| In recent years,with the rapid development of social production activities and industry,nitrate pollution has been widespread at home and abroad,posing a great threat to people’s health and ecological environment.Nanometer zero-valent iron(nZVI)has been widely used in the removal of nitrate in water due to its large specific surface area,strong reducing activity,low price and friendly environment.However,there are still some problems to be solved in nZVI technology :(1)nanometer zero-valent iron is extremely easy to be oxidized,and a dense oxide film is formed on its surface,which hinders the contact between zero-valent iron and pollutants,making zero-valent iron unable to react with pollutants further and reducing the utilization rate of zero-valent iron;(2)nanometer zero-valent iron particles have a tendency of spontaneous agglomeration,which reduces the adsorption sites of nanometer zero-valent iron particles and reduces their reactivity.Therefore,how to inhibit the agglomeration of nano-zero-valent iron and improve the reduction efficiency of nano-zero-valent iron particles is an important problem to be solved urgently.This paper by pyridyl chelating resin(DOW n)as the carrier,the preparation of load type nano iron copper double metal composite materials,by using scanning electron microscope(SEM),energy spectrum analysis(SEM,EDS),X-ray photoelectron spectroscopy(XPS)and the projection electron microscope(TEM)characterization analysis method to analyze the structure and composition of the material,to study the mechanism of material reduction of nitrate in water,systematically discusses the water quality conditions on the load type nano iron copper double metal composite material impact on the water nitrate reduction mechanism,and studies the material removal mechanisms of nitrate and phosphate in water synchronization.On this basis,the stability of the material and its application in practical water were discussed.The main research contents and conclusions are as follows:(1)reduction characteristics of supported nano-iron/copper bimetallic composites to nitrates.The results of SEM-EDS and TEM show that DOW3 N is a good carrier of metal nanoparticles and can obtain iron-copper nanoparticles with uniform distribution.The resin can reduce the agglomeration of fe-cu bimetallic nanoparticles and improve the stability of nanoparticles.XPS results show that the composite has the metal morphology of zero-valent iron and zero-valent copper,but the metal morphology containing partial oxidation state may be generated in the process of sample preparation and preservation.With the increase of the copper load,the reduction efficiency of the material to nitrates was improved,but with the continuous increase of the copper load,the reduction efficiency of nitrates decreased.(2)the influence mechanism of water quality conditions on the reduction of nitrate by loaded nanoiron/copper bimetallic composites.The nitrate concentration had little effect on the removal rate,but as the initial concentration of nitrate increased,the removal rate of nano-fe /Cu composite became lower and lower.PH has a great influence on the removal of nitrate in composites,and low pH is more conducive to the reduction reaction.DO reacts with nanometer zero-valent iron,thus affecting the removal efficiency of nanometer zero-valent iron on pollutants.Sulfate,chloride ion,phosphate and bicarbonate ions such as competition and humic acid are to some extent,prevent nano zero-valent iron on nitrate removal,perhaps the main cause is competition with ions,humic acid and nitrate nanometer zero-valent iron on the activity level,on the other hand,the precipitation was adsorbed in the nanocomposites,suppresses the nanometer iron copper corrosion of metal and electron transfer,thus affecting nitrate removal.(3)supported nano-iron/copper bimetallic composites remove nitrate and phosphate in water simultaneously.The synchronous removal mechanism of nitric acid and phosphate in water by d-fe /Cu supported nano-fe /Ni bimetallic composites was studied.The results showed that d-fe /Ni and d-fe /Cu had high nitrate reduction efficiency and phosphorus removal efficiency.The removal rates of nitrate by d-fe /Ni and d-fe /Cu were 98.7% and 95.5%,respectively.Ammonia was the main product of d-fe /Ni reduced nitrate,while nitrite and ammonia were the reduced products of dfe /Cu.The removal efficiency of d-fe /Cu and d-fe /Ni was 99% and 93%,respectively.The removal mechanism of phosphate mainly includes adsorption,co-precipitation and the adsorption of phosphate by polymer ligand(PLE)formed in the oxidation process of the material.When nitrate and phosphate coexist,d-fe /Cu and d-fe /Ni can achieve simultaneous removal of nitrate and phosphate.In the presence of nitrate,the removal of phosphate can be promoted.When phosphate exists,it has an inhibitory effect on the removal of nitrate,but d-fe /Cu has little effect on the removal of nitrate,while d-fe /Ni has a greater effect on the removal of nitrate.(4)stability of loaded nano-iron/copper bimetallic composites and their applications in practical water bodies.The heavy metal Cu was almost lost in the process of regeneration.After reloading the metallic iron,the material was reduced with sodium borohydride.The experimental results showed that the removal rate of nitric acid could still reach 97.41% after the material was reused for five times.The material was used to remove nitrate in secondary biochemical effluent of sewage treatment plant,and the removal rate was 29.40%. |
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