(Ⅵ)removal in practical application.(2)In this study,3D flower-like phosphate functional layered double hydroxide(phos-LDH)was fabricated by a one-pot hydrothermal technique.The adsorption performance and selectivity of this adsorbent for U(Ⅵ)were minutely studied under different environmental factors(temperature,pH,ionic strength,contact time and so on).Characterization technologies,including SEM,TEM,XRD,FTIR,XPS,BET and zeta potential,were performed to understand the adsorption mechanism of U(Ⅵ)by phos-LDH.The purpose of this work was to seek a powerful and high selective nano-adsorbent for remediation of U(Ⅵ)-containing wastewater.The intercalation of hexametaphosphate can decrease the surface potential and introduce phosphate groups,leading to the outstanding adsorption capability and ultrafast adsorption equilibrium of phos-LDH for U(Ⅵ).The kinetic adsorption process obeyed the general order model.The adsorption isotherms can be better fitted by Langmuir model and the maximum adsorption capability was calculated to be 923.1 mg/g at 298 K,which was superior to previous reported adsorbents.The thermodynamic parameters illustrated the U(Ⅵ)adsorption on phos-LDH was spontaneous and endothermal.The adsorption mechanism was ascribed to the electrostatic attraction as well as the inner-sphere complexation between functional groups(hydroxyl and phosphate groups)and U(Ⅵ).The phos-LDH can be simply synthesized by a one-pot hydrothermal technique and significantly decrease its cost.In conclusion,this work reported an efficient and low-cost adsorbent that could be used in U(Ⅵ)adsorption from real radioactive wastewater.