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| In this work the activation of peroxydisulfate (PS) with iron sulfide for pollutant degradation from aqueous solution was investigated and the application of the method for the in-situ purification of groundwater contaminated with perfluorinated alkanoic acids in particular perfluorooctanoic acid (PFOA) was prepared. It has already been shown in previous studies that iron sulfide is suitable for PS activation for the generation of sulfate radicals and first indications of a long-term stability of the activation process were found. In this dissertation the catalytic effect of iron sulfide during activation has now been demonstrated for the first time and a new surface-assisted reaction mechanism has been formulated. Based on the knowledge gained it could be shown in laboratory experiments that even PFOA can be oxidized by FeS-mediated activation of PS. Due to the processes of PS activation and adsorptive accumulation of PFOA which both take place on the FeS surface the mineralisation of this compound which is otherwise difficult to degrade was successful despite the presence of interfering ions such as chloride or nitrate. The processes that take place in the vicinity of the FeS surface could thus be decoupled from the reaction conditions of the water phase which would not have allowed oxidation of the PFOA. By using FeS as a PS activator oxidative contaminant destruction directly at the mineral surface was also successful in real groundwater and in the presence of site sediment. In this work the effect of the surface reaction on the product pattern was discussed and the difference to the homogeneous reaction was analysed mechanistically. By investigating the influence of the FeS surface on the sulfate radicals formed the present work was able to show that the oxidation of halogenated pollutants with surface-mediated radicals produced a different selectivity pattern compared to freely dissolved sulfate radicals. This supports the hypothesis that the reaction of sulfate radical and pollutant takes place under the influence of the surface of the iron sulfide. The knowledge acquired in the dissertation allows a better understanding of the activation process of PS by iron sulfide. The strategy of shifting the reaction of sulfate radicals and PFOA (as a representative of perfluoroalkanoic acids) to the activator surface provides a substantial contribution to being able to effectively destroy this extremely persistent class of substances in real waters as well which makes a future application in groundwater remediation promising. |
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