Adsorption Of Hexavalent Chromium On Magnetic Chitosan Composite Microspheres

Chromium is a necessary element for human and animal growth.Chromium and its compounds are also important materials in leather industry,textile industry and electroplating industry.However,due to the low utilization rate,chromium pollution in water is serious in recent years.Chromium pollution will cause great damage to human body,animals and plants.In order to solve the hazards of chromium pollution,the traditional methods of treating chromium mainly include physical method,chemical method and physical chemical method.At present,the most economical way to treat chrome tanning wastewater is chemical precipitation method.The precipitator usually uses magnesium oxide or sodium hydroxide and other alkaline substances.But chemical precipitation method has many drawbacks.First,chemical precipitation takes a long time and usually takes more than two days.Second,a large number of high-concentration chromium-containing sludge will be produced.Landfill method is the main method to treat sludge.Landfill sludge will not only expose the sludge.Chromium???is oxidized to chromium?VI?rapidly in natural environment and can not be recovered from sludge,resulting in a great waste of chromium resources.Therefore,it is necessary to find a method to remove chromium?VI?quickly and recover chromium?VI?.Among many methods,adsorption has attracted much attention because of its wide adaptability,easy operation,easy regeneration and insensitivity to toxic substances.In recent years,magnetic nanoparticles have become an ideal carrier for various adsorbents to purify chromium-containing wastewater.Firstly,the combination of adsorbents and magnetic nanoparticles can produce a large specific surface area,thus increasing the adsorption capacity of chromium and accelerating the reaction speed.Secondly,the magnetic adsorbent can be separated from the treated waste water by external magnets,so that chromium can be recovered.Therefore,the magnetic composite microspheres of 4-vinylpyridine chitosan?VMCPs?were prepared by the combination of 4-vinylpyridine-grafted chitosan and magnetic Fe₃O₄ nanoparticles.The magnetic adsorbent has the advantages of fast removal of chromium?VI?,easy separation from treated waste water and reusability.The effects of pH,adsorption time and initial concentration on the removal of chromium?VI?from wastewater by nano-absorbers were studied.The adsorption kinetics and isotherm equation were fitted by the model.The reuse ability of poly?4-vinylpyridine?chitosan magnetic composite microspheres?VMCPs?was also discussed.The results show that the removal of chromium?VI?from wastewater by magnetic composite microspheres of poly?4-vinylpyridine?chitosan?VMCPs?is remarkable.The main contents and conclusions are as follows:?1?Synthesis of Fe₃O₄ magnetic nanoparticles.Fe₃O₄ nanoparticles were synthesized by coprecipitation of Fe???and Fe???under alkaline conditions.?2?Preparation of Fe₃O₄@SiO₂ nanoparticles.Fe₃O₄@SiO2 nanoparticles were prepared by coating SiO₂ on the surface of Fe₃O₄ nanoparticles prepared in the first step by hydrolysis of Na₂SiO₃.?3?Preparation of magnetic chitosan microspheres?MCPs?.Magnetic chitosan microspheres?MCPs?were prepared by inverse emulsion crosslinking and glutaraldehyde?GLA?as crosslinking agent.?4?Preparation of poly?4-vinylpyridine?chitosan magnetic microspheres?VMCPs?.The monomer was grafted onto magnetic chitosan microspheres?MCPs?.Poly?4-vinylpyridine?chitosan magnetic microspheres?VMCPs?were prepared by free radical initiated graft copolymerization using potassium persulfate?KPS?as initiator.?5?Characterization of VMCPs.Fourier transform infrared spectroscopy?FTIR?,scanning electron microscopy?SEM?,thermogravimetric analysis?TG?,saturation magnetization?VSM?,Zeta potential,particle size and moisture content were used to study the functional group structure,surface morphology and thermal stability of the microspheres,and to determine whether the magnetic particles were successfully coated by chitosan and whether 4-vinylpyridine was grafted.?6?Drawing Cr???Standard Curve.In order to determine the concentration of Cr???in solution,and to study the adsorption capacity and adsorption rate of adsorbent for Cr???.This experiment was prepared to use diphenylcarbazide spectrophotometry to detect chromium.?7?Application of VMCPs.The effects of initial pH,initial concentration and adsorption time on the adsorption of Cr???on polymer-grafted magnetic chitosan microspheres were studied.?8?Mechanism of Adsorption of Cr???by VMCPs.The adsorption isotherms and kinetics data were analyzed by several common models,and the mechanism between VMCPs and Cr???was analyzed by using several commonly used kinetics or adsorption isotherm models.?9?Research of VMCPs'recycling.The method used in this experiment is different from other methods in that it is reused.That is to say,the recycling performance of VMCPs was studied through the adsorption-desorption cycle experiment of Cr???.