Study On The Preparation, Modification And Adsorption Behavior Of Al-doped Magadiite

Water pollution control is an important part of environmental and ecological protection.Because of the complex components of water pollution and the wide geographical scope of pollution,water pollution control has been a hot topic in the field of environmental research.The problem of heavy metal pollution caused by the rapid development of industry and agriculture has aroused people's attention.For example,heavy metal substances containing mercury,cadmium,lead,nickel and other heavy metals are discharged into the water environment without effective treatment,which will seriously damage the ecology and even endanger human health.Therefore,it must be strictly controlled.Among the various technologies for the treatment of water pollution,adsorption method is paid much attention by researchers at home and abroad because of its low cost and easy control.The core technology of adsorption method is the performance of adsorption materials.Mag is a kind of sodium polysilicate hydrates,which is pure and well-crystallied and can be synthesized in the laboratory with good biocompatibility and non-toxic.The lamellas is a tetrahedron composed only of silicon and oxygen elements,and there are no easily hydrolyzed elements such as magnesium and aluminum in the interlamellar and have good acid resistance and thermal stability;the lamellas have good expansibility.It is easy to make small proton and large molecular matter enter the interlayer through ion exchange.The interlayer cation exchange capacity is better than that of montmorillonite,kaolin and other traditional clay adsorption materials.The lamellas surface is rich in silica hydroxyl groups,and the lamellas element components have adjustable properties,which provides the possibility for the modification of lamellas elements doping and surface properties.Hence,modification of Magadiite can obtain water treatment adsorbent materials with excellent properties.This thesis is based on the Mag modification preparation and its adsorption behavior Pb²⁺?Hg²⁺in water,to find high performance adsorbent materials suitable for wastewater treatment with heavy metal ions,and to determine the preparation experimental process.The main research contents and results are listed as follows:?1?By regulating different doping ratios of Al elements,the trivalent Al atoms were introduced into the tetrahedral silicon and oxygen framework,and the tetravalent Si atoms were successfully isomorphous replacement to prepared Al_xMag?x=480,240,120?of the Al-doped series.The crystal shape,morphology,composition and structure of Al_xMag were systematically investigated by XRD,FT-IR,SEM,BET and NMR.The results showed morphology of Al_xMag was rose-like and interlayer spacing was 1.56 nm.and the Al₂₄₀Mag with highest surface silicon hydroxyl density as well as the zero charge of point(p H_pzc)values of Mag and Al_xMag.?2?The study of adsorption behavior of Pb²⁺solution by Al_xMag is to investigate the influence on adsorption effect of Pb²⁺from solution p H value,adsorption time,adsorption kinetics,adsorption isotherm and adsorption rate model.The experimental results showed that the best experimental conditions for the removal of Pb²⁺were:the removal of the initial concentration C₀ of Pb²⁺solution was 100mg L^-1 by Al₂₄₀Mag when the adsorption solution p H is 3.0,the feed ratio is 1.0 g?L^-1,and the adsorption time is 480 min,the adsorption rate and adsorption capacity are 94.7%and 94.1mg?g^-1,respectively;the adsorption mechanism of Al_xMag on Pb²⁺has the co-existence of ion exchange and surface complexation,and has both physical and chemical adsorption.The Pseudo-second-order kinetic model and the Langmuir model can better describe the adsorption process of Pb²⁺by Al_xMag,the entire adsorption behavior of Pb²⁺was dominated by intraparticle diffusion.?3?The novel APS-Al_xMag?x=480,240,120?adsorbents were fabricated by interlamellar grafting of amino groups.APS-Al_xMag were characterized by XRD,and it was found that the interlayer spacing was widened,SEM analysis showed that the morphology changed significantly,and the specific surface areas and pore volumes decreased significantly,but the average pore sizes increased and the pore sizes distribution widened.T² and T³ were the main methods of amino grafting,and the surface amino grafting density of APS-Al₂₄₀Mag was the highest,the p H_pzc values of APS-Mag and APS-Al_xMag were apparently higher than Mag and Al_xMag.?4?When the p H of the Hg²⁺solution is 5.0,feed ratio is 1.0 g?L^-1,adsorption time is 720 min,and C₀ is 10 mg?L^-1.The removal rate of Hg²⁺by APS-Al240Mag is88.8%,and the adsorption capacity is 9.4 mg?g^-1.The Pseudo-second-order kinetic model and Langmuir model are more suitable for describing the adsorption of Hg²⁺by APS-Al_xMag.Hg²⁺experiments in the selective adsorption of mixed heavy metal solutions,the selective removal rate and adsorption capacity of APS-Al₂₄₀Mag for Hg²⁺were 87.92%and 9.25 mg?g^-1,respectively,the distribution coefficient of Hg²⁺was 7.28*10³m L?g^-1 in mixed heavy metal solutions.It is proved by XPS that the complexation between the surface amino groups and Hg²⁺,indicated that the adsorption behavior was ascribed to chemical adsorption.After 5 cycles of absorption-desorption experiments,it shows that APS-Al₂₄₀Mag still has a 67.73%removal rate for Hg²⁺.