The Study Of Removing Of Nitrate From Wastewater By Nano Zero Valent Iron

Water resources are closely related to the survival of mankind.In recent years,due to the rapid development of China's industry and agriculture,the pollution of nitrate has become a problem that cannot be ignored and needs to be solved urgently.Benefitting from its unique surface effect and strong reducibility,nano zero valent iron has been widely studied in the environmental field and became an effective method for removing nitrate.In this study,the nano zero valent iron was modified by metal Cu,Pd and zeolite,and the optimal catalyst preparation conditions were selected and optimized,the characterization of which provides theoretical support for its application.In this study,the nano zero valent iron was synthesized by liquid phase reduction method,and metal Cu and Pd were supported by chemical precipitation method to form bimetallic/trimetallic nanoparticles for experiments.At first the article studied the effect of Cu in the treatment of nitrate solution,which showed that loading Cu,the optimum of which is 15wt%,could accelerate the transfer of electrons and the generation of active hydrogen,thereby speeded up the progress of the reaction.The effects of initial nitrate concentration,initial pH and other factors on nitrate removal were investigated.The optimum initial nitrate concentration was determined to be 50 mg·L-1.The dosage of this experimental material was sufficient(4 g·L-1)without controlling the initial pH.In the removing of removing nitrate by Cu-nFe0 bimetallic nanoparticles,the selectivity of ammonia nitrogen is about 70%.In order to study the effect of the second type of metal which is loaded on nano zero valent iron in the nitrate removal,different types of combinations was synthesized under the condition of total metal loading in 10 wt%composed of Pd and Cu in different ratio to treat the nitrate solutiuon in a initial concentration of 50 mg·L-1.The results show that nanoparticles that containing all three metal element have the fastest rate of nitrate removal and the lowest rate of ammonia nitrogen conversion,from which the conclusion came out that it,the Pd-Cu-nFe0 trimetallic nanoparticles,was selected as the best metal modified materials.Then the effects of different Pd,Cu ratio and metal loading percentage were investigated,which showed that the best ratio of Pd and Cu ratios were 1:2 at a 15 wt%metal loading and get a lowest ammonia nitrogen conversion rate by 38%.Under the conditions above unchanged,it showed that an injection of H2 into the reaction system could significantly increase the reaction rate and help to reduce the product ammonia nitrogen conversion to a rate of 31.66%.To study the effect of zeolite in the removement of nitrate,the Cu-nFe0/(Na Y)particles prepared by ion exchange and liquid phase reduction was selected as the first type of combination,and exhibited a lower ammonia nitrogen selectivity in the nitrate removal experiments.And the effect of zeolite usage was discussed,that showed that when the amount of zeolite was 5 g,the removal rate was the fastest and reached a rate of the 98.21%at 40 minutes proving that the nitrate was completely removed,and the final conversion rate of ammonia nitrogen was only 16.16%.To study the effect of different zeolite types on nitrate removal,controlling other conditions unchanged,three other zeolite type were studied,the results show that,in all three choice,Cu-nFe0/(Na Y)presented to have the fastest removal rate,while Cu-nFe0/(Na Y)shows a lower Ammonia nitrogen selectivity(8.38%).Then,three optimum modified materials(15wt%Cu-nFe0?15 wt%Pd-Cu-nFe0(Pd:Cu=1:2)?Cu-nFe0/(Na Y)were selected for the nitrate cycle removal test.The results showed that the nitrate removal rate of all three materials decreased after four cycles,and Cu-nFe0/(Na Y)showed higher nitrate removal Rate(70.39%)after that,while the ammonia-nitrogen conversion rate of Cu-nFe0 and Pd-Cu-nFe0 nanoparticles decreases with increasing cycle,its' the ammonia-nitrogen conversion rate gradually increases to more than 40%in the cycle,giving us a belief that the material we made have the ability to be recycle and reuse.The Pd-Cu/active carbon(AC)catalyst was synthesized in the laboratory,and the two reducing agents nFe0 and H2 were combined with the catalyst to treat the nitrate,and the difference of the different nitrate removal effects of the reducing agent was compared.The results showed that the nitrate removal rate of the nFe0 experimental group was only 32.81%at the end of the reaction,which was lower than H2 experimental group,besides,the ammonia nitrogen conversion rate of the nFe0 experimental group(60.22%)was higher than the H2 experimental group(26.8%).Increasing the amount of catalyst to 4 g·L-1,the reactivity of nFe0 increased,nitrate removal rate increased to 76.51%,and the ammonia nitrogen conversion rate decreased to 35.25%.Therefore,under the synergistic effect of suitable catalysts,as an effective reducing agent,nFe0 is expected to replace H2.