A Study On The Fabrication Modified Magnetic Chitosan Gel Microspheres And Their Adsorption Behavior For Heavy Metals In Water

Heavy metals are difficult to be transferred and destroyed in the cycle of biomass and energy exchange.The accessible way is to change their physical and chemical forms or immobilizing heavy metal.However,heavy metal is exceedingly apt to be transferred and transformed via any common physical,chemical and biological processes in the environment and it is hard to harness this environmental problem.As a natural biomaterial with excellent adsorption properties,modification of chitosan can enhance the process of immobilization of heavy metals due to its functional group and molecular structures.In this article chitosan is used as raw material modified by cross-linking and doping.After modification,the polymorphic magnetic chitosan microsphere adsorbent was prepared by co-precipitation method.The adsorption of typical heavy metal ions(Pb²⁺,Cu²⁺,Zn²⁺)and radioactive heavy metal ions?Cs⁺?in water was studied.Finally,the dynamic adsorption experiment of modified chitosan gel microspheres as fixed bed filler was investigated.The details are as follows:?1?A novel porous magnetic chitosan gel microsphere adsorbent was prepared according to in-situ coprecipitation and ethylene glycol diglycidyl ether?EGDE?cross-linking method taking chitosan as raw material.The adsorbents were characterized by scanning electron microscopy?SEM?,transmission electron microscopy?TEM?,Fourier transform infrared spectroscopy?FTIR?and vibrating sample magnetic strength?VSM?.The results show that the adsorbent has a copious pore structure and uniformly distributed Fe₃O₄ nanoparticles with an average diameter of?2.83±0.98?nm.After the introduction of Fe₃O₄ in the adsorbent,functional groups such as hydroxyl,amino and carboxyl groups still exist.The magnetic properties of the adsorbent are good for magnetic field separation.The results in terms of adsorption properties of Pb²⁺,Cu²⁺and Zn²⁺ternary heavy metals in in-situ coprecipitation chitosan gel microspheres under different conditions show that the adsorption of three heavy metal ions by magnetic porous chitosan gel microspheres accords with quasi-secondary kinetics.The adsorption process data can be described by Langmuir isotherm adsorption equation.The adsorption of multi-component heavy metals is chemisorption,and the specific surface area is an important factor in adsorption.In the multi-adsorption system,the antagonism occurs,and the competition order of heavy metals is Pb²⁺>Cu²⁺>Zn²⁺.?2?The bentonite was fixed in the porous structure of chitosan microspheres by co-precipitation method to prepare magnetic bentonite-chitosan composite microspheres?Bn-CTS?with mixed adsorption effect to remove cesium ions?Cs⁺?from water.The composite adsorbent has a regular porous structure,and chitosan and bentonite together provide a rich binding site for effective removal of Cs⁺.The paramagnetic properties make materials easy to separate from cesium for recycling.This study optimized the chitosan/bentonite ratio,pH and contact time to achieve the best Cs⁺removal rate,discussed the adsorption kinetics and isotherms to explore the adsorption mechanism.From the results,the adsorption kinetics follows the pseudo second-order model.The adsorption equilibrium data has a high degree of fit to the Langmuir isotherm model.The maximum adsorption capacity of Bn-CTS microspheres is 57.1 mg·g^-1.In the presence of abundant cations(Li⁺,Na⁺,K⁺and Mg²⁺),the adsorbent has excellent selectivity for Cs⁺.0.1 mol·L^-1 of MgCl₂ can Cs⁺adsorbed achieve the purpose of recycling adsorbents by desorb the Cs⁺from adsorptive saturated microspheres.In general,magnetic bentonite-chitosan microspheres have great potential in dealing with radioactive waste.?3?Besides the static adsorption experiment,the adsorption kinetics experiments of cerium ions on the Bn-CTS fixed bed were carried out under the condition of difference of height of the fixed bed packing layer?5-15 cm?,the influent concentration(100-300 mg·L^-1)and the flow rate(4-20 mL·min^-1).The adsorption kinetics model of cerium ions on a fixed bed was established and the theoretical adsorption permeation curve was calculated.The results show that the high fixed bed packing layer,the influent concentration and the flow rate conditions have a significant effect on the performance of the fixed bed.According to the Thomas,BDST and Yoon-Nelson models,the theoretical adsorption transmission curve and the experimental adsorption transmission curve are in good agreement.The correlation coefficient R² of the three models is greater than 0.91.At the same time,Bn-CTS microspheres have good regeneration performance and can be reused 4 times.