Application Of Layered Double Hydroxides Based Hydrogels For Removal Of Heavy Metals From Aqueous Solution

Various approaches have been developed for the abatement of heavy metal from aqueous solution.Adsorption is attracted increasing attention due to its low cost,easy operation,high efficiency,no secondary pollution,recyclable of adsorbent.And looking for adsorbent with low price,easy separation and good reusability has become current research focus.The adsorbents are usually powder,and they are difficult to separate and recycle.Then the materials with spherical and bulk form could make up for these disadvantages.In this paper,two kinds of hydrogel microspheres based on layered double hydroxides?LDHs?were successfully synthesized.The adsorption performance,mechanisms and practical application were studied by batch equilibrium experiment,dynamic column experiment,adsorption regeneration experiment and various characterization methods.The experimental results were as follows:?1?The magnetic alginate microsphere of Fe₃O₄/MgAl-LDH?Fe₃O₄/LDH-AM?was prepared by immobilizing the Fe₃O₄/LDH with calcium alginate?CA?and was used to remove Cd²⁺,Pb²⁺,and Cu²⁺from aqueous solutions.The obtained Fe₃O₄/LDH-AM was characterized by X-ray diffraction?XRD?,Fourier transform infrared spectroscopy?FTIR?,Scanning electron microscopy?SEM?,Energy dispersive spectroscopy?EDS?,X-ray photoelectron spectroscopy?XPS?,and Brunauer-Emmett-Teller?BET?surface area determination.The results indicated that the surface groups of the alginate and LDH were retained and so was the crystal structure in the alginate microsphere.The adsorption performance of the Fe₃O₄/LDH-AM for Cd²⁺,Pb²⁺,and Cu²⁺in aqueous solutions was evaluated by batch and column adsorption experiments.The effects of adsorption conditions,kinetics,isotherms,mechanisms,and potential applications were investigated.The adsorption kinetic data conformed to the pseudo-second-order kinetic equation,and the isotherm data fit well with the Freundlich and Langmuir isotherm models.The adsorption mechanism of Cd²⁺,Pb²⁺,and Cu²⁺by Fe₃O₄/LDH-AM entailed surface complexation and precipitation of carbonate.The experimental breakthrough curves were correlated with the Thomas model.Moreover,the Fe₃O₄/LDH-AM displayed superior regeneration and reusability.These results suggest that the Fe₃O₄/LDH-AM is an efficient adsorbent for the removal of heavy metals and can be effectively employed in practical applications.?2?The polyethylimide/LDH?PEI/LDH?was synthesized by crosslinking method and it fixed with calcium alginate to form PEI/LDH calcium alginate microspheres?PEI/LDH-AM?.It was characterized by XRD,FTIR and XPS techniques.The results showed that PEI/LDH-AM had variety of functional groups?hydroxyl,carboxyl,and amino?.The adsorption performance and practical application of PEI/LDH-AM for Cd²⁺,Pb²⁺and Cu²⁺in aqueous solution were studied by batch and column experiments.The adsorption kinetic data fitted with the pseudo-second-order kinetic equation,and the adsorption isotherm data fitted with the Langmuir adsorption model.The adsorption mechanisms mainly included the complexation reaction with various functional groups and the formation of carbonate precipitation.In the dynamic column adsorption experiment,the experimental data conformed to the Thomas model.Moreover,the regeneration performance of PEI/LDH-AM was good,which could be reused for at least five times.These results show that Fe₃O₄/LDH-AM and PEI/LDH-AM were efficient for heavy metal removal from aqueous solution.They were easy to be separated,reused,and can be effectively applied in practical applications.