Removal Of Chromium Hexavalent From Water By Modification Of Peg Stabilized Nano Zero-valent Iron Composite

With the rapid development of modern industry and agriculture,hexavalent chromium(Cr(?))has been widely used in many fields such as leather,steel,electroplating,mining and wood anticorrosion.Cr(?)is highly water-soluble and mobile in surface water,which increases the chance of contact with humans and leads to carcinogenicity and mutagenicity.Therefore,it is urgent to find green and economic Cr(?)treatment technology.At present,many Cr(?)removal materials based on nanometer zero-valent iron(nZVI)have been reported in the literature.nZVI is considered as a good adsorbent for environmental pollution remediation due to its simple preparation,low cost and good reducibility.However,nZVI also has some disadvantages,such as easy agglomeration and oxidation,which greatly reduce the removal rate of Cr(?).So it is necessary to modify nZVI to overcome these defects.In view of the above problems,this paper successfully prepared modified nZVI by liquid phase reduction method,and three composite adsorption materials were used to treat simulated Cr(?)wastewater.The treatment performance of these composite adsorbents was evaluated,and the influencing factors and reaction mechanism of Cr(?)removal were investigated.The main research contents and conclusions are as follows:1?Nickel-doped polyethylene glycol stabilized zero-valent iron nanoparticles(Ni/Fe-PEG)was prepared by liquid phase reduction method,and it was used in the treatment of Cr(?)solution for the first time.The optimum conditions for Ni/Fe-PEG treatment of Cr(?)are as follows:dosage 0.6 g·L^-1,initial p H 5.0 and initial Cr(?)concentration 50 mg·L^-1.The removal rate of Cr(?)and equilibrium adsorption capacity of Ni/Fe-PEG can reach 99%and 128.47 mg·g^-1,respectively.The removal of Cr(?)by Ni/Fe-PEG can be summarized as adsorption,reduction and coprecipitation.First,Cr(?)is adsorbed on the surface of Ni/Fe-PEG,and then it is reduced to Cr(III)by nZVI,finally,Cr(III)and Fe(III)form coprecipitation attached to the surface of Ni/Fe-PEG.PEG can disperse nZVI,while Ni can weaken nZVI oxidation and promote Cr(?)reduction.2?D201 resin supported polyethylene glycol stabilized nZVI(PEG-nZVI/D201)was prepared by liquid phase reduction method.When PEG-nZVI/D201 dosage was 1.0 g·L^-1,Cr(?)concentration was 50 mg·L^-1 and initial p H was 5.0,the removal rate of Cr(?)and the equilibrium adsorption capacity of PEG-NZVI/D201 reached 91.54%and 123.96 mg·g^-1,respectively.The Langmuir model describes the adsorption of Cr(?)on PEG-nZVI/D201,the thermodynamic parameters show that the adsorption is spontaneous and endothermic.The mechanism of Cr(?)removal by PEG-nZVI/D201 is summarized as follows:first,protic PEG-nZVI/D201 adsorbed Cr(?)by electrostatic attraction,and then nZVI reduced most of Cr(?)to Cr(III)through its strong reductive property,finally,Cr(III)co-precipitated with Fe(III)generated by nZVI oxidation to form Cr _XFe_1-X(OH)₃.3?Sodium dodecylbenzene sulfonate modified polyethylene glycol(PEG)stabilized nZVI(PS-nZVI)was prepared by liquid phase reduction method.The static adsorption experiments of PS-nZVI on Cr(?)showed that when the dosage of PS-nZVI was 1.0 g·L^-1,the initial concentration of Cr(?)was 50 mg·L^-1,the p H value was 5.5,the removal rate of Cr(?)and equilibrium adsorption capacity of PS-nZVI were 92%and 122.3 mg·g^-1,respectively.The adsorption process can be described by quasi-second-order kinetics and Langmuir isothermal model,it is characterized by spontaneous endothermy and monolayer surface chemisorption.The mechanism of PS-nZVI removal of Cr(?)is as follows:Cr(?)is adsorbed on the surface of PS-nZVI by electrostatic attraction,and then nZVI and Fe(II)reduce Cr(?)to Cr(III),and are themselves oxidized to Fe(III),Cr(III)and Fe(III)forms Cr _XFe_1-X(OH)₃ or Cr _XFe_1-XOOH are attached to the PS-nZVI surface.4?Ni/Fe-PEG,PEG-nZVI/D201 and PS-nZVI composite materials are compared in terms of size,adsorption equilibrium time,maximum adsorption capacity and cost estimation.It is found that Ni/Fe-PEG system has the most application prospect,which can provide a new idea for the development of nZVI composites in the future.