Effect of Humic Substances on Iron Elusion in the Method of Restoration of Seaweed Beds with Steelmaking Slag

Abstract

Barren grounds in coastal area are serious problems in Japan and throughout the world. Although several factors have been proposed to account for barren grounds, we have especially focused on lack of dissolved iron for restoring seaweed beds. It has been developed a method that the mixture of steelmaking slag and humus materials, such as composts, were supplied in seawater. A concentration of dissolved iron can be increased by using the method, since complexes, iron-humates, are produced from iron in steelmaking slag and humic substances in compost. In this study, we evaluated the effect of humic substances in this method for increasing dissolved iron concentration. A laboratorial iron elution test by using actual seawaters was attempted. Three kinds of samples for iron elution, only steelmaking slag, only humus materials, and a mixture of steelmaking slag and humus materials, were prepared. The change of iron concentration in each small tank had been monitored. We found that iron elution rate in the case of the mixture of steelmaking slag and compost was faster than that in the case of only steelmaking slag. Furthermore, it was expected that the characteristic of the structure of humic substances were related to increase iron elution from steelmaking slag. The mixture of steelmaking slag and humus materials was more effective not only for increasing iron concentration in seawater and but also for extending the life time of Fe elution.