Effects of three iron material treatments on hydrogen sulfide release from anoxic sediments

In eutrophic coastal regions, hydrogen sulfide (H₂S) is a harmful material released from sediments under anoxic conditions. To suppress its release, we conducted laboratory experiments and assessed the impacts of treatment with three iron materials (Fe, Fe₂O₃, and FeOOH), focusing on the area-specific H₂S release rate. These materials qualitatively exhibited a substantial suppression of H₂S release; however, smaller treatment levels (<150 mmol m^-2) were ineffective. FeOOH exhibited the best performance, followed by Fe₂O₃, and Fe. These differences were likely caused by variations in the oxidation or reduction potential of the materials and their reaction rates with H₂S. A simplified model suggested that the required minimum Fe²⁺ concentration was determined using the H₂S diffusivity, reaction rate constant, and treatment penetration depth. As the former two are physical constants, the latter must control the H₂S release rate. Iron materials were experimentally confirmed to persist for over three weeks, and the effective treatment level was theoretically estimated as being capable of suppressing H₂S release for more than a year. Our results will contribute to coastal environmental management and particularly benefit port authorities who manage enclosed and eutrophicated harbors and navigation channels where slag application should be avoided.