Utilization of steelmaking slag at marine environment for coastal revegetation

摘要

Due to lack of nutrient elements supply such as iron for the multiplication of photoplankton and seaweeds, recently barren grounds without seaweed in coastal areas present serious environmental problems not only in Japan but also around the world. Because of various oxide constituents such as FeO, SiO2, CaO and P2O5, low cost and abundant quantity, steelmaking slag is regarded as one of the best suitable candidate materials for providing nutrient elements for restoring seaweed beds. Ferrous ion is the obligatory nutrient element for growth of seaweed. However it is easy to be oxidized to form ferric hydroxide colloid in the presence of dissolved oxygen in seawater. It is well known that the dredged soil contains various kinds of organic acid such as fulvic acid and humic acid, and these organic acids can chelate iron ion to stabilize it and improve its solubility. For effective utilization of steelmaking slag at marine environment for coastal revegetation, in the present study, the shaking experiment of synthesized steelmaking slag and dredged soil mixture was conducted to investigate the dissolution of Ca, Si, Al, Fe and P. The dissolution of Ca from slag-soil mixture results in increasing the pH of the shaking solution. Mg provides a buffering action when pH reaches a certain extent. Simultaneously soil also provides a buffering action on the whole pH increasing process. The dissolved iron is estimated to equilibrate with Fe2O3 phase, since the oxidation - reduction potential (ORP) value of solution is in the condition of the Fe2O3 stable area in the potential-pH diagram.