Study On Nanoscale Zero-valent Iron Loated In Pottery Granules For Heavy Metals Removal

The development of industrial society has aggravated the problem of environmental pollution,in which the pollution of heavy metal ions is a kind of common environmental problems which are harmful to human health.Ceramics and nano zero-valent iron?NZVI?are commonly used in two types of heavy metal polltiontion.Ceramic has a good compatibility with the environment,which alse has large surface area and strong adsorption.The advantages of nano zero-valent iron?NZVI?in the removal of heavy metals are high reactivity and effectiveness.A new kind of porous ceramic loaded NZVI particles was prepared by Technology Company of micro ceramic heavy metals filter.However,it was not clear what the kinetic.thermodynamic models and the related mechanism of heavy metals?such as,As???and Cr????removal by the filter materials were.Therefore,in this paper,a study of the NZVI coated porous ceramic particles?collectively referred to as:the iron coated ceramic particles?was carried out to investigate the microstructure,chemical composition and surface properties.Moreover,factors affecting the adsorption of As???and Cr???,and the kinetics,thermodynamics of Cr???were studied furthermore.The above results revealed the possible mechanisms of the separation processes of As???and Cr???by the materials.?1?In this study,the three samples?ceramic particles.the iron coated ceramic particles?the iron coated ceramic particles after adsorption of As????were taken as the research object.Scanning electron microscopy?SEM?and transmission electron microscopy?TEM?were employed to study the surface morphology,particles size distribution.X-ray energy dispersive spectroscopy?EDS?was employed to characterize element respectively.Surface area analyzer was employed to measure the specific surface area,the volume and size of pore.Raman and Fourier transform infrared?FTIR?spectroscopic were carried out to study the group composition.X-ray diffraction?XRD?and X-ray photoelectron spectroscopy?XPS?were employed to study the variation of the valence state and crystal structure.The above experimental results showed the main components of the three samples were ?-Al₂O₃,and the NZVI were successfully loaded on the surface of ceramic particles in a form of"core-shell" structure.Morever,the surface of NZVI was converted into various forms of iron oxides?FexOy?;As???was successfully adsorbed on the surface of iron loaded ceramic particles;the three kinds of ceramic particles had micro scale and nano scale pores which was less than 60 nm;it was good for removal of arsenic that the iron coated ceramic particles had a larger specific area and pore volume,which was 130.8 m2/g ? 0.407 cm3/g respectively;The intermediates which was produced in the process of Fe⁰ converted into Fe_xO_y made As???oxidized to As???;then there had been complexation between As???? As???and the Fe-O and Fe-OH groups,which generated Fe?H₂AsO₃?₂ and FeAsO₄ precipitates to be removed.?2?The results of adsorption experiments on Cr???by the iron loaded ceramic particles showed the following points.When the pH of solution was blew 7,the Cr???was mainly in the form of HCrO₄^- in the solution,and the adsorption capacity of Cr???on the iron loaded ceramic particles decreased gradually with the increase of pH.The adsorption capacity of Cr???increased with the increase of initial concentration.In the initial stage of reaction,the removal rate of Cr???increased with the increase of initial concentration,while it would declined,when the removal rate of growth beyond the critical value.With the increase of the adsorption time,the removal rate of Cr???would go through a phase of rapid first and then slowly,and finally stop which indicated the adsorption reaction is in equilibrium.The kinetic date for Cr???removal could be well described by pseudo-second order rate model.Moreover,The adsorption procedure included fluid film diffusion and intraparticle diffusion,where the particle diffusion played a decisive role.The adsorption isotherm of Cr???fit Langmuir model well,which indicated the adsorption process might be chemisorptions.Thermodynamic investigations showed the following facts:?the adsorption of Cr???on the iron coated ceramic particles was spontaneous and endothermic;?it confirmed the adsorption belonged to chemisorptions again.?3?The two samples?the iron coated ceramic particles?the iron coated ceramic particles after adsorption of Cr????were taken as a research object.The results showed the following points.The main components of the two samples were ?-Al₂O₃ and Fe₂O₃.The Cr???of the solution was adsorbed on the surface of the iron loaded ceramic particles.The two samples had micro scale and nano scale pores.Morever,the average pore size of the iron loaded ceramic particles was reduced from 12.3 nm to 11.7 nm after adsorption of Cr???.The specific surface area?the pore volume of the iron loaded ceramic particles which adsorbed Cr???were reduced.The possible reasons made the specific surface area decreased from 137.8 m2/g to 130.1 m2/g and the pore volume decreased from 0.434 cm3/g to 0.400 cm3/g were the ferrite reacted with Cr???to form a ferrochromium hydrate,clogging part of the pores.During the adsorption of Cr???by the iron loaded ceramic,part of Cr???were reduced to Cr???by Fe⁰ and Fe²⁺,and then the Cr?OH?₃ precipitate were removed.And most of Cr???would complexed with Fe-OH at the same time,resulting in Cr_xFe_y?OH?_z being removed.This paper revealed the mechanism of adsorption of heavy metal ions by the NZVI coated porous ceramic particles,building the corresponding adsorption kinetics,thermodynamic model and material characterization method.It was a great significance to further optimize the material characteristics of the ceramic particles.