The Reduction Of Cr(VI) Over The Interface Between Iron/Manganese Oxides And Shewanella

With the wide application of chromium in industrial production,chromium pollution has gradually become a research hotspot.Through biological reduction,Cr?VI?with greater toxicity can be transformed into less harmful Cr?III?.Microorganisms usually adhere to solid minerals with each other,which will affect the reduction process of microorganisms,especially when elements like iron and manganese are present in minerals.Therefore,the study of the Cr?VI?reduction process at the microbial-mineral interaction interface is of great significance.In this study,two typical iron and manganese oxides?goethite,birnessite?and the typical dissimilatory metal-reducing strain Shewanella Oneidensis MR-1 were chosen and the reduction of Cr?VI?over the interface between them was studied.From the morphology and the analysis of surface charge,sites and functional groups of Shewanella-iron/manganese oxides interaction interface,we get the following results:1.Goethite increased the negative charge on the surface of Shewanella,and the birnessite reduced the negative charge on the surface;sites of Shewanella coverd up after composed with the two minerals.With the increase of goethite,the sites decreased.But the concentration of birnessite has no effect on the concentration of surface sites.The low concentration of birnessite and goethite has little effect on the metabolism of Shewanella,and the high concentration of birnessite inhibited the metabolism of Shewanella.2.Under different pH conditions,the reduction rate of Shewanella and its composites with goethite and birnessite increased with the increase of pH.The order of reduction rate of different composites was:Shewanella-Goethite>Shewanella-birnessite>Shewanella.Goethite,birnessite and electron shuttles increased the adsorption of Cr?VI?onto the surface of solid phase.The total chromium concentration in the solution does not change significantly with time,which illustrated that the Cr?VI?reduced to soluble Cr?III?mainly.3.Under different initial Cr?VI?concentration,the reduction rate of Shewanella,Shewanella-goethite and Shewanella-birnessite decreased with the increase of initial concentration.The order of reduction rate of different composites was:Shewanella>Shewanella-goethite?Shewanella-birnessite.Electron shuttles promote the reduction of Cr?VI?at low concentrations,and the products of reduction were mainly in the form of soluble Cr?III?.4.The existence forms of Cr?VI?reduction products on the surface of solid phase include:Cr₂O₃,Cr?OH?₃ and a little CrO₄^2-,with Cr₂O₃ as the main form.There is FeCr₂O₄ existented on the surface of Shewanella-goethite.Shewanella can reduce birnessite and goethite,and the reduction of minerals produced Fe?II?and Mn?III?participated in the Cr?VI?reduction.5.By ATR-FTIR/2D-CoS,the order of interaction between Shewanella,birnessite and goethite and Cr?VI?was got:birnessite?Shewanella?goethite.The order of functional groups of Shewanella-birnessite interacted with Cr?VI?was:O-Mn-O?amide II?amide I?MR-1 PO₂^-?MnO₆ octahedral structure?monodentate complex PO₂^-?CH₂/CH₃.The order of functional groups of Shewanella-goethite was:monodentate complex PO₂^-?CH₂/CH₃?amide I?amide II?Fe-O?Fe?OH?Fe-O.