Study On Nanoscale Zero-Valent Iron Coated In Foam Ceramic For Pb(Ⅱ) Removal From Water

The rapid rate of industrialization as well as urbanization have resulted in many chemicals over manufacturing,which are from natural and anthropogenic sources,drain into the water body and the environment.Some of those chemicals,such as heavy metal,have immense adverse effects on humans and animals.It is universally known that lead（Pb）is a kind of heavy metal with severe toxicity.Pb（II）is not only carcinogenic and toxic to living beings,but also high concentration of Pb（II）is likely to reduce the productivity of farmland as well as increase the risks of spontaneous abortion and natality as well.Therefore,Pb（II）leakage in the water environment has arouse attention of people from all walks of life.Recently,nanoscale zero-valent iron（NZVI）has been widely used as an environmental restoration material on account of its large specific surface area and strong reduction reaction ability.However,NZVI nanoparticles is susceptible to magnetic forces,van der Waals type interactions for aggregating into large chain particles and the oxide layer will be formed on the surface of the particles,which result in poor reactivity and low removal efficiency.Thus,the purpose of this study is to find a restoration technology that stabilizes NZVI particles and improves the reactivity,namely the stabilized NZVI of environmental restoration technology.In order to further explore the applicability of this technology,NZVI particles-supported foamed ceramics（NZVI/FC）,as the research object,was taken in this study.（1）Foamed ceramics（FC）,As a carrier,were used to prepare the supported nanoscale zero-valent iron（NZVI/FC）composite material by liquid phase reduction method and hydrothermal method.FC has so many physical properties such as high compressive strength,high porosity,and large channels.And then,the characteristics and stability of FC,NZVI/FC and NZVI/FC after the adsorption of Pb（II）were analyzed via Scanning electron microscopy（SEM）,X-ray energy dispersive spectrometer（EDS）,X-ray diffractometer（XRD）,Fourier infrared spectroscopy（FTIR）,and X-ray photoelectron spectroscopy（XPS）.The above experimental results showed that the main component of FC is Al₂O₃,and NZVI is successfully and uniformly loaded on the FC surface and in the channels in the shape of smaller spherical nanoparticles and polygonal particles.NZVI possesses a typical core-shell structure with Fe₂O₃ and Fe₃O₄ as shell and Fe⁰ as the core.The FC with a porosity of 80.27%can provide more micro-vias for attaching more NZVI particles,and the total iron loading on the ceramic support is approximately 20.66mg/g.（2）The results of dynamic adsorption experiments on Pb（II）by NZVI/FC showed the following points.When the p H of solution was below 2,the removal efficiency of Pb（II）on NZVI/FC decreased gradually with the decrease of p H.When the p H of solution was high above 7,the removal efficiency of Pb（II）on NZVI/FC decreased gradually with the increase of p H.The obtained Pb（II）removal efficiency was relatively stable over a wide p H which ranged from 2 to 7.In the initial stage of reaction,the removal efficiency of Pb（II）on NZVI/FC stabilized at about 99.9%with the increase of the initial concentration of the solution,while it would declined,when the adsorption capacity of the adsorbent beyond the critical value.With the increase of the flow rate of the solution,the removal efficiency would generally maintain at 100%when the initial concentration at 80 ppm.And the removal efficiency could reach 100%after 10 minutes when the initial concentration at 700 ppm.The adsorption kinetics for Pb（II）removal on NZVI/FC confirmed chemical sorption as the rate-limiting step of adsorption mechanisms.Moreover,the adsorption procedure affected by the diffusion of the fluid film diffusion in the initial stage,and then determined by the intraparticle diffusion.Thermodynamic studies of the adsorption for Pb（II）indicated that these processes are endothermic,spontaneous and naturally favorable.（3）After degradation of Pb（II）,the surface of NZVI/FC was changed to irregular sheet-like nanoparticles,and its main component lepidocrocite（γ-Fe OOH）.Furthermore,elemental analysis indicated that Pb（II）was adsorbed and fixed on the surface of NZVI/FC.During the adsorption process,Pb（II）were removed by the ion exchange reaction with Na+and surface complexation and microprecipitation such as[Pb SO₄·2Pb CO3·Pb（OH）₂]and Pb₃O₄.In this study,the mechanism of adsorption of Pb（II）by the NZVI/FC composite material were revealed,and the methods of adsorption kinetics,adsorption thermodynamics,and material characterization were established.It was of great potential to further optimizing the material for removing heavy metal pollutants in sewage treatment.