Preparation Of Magnetic Nano–Sized Illite–Smectite Clay For Adsorption Of Heavy Metallic Ions In Aqueous Solution

Wastes（i.e.,water,gas and residue）discharged from industrial production contain heavy metallic ions.The toxic pollution of heavy metals is one of the most urgent environmental problems.If heavy metallic ions are ingested by human or accumulated in the human body,they will cause multiple organ failure,cardiovascular disease or nervous system damage.The exsiting methods of removing heavy metallic ions in aqueous solution are chemical precipitation,electrochemitry,physical adsorption,ion exchange,etc..Physical adsorption is one of the effective methods to remove heavy metallic ions in aqueous solution due to its advantages like high efficiency and easy operation.Clay mineral that is a silicate mineral with large specific surface area and intense ion exchange ability can be used as an adsorption material for removal of heavy metallic ions in aqueous solution.However,it is difficult to separate the clay mineral from solution after the adsorption of heavy metallic ions due to the small particle size of clay mineral material,thus resulting in the restriction of the reuse and recycling.Recent work has dealt with the preparation of magnetic clay,which can be separated in external magnetic field.It is reported that illite/smectite clay as a clay mineral between illite and montmorillonite can be used to adsorb heavy metallic ions effectively.The purpose of this desertation was to prepare a magnetic nano-sized illite/smectite clay for the adsorption of heavy metallic ions in aqueous solution.In the first chapter,sources,hazards and treatment methods of heavy metal pollution in aqueous solution were represented.Recent work on the adsorption of heavy metallic ions with clay minerals and magnetic clay minerals,the existing preparation methods of magnetic clay minerals as well as the structure and physicochemical properties of illite-smectite clay were described.In addition,the research purposes and contents of the desertation were also given.In the second chapter,raw materials,reagents,experimental equipment and instruments used（i.e.,X-ray sedimentation particle size analysis,X-ray diffraction（XRD）,scanning electron microscopy（SEM）,vibrating sample magnetometry（VSM））were presented.The principles of experimental equipment and instruments and the corresponding test conditions were introduced.In the third chapter,a magnetic nano-sized illite/smectite clay was prepared by a chemical coprecipitation method.The effects of pH value,n(Fe³⁺)/n(Fe²⁺),reaction temperature,stirring speed and addition amount of nano-sized illite/smectite clay on the specific saturation magnetization and adsorption performance of Cd²⁺,Pb²⁺ were investigated.According to the experimental results obtained at each parameter test above,an orthogonal test L₉（3⁴）was designed to investigate the specific saturation magnetization and adsorption performance of Cd²⁺,Pb²⁺ of magnetic nano-sized illite/smectite clay with respect to the effects of n(Fe³⁺)/n(Fe²⁺),reaction temperature,addition amount of nano-sized illite/smectite clay at p H value of 10 and stirring speed of 400 rpm.The greater specific saturation magnetization and removal rate of Cd²⁺ and Pb²⁺ were obtained under the optimal parameters(i.e.,n(Fe³⁺):(Fe²⁺)of 6:3,reaction temperature of 60 ℃,and m（I/S）:m（Fe₃O₄）of 1:1).The magnetic nano-sized illite/smectite clay was characterized by XRD,SEM,VSM and Fourier transform infrared spectroscopy（FTIR）,respectively.The results show that the Fe₃O₄ nanoparticles can be effectively loaded on the surface of the nano-sized illite/smectite clay via chemical coprecipitation,the specific saturation magnetization of magnetic nano-sized illite/smectite clay is 26.77 emu/g and the composite products can be separated from aqueous solution in external magnetic field.In addition,the magnetic nano-sized illite/smectite clay was also prepared by a mechanochemical method,nano-sized illite/smectite clay and Fe₃O₄ particles were ground mechanically in a high-energy density stirred beads mill.The effect of milling time on the particle size,specific surface area and specific saturation magnetization of composite products was studied.The composite products were characterized by XRD,SEM,VSM,and specific surface area analysis,respectively.The results show that Fe₃O₄ particles are effectively attached on the surface of nano-sized illite/smectite clay under the action of intense mechanical force.According to the results by XRD,the diffraction peaks of nano-sized illite/smectite clay and Fe₃O₄ coexist in the composite products,and there are no other phases.The particle size and specific saturation magnetization of composite product decrease,but the specific surface area increases with the increase of milling time.In the fourth chapter,magnetic nano-sized illite/smectite clay composite materials prepared by chemical coprecipitation and mechanochemical methods were used to adsorb Pb²⁺,Cd²⁺ in aqueous solution.The effects of slurry pH value and addition amount of magnetic composite material on the adsorption performance were investigated.The adsorption isothermal was simulated by the Langmuir and the Freundlich models,respectively.The adsorption dynamic behavior was also simulated by the pseudo-first-order kinetic and pseudo-second-order kinetic equations.The magnetic nano-sized illite/smectite clay prepared can effectively remove Pb²⁺ and Cd²⁺ in aqueous solution.In addition,the specific saturation magnetization of the magnetic nano-sized illite/smectite clay prepared by chemical coprecipitation and mechanochemical methods is 26.77 emu/g and 17.74 emu/g,respectively.The experimental results by magnetic separation show that magnetic nano-sized illite/smectite clay after adsorption of heavy metallic ions can be effectively separated from aqueous solution in external magnetic field.Finally,the major conclusions,shortcomings and future research aspects are given based on the experimental results obtained.