Removal Of Nitrate From Solution By Chelating Resin-supported Pd/Cu Catalyst And Zero Valent Iron

Excessive nitrate in water will threaten the safety of environment and organisms,so it is necessary to take appropriate methods to remove nitrate.Chemical reduction method has the advantages of convenient operation and no harmful by-products.In order to improve the nitrate reduction rate and N₂ selectivity,bimetallic catalysis was often used for nitrate removal.In this project,Pd/Cu-TP207 supported bimetallic catalyst was prepared by loading Pd/Cu on TP207 chelating resin.Zero valent iron with different sizes was used as reducing agent for nitrate reduction.The reaction of zero valent iron（ZVI）and nano zero valent iron（NZVI）-Pd/Cu supported catalyst system with nitrate under various influencing factors（metal ratio,dosage,initial pH,temperature,initial nitrate concentration,coexisting anions,supported matrix,reductant type,etc.）was studied.The removal of nitrate and total nitrogen and the generation of other nitrogen-containing products under different conditions were summarized.The mechanism and kinetics of the reaction were also discussed.The results showed that the supported Pd/Cu catalyst broadened the suitable pH range of the reaction and improved the N₂ selectivity compared with using iron powder alone.Among them,NZVI has a higher nitrate removal efficiency as reductant,but ZVI has a higher N₂ selectivity.Through a series of experiments and data analysis,the following conclusions were obtained:（1）ZVI system had the best nitrate removal efficiency under neutral conditions.When initial nitrate concentration was 30mg/L and ZVI dosage was 7.5g/L,nitrate removal was 63.16%and TN removal is 57.76%in 300min.N₂ in final product accounts for more than 90%.In contrast,a smaller amount of NZVI（1g/L）achieved a higher nitrate removal rate（87.07%）,but more than 50%of ammonia nitrogen was generated.（2）The mechanism study showed that the high selectivity of ZVI and Pd/Cu supported catalyst system to nitrogen under neutral conditions was mainly due to the lower Fe²⁺concentration,slower nitrate reduction rate and higher N/H ratio caused by the low corrosion rate of ZVI in neutral conditions,which reduced the formation of ammonia nitrogen.（3）The effects of catalyst or reductant dosage and initial nitrate concentration on the two systems were similar.With the increase of catalyst dosage and the decrease of initial nitrate concentration,the nitrate removal rate increased.Several coexisting anions used in the experiment all inhibited nitrate removal.The effects of pH and temperature on the two systems were different,mainly due to the difference between ZVI and NZVI.（4）The kinetic study shows that the reaction rate constant of using a small amount of NZVI as reducing agent is 2-30 times higher than that of using 7.5 times the dosage of ZVI as reducing agent under the same conditions.Through this study,we hope to find a nitrate reduction method with high nitrogen selectivity and nitrate removal rate,and provide a reference for related research.