Study On The Removal Of Heavy Metals And Phosphate From Aqueous Solution By Modified Diatomite

Nowadays,heavy metals and phosphate pollution have become a topic of worldwide concern on account of the adverse impact to ecology and humans.Adsorption can be applied to remove heavy metals and phosphate from wastewater with the merits of its simplicity and flexibility of design,greater selectivity,faster regeneration kinetics and ease of operation.Nevertheless,the key issue for the application is to find a highly effective,environmental friendly and economical adsorbent.Diatomite is regarded as an ideal adsorbent owning to the merits of low-cost,abundant and available,porosity,high permeability,thermal stability.The low adsorption capacity and difficulty in separation,however,greatly limit its application.It would be highly desirable to realize the combination of diatomite,amino functional group with complexing capacity and Fe₃O₄ which features superparamagnetism via an appropriate synthesis method.Firstly,we present amino-functionalized magnetic diatomite nanocomposite?Fe₃O₄/DTM?by loading Fe₃O₄ nanoparticles onto the raw diatomite?DTM?clay surfaces via a simple one-pot solvothermal method.The as-prepared composites were characterized by X-ray diffraction?XRD?,Fourier transform infrared spectroscopy?FTIR?,X-ray photoelectron spectroscopy?XPS?,scanning and transmission electron microscope with energy dispersive spectroscopy?SEM/TEM/EDS?,Brunner-Emmet-Teller measurements?BET?,and vibrating sample magnetometer?VSM?.The results indicated that a large amount of tiny sphical morphology?Fe₃O₄?was adhered to the entire surface of DTM with a disk-like morphology and uniform ordered porous structure.The mesoporous materials?Fe₃O₄/DTM?was successfully synthesized and possessed high crystallinity and rich functional groups?hydroxyl and amino groups?.The larger surface area,pore volume and pore size of Fe₃O₄?50.3 m2/g,0.2408 cm3/g and 8.7 nm?can provide more active sites to adsorb metal ions and phosphate.The saturation magnetization values?26.89 emu/g?elucidated the strong magnetism of Fe₃O₄/DTM,which is sufficient for the separation of Fe₃O₄/DTM from the suspension.Secondly,the adsorption behaviors,properties and mechanisms of Fe₃O₄/DTM for Pb²⁺,Cd²⁺and Cu²⁺were evaluated via a wide variety of adsorption conditions,kinetic,isothermmodels and characterization methods.The results demonstrated that Fe₃O₄/DTM exhibited significantly enhanced adsorption capacity than DTM and it can quickly and effectively remove the metal ions within 20 min.There was a negligible effect on heavy metals adsorption by the existence of Na+?K+?Mg²⁺?Ca²⁺.The adsorption kinetics followed the pseudo-second-order model and the interior diffusion was dominant rate-determining step for the whole diffusion process.The Langmuir and Temkin model can agree well with the equilibrium data,indicating that the adsorption of metal ions onto Fe₃O₄/DTM was a favourable,homogeneous monolayer chemical adsorption process.The maximum adsorption amounts of Fe₃O₄/DTM for Pb²⁺,Cd²⁺and Cu²⁺were 51.65,42.17 and 7.12 mg/g,respectively.The analyses of Zeta potential and XPS validated the adsorption mechanisms of electrostatic interaction,complexation and ions exchange between Pb²⁺,Cd²⁺,Cu²⁺and Fe₃O₄/DTM.Besides,the adsorbent Fe₃O₄/DTM could be quickly separated using a magnet and the adsorbate ions can be easily recovered by acid treatment after adsorption.Finally,Fe₃O₄/DTM was used as adsorbent for removal of phosphate from aqueous solution.The optimal adsorption conditions,properties and mechanisms of phosphate on Fe₃O₄/DTM were studied in detail.The results revealed that the adsorption process was pH-dependent and reached equilibrium within 30 min.The larger adsorption capacity occurred in the acid phosphate solution and the equilibrium suspension pH fluctuated at about8.0.The adsorption kinetics followed the pseudo-second-order kinetic equation and the rate-limiting step was influenced by intra-particle diffusion.The isotherm data was well described by the Langmuir model and the maximum equilibrium adsorption capacity of Fe₃O₄/DTM was 11.89 mg/g.The adsorption mechanisms of phosphate were ascribed to the electrostatic attraction and ligand exchange.In conclusion,Fe₃O₄/DTM can be readily synthesized by abundant and low-cost diatomite.The as-prepared composites endow superior adsorption performance,reusability and separability,which are an ideal adsorbent for removal of heavy metals and phosphate from aqueous solution.Hence,it implies a great potential for application in heavy metals and phosphate uptake from wastewater.