Research On The Modified Of Nano Zero-valent Iron And Its Properties And Mechanism For Pollutants In Water

With the development of industry,agriculture and urbanization in China,nitrate?NO₃^-?and heavy metals pollution in water were seriously threaten human health.In recent years,nano-zero-valent iron?nZVI?has received extensive attention due to its strong ability to reduce NO₃^-and Cr???.However,the pure nano-zero-valent iron reduces nitrate and the reduction products are mostly ammonia nitrogen,and the selectivity to nitrogen is low;while the reaction of pure nano-zero-valent iron with Cr???only the highly toxic Cr???is reduced to low toxicity Cr?III?,but it did not solve the problem fundamentally,thus limited the use of nZVI.Therefore,finding a suitable supporting material,increasing the reduction selectivity of NO₃^-and reducing the Cr???characteristics is an urgent problem to be resolved.In this study,we develop a new composite material of Fe-Cu/D407composite via using nanoscale zero-valent iron with copper deposited on chelating resin to remove nitrate from the water.The experimental results show that a remarkable nitrate removal and the selectivity of N₂ are 99.9%and 89.7%,respectively,under the anaerobic conditions of Cu/Fe molar ratio of 1:2,pH=3.0,NO₃^--N 50 mg/L.Even without of inert gas and adjusting the initial pH of the solution,the removal rate of nitrate by Fe-Cu/D407 reached to 85%and the selectivity of nitrogen reached to 55%.Meanwhile,the Fe-Cu/D407 maintained preferable removal efficiency of nitrate?100%-92%?over a wide pH range of 3-11.In addition,the removal rate of the drinking water,lake water and wastewater from the Fe-Cu/D407 is still very high and the reactivity of Fe-Cu/D407 was relatively unaffected by the presence of dissolved ions in the waters tested.Moreover,the synergetic effect of Fe,Cu and D407 in the composite Fe-Cu/D407were well investigated for the first time according to the analyses of TPR,XPS and EIS.The catalytic mechanism and denitrification routes were also proposed.In addition,in the current paper,we studied to a sulfidated nanoscale zerovalent iron?S-nZVI?for enhanced removal of Cr???in solution and sodium thiosulfate was used as the sulfur source.The experimental results show that whenthe initial concentration of Cr???is 50 mg/L and S-nZVI?S/Fe=0.1?,the Cr???solution can be completely removed at pH=3 and without oxygen or air condition.However,the removal efficiency with Cr???was only 20%by nZVI.It is worth noting that only FeCr₂S₄ was generated under anoxic and acidic conditions in the new process.Accordingly,we proposed a new reaction process of Cr???reduction by S-nZVI under anoxic condition.The improving effects of sulfidation on the performance of nZVI were mainly due to the following mechanisms:sulfidation increased the specific surface area of nZVI,the FeS_x layer facilitated the enrichment of Cr???anions on S-nZVI surface because of its anions selective property and favored the electron transfer from Fe⁰ core to Cr???at the surface because of its role as efficient electron conductor.Meanwhile,the surface of FeS_x participated in the reaction.