Mechanism of Suppression of Sulfide Ion in Seawater Using Steelmaking Slag

In Japan, 15 million tons of steelmaking slag is produced annually as a by-product of the steelmaking process. It is known that steelmaking slag has specific properties to decrease hydrogen sulfide in seawater. To date, however, the specific mechanism is still unknown. This is the first report that explains the process of the slag reducing the hydrogen sulfide level. We added slag to the artificial seawater containing sulfide ion and obtained fine particles. We analyzed the reaction products with X-ray absorption fine structure (XAFS) and scanning electron microscopy-energy dispersive X-ray detector (SEM-EDX) and confirmed corresponding peaks of FeS, FeS2, sulfur and sulfate. We also measured the oxidation-reduction potential (ORP) and found that a shift to oxidizing atmosphere was promoted by adding slag, which oxidized sulfide ion to sulfuric acid ion. These data suggested that hydrogen sulfide level in seawater is reduced not only by the reaction of sulfide with iron contained in steelmaking slag but also by oxidation of sulfide in seawater with steelmaking slag. These results imply that effective utilization of steelmaking slag in coastal areas has a capability to improve the surrounding marine environment.