Remediation Of Nitrate Nitrogen And Chromium Pollution In Groundwater By Embedding Nanoscale Zero Valent Iron

With the development of economy and society in recent years,the demand for groundwater has increased rapidly,and the discharge of industrial and agricultural wastewater and domestic sewage has also increased,resulting in the serious pollution of groundwater.The restoration of groundwater has become the most important environmental issue at present.Nitrate nitrogen?NO₃^--N?and chromium Cr???are long-term pollutants in groundwater and have great toxicity to human body.Chemical remediation is a fast and effective method.Nanoscale zero valent iron technology has become one of the most concerned research methods because of its high reaction activity and good removal efficiency.However nanoscale zero valent iron is unstable and easy to reunite,so it is limited in practical application.In order to solve this problem,nanoscale zero valent iron?nZVI?and diatom mud embedded nanoscale zero valent iron?DnZVI?were prepared by liquid phase reduction method and characterized by scanning electron microscope?SEM?and X ray diffraction?XRD?.The results showed that the nanoscale zero valent iron particles mostly existed in the form of chain,while the nanoscale zero valent iron particles embedded in diatom mud had good dispersion,which could solve the problem of the agglomeration of nanoscale zero valent iron.The effect of NO₃^--N removal by two kinds of materials was compared in the experiment.And the effects of different embedding ratio,DnZVI dosage,initial concentration of NO₃^--N and pH on the removal of NO₃^--N were investigated.The results show that under the same conditions,the removal efficiency of DnZVI is 22.25%higher than that of nZVI,and the optimum embedding ratio of diatom mud to nanoscale zero valent iron is 5:1;pH,which is an important factor affecting the removal of NO₃^--N by DnZVI,and the lower pH is beneficial to the reduction of NO₃^--N.When the pH is 3,the initial concentration of NO₃^--N is 40mg·L^-1,DnZVI dosage is 5g·L^-1,the removal rate of NO₃^--N was 99%.The main product of NO₃^--N removal was NH₄⁺,which accounted for 81%of NO₃^--N removal.The effect of DnZVI in different DnZVI dosage,Cr???solution initial concentration,pH,temperature on the removal of Cr???were investigated.The reusability of the material was also studied.The results show that when the temperature is 25?,the pH is 3,the dosage is 2g·L^-1,and the initial concentration is 10mg·L^-1,the removal efficiency of Cr???by DnZVI was the best,and the removal rate was 95.5%.After three times reuse of DnZVI and nZVI,the removal rate of Cr???by DnZVI was about 4 times that of nZVI.DnZVI reuse is better.The kinetic analysis of the reaction was carried out according to the experimental results.The results showed that the removal of NO₃^--N and Cr???from groundwater by DnZVI was in accordance with the first-order kinetic law under the influence of different pH,dosage,initial concentration and temperature.The activation energy of the reaction is 57.25 KJ·mol^-1 and 29.46 KJ·mol^-1,respectively.