Preparation Of MIL-101-NH₂@PVDF Composite Membrane Material And Its Adsorption Of Rare Earth Elements In Waste Phosphor

Rare earth elements are widely used in superconductors,aerospace,electronic products,sensors and catalysis due to their unique electronic structure,physical and chemical properties and excellent optical,electrical,magnetic,thermal and other properties.With the development of economy,the demand for rare earth elements has increased dramatically around the world.However,rare earth elements are scarce,unevenly distributed and non-renewable in the world.Therefore,it is of great significance to find an effective method to extract rare earth elements for the development of science and technology in China.Rare earth phosphor powder as an important raw material of electronic light-emitting products,widely used in liquid crystal display,diode and fluorescent lamps,waste contains a large number of rare earth elements in rare earth phosphor cerium(yttrium europium,terbium,etc.),from the waste fluorescent powder recovery of rare earth,rare earth resources in China's sustainable development,energy conservation and environmental protection is of great importance.Metal-organic frameworks(MOFs)are a kind of porous inorganic-organic hybrid crystalline materials,which are self-assembled with carboxylic acid or nitrogen-containing organic ligands by metal ions or metal ion clusters.It has a large specific surface area,uniform and adjustable pore size,good thermal stability,and other characteristics,and has significant advantages in adsorption and separation.The post-modification method can change the pore channel of MOFs and change the properties of the pore,improve the adsorption force with the adsorption object,and achieve efficient separation.Compared with the traditional separation technology,membrane separation technology has the advantages of no phase change,less energy consumption,simple separation process,high separation coefficient,wide application range,can be carried out at room temperature,and can effectively avoid secondary pollution.Based on the excellent selectivity and recognition performance of MOFs for metal ions,this paper proposes the post-modification design and synthesis of MOFs with specific molecular recognition performance for rare earth elements contained in waste phosphors and supports them to form a membrane,to achieve efficient and green extraction and separation of Y and Eu from acid leaching solution of waste phosphors.The main contents of this paper are as follows:1.Firstly,the acid leaching method was used to leach yttrium and europium ions from waste phosphors.The effects of different leaching times,hydrochloric acid concentration,leaching temperature,and solid-liquid ratio on the leaching rate of rare earth element yttrium and europium ions in phosphors were investigated,and the leaching process kinetics was analyzed.The results show that under the optimal conditions of 60 min leaching time,6 mol/L hydrochloric acid concentration,80?leaching temperature,and 10:1 liquid-solid volume ratio,the maximum leaching rates of Y and Eu are 99.31% and 88.5%respectively,and the leaching process is controlled by diffusion.2.MIL-101-NH₂MOFs were synthesized by the solvothermal method.DGA-MIL-101-NH₂ MOFs were prepared by post-modification with diethanol anhydride(DGA).The materials were characterized by FT-IR,XRD,TEM,and TGA.The recognition properties of metal ions were analyzed by fluorescence spectrum.The products were prepared by blending method DGA-MIL-101-NH₂@PVDF Composite membrane,The adsorption properties of Y and Eu in acid leaching solution and simulated solution of waste phosphor were investigated.The results showed that:under the optimal conditions of p H 4,40% DGA-MIL-101-NH₂ loading,2 h adsorption time,14.946 mg/L and 1.008 mg/L Y and Eu initial concentration,the maximum adsorption capacity of Y and Eu reached 991.7 ug/g and 98.76 ug/g respectively.It can be seen from the results of dynamic analysis DGA-MIL-101-NH₂@PVDF The adsorption process of Y and Eu ions on the composite membrane accords with the first-order kinetics.The Langmuir model and Freundlich model were used to fit the adsorption equilibrium data DGA-MIL-101-NH₂@PVDF The results show that the adsorption of yttrium and europium on the composite film conforms to the Freundlich model and belongs to the heterogeneous surface adsorption.The results show that the composite membrane has good reusability.3.PMIDA-MIL-101-NH₂ MOFs were prepared by PMIDA post-modification with MIL-101-NH₂ MOFs as matrix material.The materials were characterized by FT-IR,XRD,TEM,TGA,etc.the recognition properties of metal ions were analyzed by fluorescence spectrum,and the prepared MOFs were prepared by blending method PMIDA-MIL-101-NH₂@PVDF Composite membrane,The results showed that under the optimal conditions of p H 4,30%PMIDA-MIL-101-NH₂ loading,adsorption time of 3 h,initial concentration of Y and Eu ions of 14.946 mg/L and 1.008 mg/L respectively,the maximum adsorption capacity of Y and Eu was 526.6 ug/g and 60 ug/g,respectively.Dynamic analysis shows that PMIDA-MIL-101-NH₂@PVDF The adsorption process of Y and Eu ions on the composite membrane was following the second-order kinetics.The Langmuir model and Freundlich model were further used to fit the adsorption equilibrium data,and it was confirmed that the adsorption of yttrium and europium by PMIDA-MIL-101-NH₂@PVDF composite membrane was in line with the Langmuir adsorption isotherm model,which belongs to chemical adsorption and monolecular layer adsorption.The experiment was repeated for five times.The results showed that the PMIDA-MIL-101-NH₂@PVDF composite membrane had good recycling performance.