Study On The Efficacy And Mechanism Of Composite Modified Nano-Zero Valent Iron In Remediation Of Groundwater Polluted By Hexavalent Chromium And Trichloroethylene

With the rapid development of my country’s industry,the problem of groundwater pollution has become more and more serious,and groundwater pollution is characterized by complex types of pollution,strong persistence,and difficulty in treatment.Therefore,it is urgent to develop effective groundwater pollution remediation technologies.Hexavalent chromium(Cr(Ⅵ))and trichloroethylene(TCE)are representative pollutants in groundwater,both of which are the most frequently detected and highly toxic pollutants in groundwater.Nano-zero valent iron(n ZVI)in situ remediation is a common groundwater treatment technology at home and abroad.n ZVI has the advantages of small particle size,strong adsorption and high reactivity,which makes it have good removal ability for Cr(Ⅵ)and TCE..However,n ZVI has defects such as easy agglomeration and easy oxidation in the actual application process,which seriously affects its application performance.In order to solve the above problems,in this study,a doublemodified n ZVI-based material(CMC-OA-n ZVI)with sodium carboxymethylcellulose and sodium oxalate was prepared,and the prepared CMC-OA-n ZVI was used to remove the Cr(Ⅵ)and TCE,the efficiency,influencing factors and related mechanisms of CMC-OA-n ZVI in removing Cr(Ⅵ)and TCE in groundwater were explored through batch experiments.The specific results are as follows:(1)The influence of the preparation parameters of CMC-OA-n ZVI was investigated,and the results showed that the dosage ratio of Fe,CMC and OA during the synthesis of CMC-OA-n ZVI would have a certain influence on its application effect.When the molar ratio of :OA:CMC was 1:0.35:1,CMC-OAn ZVI had the best removal effect on Cr(Ⅵ)and TCE.The related characterization results show that CMC is successfully wrapped on the surface of n ZVI in the form of a coating layer,which prevents the formation of agglomerates between n ZVI particles;after the modification of CMC and OA,the saturation magnetization of CMC-OA-n ZVI is smaller than that of n ZVI,indicating that This modification process can effectively reduce the agglomeration of n ZVI;in addition,the introduction of OA and CMC increases the number of functional groups on the surface of n ZVI,which can promote the adsorption and removal process of pollutants;in addition,the combined modification process has a certain protective effect on n ZVI,The formation of the surface passivation layer is hindered.(2)The adsorption performance of CMC-OA-n ZVI on Cr(Ⅵ)was studied by sequencing batch static adsorption experiments.Good;the optimal dosage of CMC-OA-n ZVI is 0.5 g/L,at this time the removal rate of Cr(Ⅵ)reaches 68.5%;in addition,the reaction can reach equilibrium in a short time(120 min),The maximum adsorption capacity reached 346.61 mg/g.Common coexisting ions and HA have little effect on the adsorption process,indicating that the adsorption process is relatively stable;in addition,the Avrami kinetic model and the Langmuir and Sips isotherm adsorption models can better fit the adsorption process,indicating that CMC-OA-n ZVI has a strong effect on Cr adsorption.The adsorption of(Ⅵ)is a monolayer adsorption with multiple kinetic processes.The thermodynamic calculation and analysis show that the adsorption of Cr(Ⅵ)by CMC-OA-n ZVI is an endothermic reaction and can proceed spontaneously.(3)The adsorption performance of CMC-OA-n ZVI on TCE was studied by sequencing batch static adsorption experiments.The removal effect was the best;the reaction reached equilibrium at about 360 min,and the maximum adsorption capacity reached 26.18 mg/g.The effect of coexisting ions or HA on the adsorption capacity is low,indicating that the adsorption process has strong anti-interference ability;in addition,the Avrami kinetic model and the Freundlich and Redlich-Peterson adsorption isotherm models fit the adsorption process better,indicating that CMC The adsorption of TCE by-OA-n ZVI is a multilayer adsorption process with multiple kinetic processes.Thermodynamic analysis showed that the adsorption of TCE by CMC-OA-n ZVI was a spontaneous endothermic reaction process.(4)The mechanism of CMC-OA-n ZVI removal of Cr(Ⅵ)and TCE was analyzed,and the results showed that electrostatic attraction,reduction and co-precipitation were the key roles of Cr(Ⅵ)removal;in addition,CMC-OA-n ZVI Efficient removal of TCE was achieved by physical adsorption and reductive dechlorination.