Studies On Preparation Of Magnetic Chitosan Particles And Their Adsorption Of Typical Heavy Metal Ions And Magnetic Recovery

With the rapid development of industry,limited water resources have been seriously polluted.Therein,heavy metal pollution has been one of the urgent problems to be solved.Adsorption method is a simple and efficient method for the treatment of heavy metal pollution in water.Among various adsorbents,the magnetic chitosan adsorbent,as a kind of prospective adsorbent,has both the good adsorption capacity of chitosan and the recyclable property of magnetic materials.At present,the study of magnetic chitosan for adsorption of heavy metal ions was focus on improving the adsorption capacity and selectivity.There are lacking the research about the stability,comprehensive evaluation and magnetic recovery of magnetic chitosan beads.These three aspects were studied in the dissertation.The specific contents are as follows.Firstly,the stability of magnetic chitosan was studied.Magnetic chitosan beads synthesized through common embedding method and crosslinked with glutaraldehyde were studied for the adsorption of Cu²⁺in aqueous solution.Magnetic chitosan beads were investigated by means of hysteresis curve,thermo-magnetizationcurve,TGA,FTIR and XRD.Kinetic,isothermal and thermodynamic studies were applied to investigate the adsorption of Cu²⁺by magnetic chitosan beads.Adsorption properties andthe stability of magnetic chitosan beads including adsorption capacity?Q?and saturated magnetization?M_s?stability in various conditions were investigated.Simultaneously,the FTIR and XRD were utilized to further analyze the change of magnetic chitosan beads in stability studies.The results suggested that magnetic chitosan beads showed good stability without significant loss in Q and M_s after regeneration of five sequential cycles.Magnetic chitosan beads presented excellent storage stability while stored in drying vessel for ten months.For thermal stability,the Q and M_s of magnetic chitosan beads were presented similar variation after heated under atmosphere and vacuumat different temperature for 30 h.The Q of changed little after heated at 50 and 100°C,and decreased sharply at 150 and 200°C.The magnetization was stable at lower temperature range?50-150°C?and increased slightly at 200°C.Different magnetic fields had little effect on the stability of magnetic chitosan beads.Secondly,there was not a standard or evaluation method for evaluating the overall performance of various magnetic chitosan materials.For comprehensively evaluating the performance of magnetic chitosan beads,the evaluation models were established.The adsorption recovery index?ARI,ARI=_t^Q?was presented by the Q and recovery time?t?obtained from 98%recovery rate.The magnetic chitosan beads with higher value of ARI are better.Secondly,a vector model was proposed combing Q and M_s,the two characteristic indexes of magnetic chitosan beads.The normalized values of Q and M_s were put into a two-dimensional coordinates.The target?1,1?has the optimum value of Q and M_s.The distance between magnetic chitosan beads and the target in the coordinate system is applied to evaluate the material.The magnetic chitosan beads nearer the target in the vector image were the better ones.Two kinds of magnetic chitosan beads were prepared with different chitosan mass ratio without modification for adsorption of metal ions with different valence(Ag⁺,Cu²⁺,Hg²⁺,Cr³⁺and Cr⁶⁺),which were applied for checking the scientificity and effectiveness of the evaluation models proposed.After the evaluation of various magnetic adsorbents,there are lacking the adsorbents with both approving magnetization and adsorption capacity in the present studies.Two kinds of magnetic chitosan materials with approving Q and high M_s were prepared.The first one was tetraethylenepentamine?TEPA?modified chitosan/CoFe₂O₄ particles.The particles were applied for comparative and competitive adsorption of Cu?II?and Pb?II?in single and bi-component aqueous solutions.The characteristics results of SEM,FTIR and XRD indicated that the adsorbent was successfully fabricated.The magnetic property results manifested that the particles with saturation magnetization value of 63.83 emu g^-1 would have a fast magnetic response.The effects of experimental parameters including contact time,pH value,initial metal ions concentration,coexisting ions and humic acid on single and bi-component adsorption were investigated.The results revealed that the adsorption kinetic was followed pseudo-second-order kinetic model.Sorption isotherms were also determined in single and bi-component solutions with different mass ratio of Cu?II?to Pb?II??Cu?II?/Pb?II??and fitted using Langmuir and Freundlich isotherm models.A better fitting for Cu?II?and Pb?II?adsorption were obtained with Langmuir model,with a maximum sorption capacity of 168.0 and 228.3 mg g^-1 for Cu?II?and Pb?II?in single component solution,139.8 and 160.2 mg g^-1 in bi-component solution?Cu?II?/Pb?II?=1:1?,respectively.The second one was poly?acrylic acid??PAA?modified high magnetic chitosan particles.The adsorbents were composed of high magnetic core?CoFe?and then the magnetic core werecoated with silica layers.Finally,chitosan were coated and modified by PAA.The properties of the adsorbent were characterized by SEM,FTIR,X-ray diffraction and magnetization.The charaterization indicated that the particles were synthesized successfully.The particle held excellent saturation magnetization?M_s?of 118.91 emu g^-1.Experiments were carried out to investigate adsorption kinetics,adsorption isotherm,the effect of solution pH values on the removal of Cu²⁺,desorption and resuability study and comparison with other adsorbents.Kinetic data were well fitted by a pseudo second-order model.Langmuir model agrees very well with experimental data and its calculated maximum monolayer adsorption capacity was 234.1 mg g^-1.Furthermore,the loaded adsorbent could be regeneratedby EDTA solution.After the adsorption process is finished,the recovery and reuse of adsorbents could reduce secondary pollution and save resources.The recovery model was established by permanent magnets.Different magnet arrangements were applied,which were bottom recovery model and both sides recovery mode.The two models were a magnet placed on the bottom of the magnetic recovery pool and two magnets placed on both sides of the magnetic recovery pool,respectively.The recovery efficiency equation was deduced by the force analysis of the magnetic chitosan particles in the magnetic field.Then,the magnetic chitosan with chitosan mass ratio of0.3 prepared by embedding and chemical precipitation methods,amine modified chitosan/CoFe₂O₄ and PAA modified high magnetic chitosan particles were applied for magnetic recovery experiments with different velocity.The recovery efficiency of PAA modified high magnetic chitosan particles obtained from the two recovery models was the best among the four kinds of magnetic chitosan particles in both recovery models,and the recovery efficiencies were both 0.99,when their velocity entering the magnetic recovery pool was 0.003 m s^-1.The recovery experimental efficiency was compared with that calcuated from the recovery efficiency equation.The results show that there are some differences between the experimental and theoretical recovery efficiency,the correction factor is added to the recovery efficiency equation by dichotomy.Finally,a more realistic recovery efficiency equation is obtained.The results of the study provide a theoretical and experimental basis for the practical application of magnetic adsorbent technology.