Effect Of Fe²⁺ On Nitrate Reduction Using Zero-valent Iron And Optimization Of Parameters Of In-situ Nitrate Remediation

Groundwater nitrate contamination is the most common type of groundwater pollution.Zero iron(Fe0)as a reducing agent,is widely used in groundwater nitrate in-situ and ex-situ remediation.However,it's difficult to save acidified Fe0 in practical applications,Fe0 usually has an oxide film.In this study,the removal efficiency of nitrate removal and the removal mechanism of Fe0 with oxide film,Fe2+and Fe3O4 were studied.The effects of different concentrations of Fe2+,iron sand ratio and different hydraulic retention time on NO3--N removal rate and its removal efficiency were studied by batch experiments,and the mechanism of synergistic effect was analyzed The main conclusions are as follows:(1)The effect of different concentration of Fe2+on the removal of NO3--N by Fe'reduction showed that the presence of Fe2+could promote the reduction effect of non-acidified Fe0 on NO3'-N,and the higher Fe2+concentration,The faster the removal rate and the higher the removal efficiency of NO3--N.When the concentration of Fe2+was increased from 20 mg·L-1 to 200 mg·L-1,the removal rate increased from 13.3%to 82.6%at 12 hours.However,the NO3--N reduction rate was slower in the initial stage of the reaction because of the oxide film on the surface of the acid without Fe0.Fe2+ could converts Fe2O3 on the surface of Fe0 into Fe3O4,which will accelerate the transfer of electrons from Fe0 to NO3--N,which is the main reaction mechanism of Fe2+ promoting Fe0 reduction of NO3--N.The results show that the higher Fe2+concentration,the higher Fe2+ per unit mass Fe0,the higher the presence of NO3--N also has a significant effect on the transformation of surface oxide film.(2)The effect of Fe3O4 on NO3--N reduction in Fe3O4 was studied.It was found that the addition of Fe3O4 and Fe0 in NO3--N solution had no effect on the reduction efficiency of NO3--N When Fe3O4,FeO and Fe2+were simultaneously,When Fe2+was added,Fe3O4 will accelerate the reduction of NO3--N to a certain extent and improve the removal rate of NO3--N.(3)The actual groundwater environment was simulated by column experiment.The effect of filling iron sand ratio and hydraulic retention time on NO3--N removal was investigated.The results showed that the higher the content of iron sand in the filling medium,the higher the NO3--N removal rate.The removal rates of NO3--N were 96.86%and 87.74%respectively,when the nitrate concentration was 103.79mg·L-1,the contents of iron were 100%,75%,50%and 25%respectively.68.64%,31.97%.The higher the NO3--N concentration,the lower the NO3--N removal efficiency,but the greater the absolute removal.The longer the hydraulic retention time,the higher the NO3--N removal rate.The removal rates of NO3--N in the No.1 column were 100%,84.6%and 65.1%,respectively,when the residence time of the solution in the reaction medium was14.54 h,7.27 h and 2.91 h,respectively.