| In recent years,with the development of urbanization and industrialization,heavy metal pollution has become one of the main problems of water pollution.The adsorption method has the advantages of high efficiency,low cost,and easy operation for removing heavy metals in wastewater,and has attracted widespread attention.Among many adsorbents,magnetic nano-Fe3O4 has attracted wide attention due to its magnetic properties,easy availability,and large surface area.Chitosan molecular chain has a large number of amino and hydroxyl groups,and has good adsorption effect on heavy metal ions.As an adsorbent to treat heavy metal ions in wastewater,it is a high-yield,degradable,renewable,and environmentally-friendly adsorbent material.However,the amino group on the molecule is easily protonated under acidic conditions,and the untreated chitosan has a low specific gravity and is difficult to separate,which limits its application range.Magnetic chitosan has good magnetic properties and adsorption properties.The amino and hydroxyl groups on its surface are easy to be modified,and it is easy to be recycled after adsorption.It has been widely used.This paper successfully prepared magnetic nano-Fe3O4 and magnetic chitosan.The magnetic nano-Fe3O4 and magnetic chitosan were characterized by TEM,XRD,FT-IR,and BET.The adsorption kinetic and thermodynamic characteristics of Cr6+,Cu2+,Pb2+and Zn2+ on the magnetic nano-Fe3O4 and magnetic chitosan were studied,the effects of reaction contact time,the amount of adsorbent added,the initial concentration and temperature of the solution,and the pH of the solution on the adsorption of Cr6+,Cu2+,Pb2+and Zn2+were investigated,the adsorption effects of the two materials on heavy metal ions were compared,and the binary and ternary competitive adsorptions of heavy metal ions on the magnetic chitosan were researched.The obtained main results and knowledge are as follows:The results of TEM showed that the magnetic chitosan had a rougher surface than magnetic nano-Fe3O4,but they were all nano-levels.The results of XRD indicated that the synthesis of magnetic chitosan did not affect the crystal structure of Fe3O4.The results of FT-IR illustrated that chitosan was successfully supported on the surface of magnetic nano-Fe3O4.The results of BET indicated that the specific surface area of magnetic chitosan was larger than that of magnetic nano-Fe3O4.The above results showed that the magnetic nano-Fe3O4 and magnetic chitosan were successfully prepared.The adsorption results showed that the kinetic and thermodynamic process of the adsorptions of Cr6+,Cu2+,Pb2+ and Zn2+ on magnetic nano-Fe3O4 and magnetic chitosan could be described by the quasi-second-order kinetic adsorption model and Langmuir thermodynamic isothermal adsorption model,indicating that the adsorptions of Cr6+,Cu2+,Pb2+ and Zn2+ on magnetic nano-Fe3O4 and magnetic chitosan were mainly chemical monolayer adsorption.The maximum adsorption capacity of magnetic nano-Fe3O4 to Cr6+,Cu2+,Pb2+ and Zn2+on was 8.620,1.219,8.957,and 1.798 mg/g,respectively;the maximum adsorption capacity of magnetic chitosan to Cr6+,Cu2+,Pb2+and Zn2+on was 8.298,9.810,13.69,and 3.943 mg/g,respectively.When the initial concentrations of Cr6+,Cr2+,Pb2+ and Zn2+ increased,the equilibrium adsorption capacity increased overally;the higher the temperature of solution was,the greater the equilibrium adsorption capacity,presenting 45℃>35℃>25℃.With the increasing of the amount of magnetic nano-Fe3O4 and magnetic chitosan adsorbent,the removal rate of Cr6+,Cu2+,Pb2+and Zn2+ gradually increased,but the adsorption amount decreased.When the pH of solution was 1～2 and 1～3,respectively,the adsorption effects of magnetic nano-Fe3O4 and magnetic chitosan on Cr6+ were better.When the solution pH increased,the adsorption effects of magnetic nano-Fe3O4 magnetic chitosan on Cu2+,Pb2+and Zn2+ were relative high.By comparing the adsorption contact time,adsorption thermodynamics,initial concentration and temperature,the amount of adsorbent added and the solution pH of the adsorption of Cr6+,Cu2+,Pb2+ and Zn2+in aqueous solution by magnetic nano-Fe3O4 and magnetic chitosan,the magnetic nano-Fe3O4 had a good adsorption effect on Cr6+and Pb2+,and the magnetic chitosan had significant adsorption and removal effects on Cu2+,Pb2+ and Zn2+.The results of competitive adsorption experiments showed that in a binary competitive system,Pb2+and Zn2+inhibited Cu2+adsorption,but the effects were not significant;Cu2+inhibited Pb2+adsorption,which was greater than Zn2+;Zn2+adsorption was inhibited by Pb2+,but slightly affected by Cu2+.In the ternary competition system,the competitive adsorption order of three heavy metal ions on magnetic chitosan was Pb2+>Cu2+>Zn2+. |
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