Iron sulfide and other surface Fe(II) compounds such as surface-associated Fe(II) and siderite are commonly found in natural systems such as groundwater, soil and sediment environments where the iron minerals react with hydrogen sulfide or are biologically reduced under anaerobic conditions. They can also be formed in the engineered systems where Fe(III) is used to remove hydrogen sulfide in sewers, wastewater treatment plants and in sour gases. Iron powders and granules are also used to control the gradual emission of hydrogen sulfide from sediments. When chemical oxidation is introduced into the subsurface and wastewater for pollutant remediation and disinfection and into the sediment phase for iron granule regeneration, the interactions of iron sulfide and surface Fe(II) compounds with the dosed chemical oxidants are important but unclear. This study discusses the interactions of Fe(II) compounds with persulfate, hydrogen peroxide and chlorine under conditions simulating the regeneration of granular ferric hydroxide (GFH) after it is covered with iron sulfide and Fe(II) compounds for hydrogen sulfide removal. Persulfate, hydrogen peroxide and chlorine of 10 mM effectively oxidized the iron sulfide and surface-associated Fe(II) compounds back into ferric hydroxides and elemental sulfur to recover the sulfide removal capacities (90, 87 and 80%, respectively) of the used GFH in the aqueous and sediment phases. The ferric hydroxides generated were mainly in the amorphous form with high surface areas and reactivity towards hydrogen sulfide. The Fe(II) oxidation reactions are speculated to involve homogeneous oxidation of released Fe<sup>2+</sup> ions and heterogeneous oxidation of the surface Fe(II) by the oxidants and also by radicals including sulfate radicals and hydroxyl radicals produced from the Fenton-like reactions. Detailed investigation is on-going to elucidate these mechanisms and their contributions to the regeneration of GFH under different environmental relevant conditions.

Reactions of iron sulfide and surface Fe(II) compounds with persulfate, hydrogen peroxide and chlorine

251st National Meeting (2016)

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