Preparation Of Core-shell Structured Magnetic Adsorbents And Its Application In The Removal Of Heavy Metals From The Wastewater

With the rapid development of industrialization and social economy,heavy metal pollution has become a major environmental threat.Wastewater discharge is one of the main bases of heavy metal pollution in the aquatic system.Adsorption is an effective method to separate heavy metals and other toxic and harmful substances from wastewater.Therefore,obtaining new and efficient adsorption materials has become the research focus of wastewater heavy metal treatment.In this paper,through uniform design and response surface method?RSM?,the preparation conditions of amino functionalized core-shell structure adsorbent and core-shell structure rare earth element doped zirconia were optimized,and the synthesis method of heavy metals copper,lead,zinc and arsenic was developed The main conclusions are as follows:1)The magnetic Fe₃O₄ were synthesized by one-step solvothermal method,then by using anhydrous ethanol as solvent,TMAOH as auxiliary agent,TEOS as silicon source,and APTES for amino functional groups,Fe₃O₄@m Si O₂-NH₂was prepared by sol-gel method.Uniform design U14*?14⁵?and response surface method?RSM?were used to optimize the synthesis ratio.According to the results of TEM,SEM,N₂ adsorption desorption test,VSM and XRD,it was found that the best coating effect was obtained when the relative molar ratio of TMAOH:TEOS:APTES:Fe₃O₄ was 5:4:6:0.45.The results of EDS and elemental analysis confirmed the success of amino group coating,VSM magnetization after surface modification was 32emu/g,BET results show specific surface area is 236m²/g,and the pore volume is 0.126cm³/g.2)The removal of Cu?II?,Pb?II?and Zn?II?by Fe₃O₄@m Si O₂-NH₂ was studied.The optimal initial p H value of the adsorption test system is 6.The isothermal adsorption results show that Langmuir model and Redlich Peterson model are more suitable than Freundlich model to describe the adsorption behavior of heavy metals.Cu²⁺,Zn²⁺and Pb²⁺are mainly single molecular layer chemisorption.When the temperature is 25?,the initial concentration is 5mg/L,the saturated adsorption capacity of Cu²⁺,Zn²⁺and Pb²⁺can reach25.3mg/g,24.2mg/g and 54.6mg/g,respectively.From the fitting curve of the model,the adsorption process is more in line with the quasi second order kinetic model,and the suitable reaction time is 60 minutes.The?G value of heavy metal adsorption is negative,while the?H and?S values are positive,indicating that the adsorption is spontaneous endothermic reaction and presents"entropy driven"effect.The study of adsorption mechanism shows that N atom on amino group is coordinated with metal ion to form stable chelate and realize metal ion removal.3)Fe₃O₄@m Zr O₂?Re=Y/La/Ce?was prepared from zirconium butanol,yttrium nitrate,lanthanum nitrate and cerium nitrate.By using uniform design U14*?14⁵?and response surface analysis,the use amount of Zirconium butanol was determined;by using L9orthogonal design table,the doping ratio of rare earth elements was determined.Based on the results of TEM,SEM,N₂adsorption desorption test,VSM and XRD,the appropriate molar ratio of Fe₃O₄:TMAOH:Zirconium butanol:Y:La:Ce is 1:12:11:0.11:0.02:0.08.The composite materials are mostly spherical particles.The outer layer of zirconium is mainly in the form of amorphous zirconia,which has good magnetic separation performance,specific surface area and pore structure.The magnetic saturation strength is about 10emu/g,specific surface area is 263m²/g,porosity is 0.156cm³/g,and the surface has rich hydroxyl groups.4)The removal of As³⁺and As⁵⁺by Fe₃O₄@m Zr O₂?Re=Y/La/Ce?was studied.The optimal initial p H values of the system were 5(As⁵⁺)and 6(As³⁺).The results of isotherm curves and fitting equation parameters show that Langmuir model and Redlich Peterson model fit well,while Freundlich model has a low fitting degree.The arsenic removal of the material is mainly characterized by single molecular layer adsorption.When the temperature is 25?,the initial concentration is 5mg/L,the saturated adsorption capacity of As³⁺and As⁵⁺can reach 20.3mg/g and 28.9mg/g,respectively.From the fitting curves of the models,the adsorption process is more favors the quasi second order kinetic model.The adsorption of arsenic on materials is mainly spontaneous endothermic reaction.The diffusion in particles,the diffusion in liquid membrane and the adsorption on adsorbent surface will affect the adsorption process,accompanied by the replacement of OH^-on the surface of materials.5)The regeneration methods and efficiency of both materials were studied.For Fe₃O₄@m Si O₂-NH₂,dilute nitric acid and Na HCO₃ were used as regeneration solutions,where material first washed with dilute HNO₃ for 3 hours at room temperature,and then neutralized with Na HCO₃.After seven regeneration cycles,the adsorption efficiency of Fe₃O₄@m Si O₂-NH₂ on Cu²⁺,Pb²⁺and Zn²⁺was 81.21%,81.13%and 80.34%,respectively.For Fe₃O₄@m Zr O₂?Re=Y/La/Ce?,Na OH was used as regeneration solution,when the concentration of Na OH is 0.15mol/l,the adsorption efficiency of adsorbents for As³⁺and As⁵⁺was 75.15%and 77.59%,respectively.The excellent regeneration performance of magnetic core-shell structure adsorbent was demonstrated.This paper has 64 Figures,37 tables,202 references.