The Effect of Humic Substances on Iron Elution in the Method of Restoration of Seaweed Beds Using Steelmaking Slag

Abstract

The transformation of formally productive coastal areas into barren ground is a serious problem in Japan and worldwide. Although several factors have been proposed for this phenomenon, this study especially focused on the effect of lack of dissolved iron in limiting the growth of seaweed beds. A method has been developed where a mixture of steelmaking slag and compost including humic substances, is supplied to seawater in order to stimulate seaweed bed restoration. This method increases dissolved iron concentration, since complexes called iron-humates are formed from the iron in steelmaking slag and the humic substances in compost. In this study, an evaluation was made whether humic substances increases dissolved iron concentration. A laboratory based iron elution test using seawater was attempted. Three kinds of samples were evaluated for iron elution namely, steelmaking slag in isolation, compost in isolation, and a mixture of steelmaking slag and compost. The change in dissolved iron concentration using each method was monitored over time. We found that the iron elution rate was more rapid within the mixture of steelmaking slag and compost than that in the steelmaking slag. Results of the study indicated that the structural characteristics of the humic substances were related to the increased iron elution from steelmaking slag. The method of using a mixture of steelmaking slag and compost was more effective not only for increasing dissolved iron concentration within seawater, but also for extending the life time of Fe elution.