| The pollutants contained in sediment was released as a result of riverway excavation and dredging during river treatment,which would cause secondary pollution to the water environment.Among all the pollutants,the heavy metals in the sediment caused a particularly severe contamination.Therefore,how to efficiently remove heavy metals released from sediment into water body during river treatment has become an important subject in the field of water restoration.The main research works included: magnetic adsorption composites wereprepared and the synthesis conditions were optimized,the corresponding performances and parameters of materials were discussed.The release property of heavy metals in sediment was revealed.The adsorption and separation of heavy metals from water environment were also conducted and the removal efficiency was studied.The regeneration performance of adsorption composites was also tested.Results indicated that three magnetic adsorption composites were prepared by means ofembedding and crosslinking methods by integrating sodium alginate(SA),magnetic Fe3O4 nanoparticles and functional adsorption monomer with cross linking agent(PVP).The effect of materials composition and content on the adsorption performance of magnetic materials was analyzed by orthogonal experiment,the surface morphology and crystal structure of three magnetic materials including without addition monomer composite(magnetic Fe3O4/SA/PVP/calcium gel composite,MSPC),addition of diatomite composite(magnetic Fe3O4 /SA/diatomite gel composite,MSDC),and addition of activated carbon composite(magnetic Fe3O4/SA/active carbon gel composite,MSAC)were characterized.The basic composition of the magnetic composites(SA,PVP,Fe3O4)had a great effect on the adsorption-crosslinking and magnetic response performance.All these three materials showed abundant pores which formed network structure,and hadthe paramagnetism with the maximum magnetization intensity of 7.92 emu/g which enabled it the better separation performance with external magnetic field application.The addition of gel materials could improve the mechanical strength and tenacity of adsorbent,the internal structure of materials could be maintained after stretching and stirring,which played a key role in maintaining the apparent integrity and prolonged the service life.The effect of external interferences on the heavy metals release in sediment were simulated in a cycling tank,the mechanism and adsorption/desorption kinetics of the heavy metals in sediment were also studied.Experimental results showed that the releaseamount of heavy metals was accelerated at higher temperature and salt concentration,acidic water environment and larger water disturbance.The adsorption process of heavy metals in sediment was in line with the secondary reaction kinetics,and the Elovich equation could well explain the adsorption process of heavy metals in sediment.The adsorption of Cd2+ in water environment by MSPC was studied,and the adsorption process was analyzed with isothermal adsorption,kinetics and thermodynamics.The result indicated p H 6~7 favored the removal of Cd2+ in water environment,and the time to adsorption equilibrium was 80min-120 min.Higher than 65% of Cd2+ removal was obtainedwhen the concentration of Cd2+ was 50~150mg/L mg/L in water environment.The adsorption of heavy metals with MSPC was according with Langmuir isotherm,and the pseudo-second order mode could well describe the adsorption process with R2>0.96,thermodynamics analysis determined the chemical adsorption process.Additionally,the maximum adsorption capacity of synthesized adsorbents was 50% of that for the original materials after using 3~5 time repeatedly,indicating the better regeneration performance.The matrix sediment samples were collected from districts which were contaminated by heavy metals.After analyzing the pollution of heavy metals in water environment in cold regions,the tested water-sediments mixture were prepared.The magnetic adsorption composites was used to adsorb and separate heavy metals,and the optimized technological parameter were obtained for the different concentrations of heavy metals in sediment.The optimal condition for magnetic separation was magnetic field intensity 1.1 T,contacting time 4 hours,and stirring speed 160 r/min.This study could provide a feasible method for the released pollutants removal,especially heavy metals in river body during sediment dredging.This method could be accomplished by adding magnetic composite adsorbents to adsorb heavy metals in the water body.After separating these adsorbents by magnetic method,the adsorbent composites could be reused after desorption treatment. |
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