Regeneration of manganese oxide as adsorption sites for hydrogen sulfide on granulated coal ash

•The regeneration of adsorption site for H2S on granulated coal ash (GCA) was studied.•Manganese oxide is an adsorption site for H2S on the GCA.•Manganese oxide was reduced and coupled with H2S oxidation under anoxic condition.•Reduced manganese oxide was oxidized or regenerated under oxic condition.•The regenerated manganese oxide could adsorb and oxidize H2S.

It is important to remove hydrogen sulfide to maintain healthy ecosystems as well as viable aquaculture activities in enclosed water bodies. Granulated coal ash with high adsorption capacity for hydrogen sulfide is a by-product generated from coal combustion processes in coal-fired power plants. The purposes of this study were to (1) verify the regeneration of the adsorption sites for hydrogen sulfide on the granulated coal ash by redox reaction which changes between oxic and anoxic conditions and (2) prove the regeneration mechanisms of the adsorption site which leads to high adsorption capacity for hydrogen sulfide. XAFS analyses of the granulated coal ash revealed that the adsorption site for hydrogen sulfide on the granulated coal ash was regenerated at least 10 times through oxidation of manganese oxide under oxic conditions. A positive correlation (r = 0.995) between the peak top energy of manganese XAFS in the GCA collected from field trial sites and the Eh of the sediments applied with the GCA was observed. These results proved that hydrogen sulfide was adsorbed and oxidized by the granulated coal ash during the stratified season. During the vertical mixing seasons, oxygen regenerates the adsorption site for hydrogen sulfide. It is concluded that this regeneration of adsorption site gives the granulated coal ash high adsorption capacity for hydrogen sulfide.