Adsorption Behavior And Mechanism Of Phosphate By Resin-based Metal Composites

The discharge of phosphate has caused pollution problems such as eutrophication,and has seriously affected the ecological balance and drinking water safety.Nanocomposite adsorbents have been widely used in water treatment.In this study,three types of resin-based metal composite materials were synthesized:iron-loaded adsorption resin,lanthanum-loaded and FeOOH-loaded anion exchange resin.Phosphate was used as the adsorbate,and the effects of specific surface area,pore size,functional groups,and metal nanoparticles on the adsorption behavior were investigated.(1)The post-crosslinking reaction is an effective way to adjust the specific surface area.Different Friedel-Crafts reaction time can prepare adsorption resins with specific surface area.The higher the degree of post-crosslinking resulted in the larger the specific surface area of the resin,but the grafting of functional groups and available adsorption sites would reduce.The increase of the specific surface area does not improve the adsorption performance of phosphate.However,the small pore size can increase the exposure of the surface hydroxyl groups of iron particles through the size limitation.The interference sequence of coexisting anions on the adsorption capacity is:SO₄^2->Cl^->NO₃^-;the isothermal adsorption conforms to the Freundlich model,and the adsorption kinetics conforms to the pseudo-second-order kinetic model.(2)Electrostatic interaction is the main driving force for resin-based metal nanocomposites to capture phosphate,and the content of quaternary amine groups is directly related to the strength of electrostatic interaction.During the suspension polymerization,the active chloromethyl content was adjusted by controlling the dosage of 4-vinylbenzyl chloride,and then composite adsorbents with different quaternary amine contents were prepared.The loading of nanoparticles is positively correlated with the content of quaternary amine groups,and lanthanum hydroxide is transformed from needle-like nanoparticles to elliptical agglomerations.The quaternary amine group binds to the phosphate through electrostatic attraction,and the Donnan membrane effect enriches the phosphate to the surface of the adsorbent,which promotes the binding of the adsorbate to other adsorption sites.When the chlorine content of the anion exchange resin consumes 40.52%,the amount of quaternary amine groups reaches the maximum.It can be considered that the optimization of the quaternary amine groups(electrostatic interaction)on the resin reaches the optimal situation.(3)The preparation of FeOOH/anion exchange resin composite material(Fe/900)by ethylene glycol solvent heat-tight sealing method can improve the adsorption utilization rate of metal sites.Compared with the reported composite materials prepared by alkaline precipitation method,Fe/900 shows excellent performance(high adsorption capacity(especially in the presence of excessive interfering anions),high adsorption selectivity and long-term operation of adsorption-desorption cycle),when the iron content is 4.11%,the adsorption capacity of the composite material can reach 19.05mg/g(removal rate 95.25%).Studies have shown that the glycol solvothermal method can significantly increase the contribution of FeOOH sites in the phosphate adsorption process,and Fe(III)-OH is the main effective species for phosphate adsorption.Too long solvothermal reaction time will bring about side effects such as decomposition of carrier quaternary amine group,Fe(III)reduction and nano-agglomeration.The glycol solvothermal method will promote the application of nanocomposite adsorbents in water remediation,responding to the concept of sustainable development and high requirements for phosphorus removal and recycling.