Effects Of Surfactants On The Reduction Of Nitrobenzene By Fe(Ⅱ) Bearing Minerals

In the anaerobic environment such as groundwater, the structural iron of iron minerals and clays can be reduced into Fe(II) bearing minerals by iron reducing bacterium and natural organic matters. The Fe(II) bearing minerals bearing higher reductive capacity than that of aqueous Fe(II), can reduce and degrade some oxidizing organic contaminants such as nitrobenzene, chlorinated compounds, and this is the main transformation routine for these contaminants in anaerobic environment.The recent studies have shown that the coexisting agents in anaerobic environment including humic substances, metal ions with changing valence can influence the reaction between Fe(II) bearing minerals and contaminants. Owing to that this reduction of contaminants by Fe(II) bearing minerals is a surface reaction, the coexisting every surfactant affects the enrichment of contaminants on the surface of iron minerals, and some functional groups of surfactants also change the microenvironment on the reaction interface between Fe(II) bearing minerals and contaminants. But till now, the effects of surfactants on the reduction of organic contaminants by Fe(II) bearing minerals has never been studied. Therefore, the study on the influence and mechanism of surfactants on the reduction of organic contaminants by Fe(II) bearing minerals is helping to understand the migration, transformation and fate of organic contaminants in anaerobic environment deeply.In this work, nitrobenzene was chosen as a model contaminant, nonionic octylphenol polyethoxylete(TX-100), anionic sodium dodecyl benzenesulfonate(SDBS), cationic hexadecyl trimethylmmonium bromide(CTMAB), biosurfactant(saponin), nonionic-anionic surfactants(TX-100/SDBS)and nonionic-cationic surfactants( TX-100/CTMAB) was selected to investigate their effects on the reduction of nitrobenzene by Fe(II) bearing two minerals(goethite, nontronite). The adsorption of nitrobenzene on iron minerals, sorption amount of Fe(II) on iron minerals, the potential of Fe(III)/Fe(II) and the concentration of reactant and product before and after addition of surfactant were mainly investigated, and the mechanism of surfactant on the reduction of organic contaminants by Fe(II) bearing minerals had been clarified preliminarily. The research results are listed as follows:(1) In the reduction system of nitrobenzene by Fe(II) bearing nontronite, the selected surfactants enhanced nitrobenzene reduction by CTMAB or TX-100. However, saponin or SDBS decreased reduction efficiency at different extents. Two mixed surfactant(TX-100/SDBS and TX-100/CTMAB) with different ratios also showed the same positive effects of nitrobenzene degradation as each one.(2) In the reduction system of nitrobenzene by Fe(II) bearing goethite, the presence of TX-100 or CTMAB was confirmed to promote the reduction of nitrobenzene. But the reduction efficiency of Fe(II) bearing nontronite was enhanced more significantly than that of Fe(II) bearing goethite in the presence of surfactant However, saponin or SDBS decreased reduction efficiency at different extents.(3)The main effects of surfactants on the reduction of nitrobenzene by Fe(II) bearing minerals were concluded as follows: 1)The surfactants changed the adsorption of nitrobenzene adsorbed on the surface of minerals, influencing the electron transfer between the sorbed nitrobenzene and Fe(II) bearing minerals. 2) The surfactants also influenced the sorbed amount of Fe(II) on mineral and the potential of Fe( Ⅲ)/Fe( Ⅱ). The lower potential of Fe( Ⅲ)/Fe( Ⅱ) was, the remove rate of nitrobenzene would be higher. 3) The reduction of nitrobenzene was nearly equal to the production of aniline in the system of Fe(II) bearing minerals. The reductive performance of Fe(II) bearing minerals was enhanced with addition of surfactant, improving the reduction rate of nitrobenzene.