To produce fertilizer made of steelmaking slag, the combination of mineralogical phases is necessary to be appropriate not only for refining at high temperature, but also for supplementing nutrient elements in paddy fields. In this research, first, the variations in the chemical composition and mineralogical structure of various brands of fertilizer made of steelmaking slag were investigated. The basicity (CaO/SiO2), free-CaO content, total Fe content, and Fe2+/Fe3+ ratio of fertilizer were found to vary widely depending on the brand. In addition, regarding the mineralogical phases, solid solution consisting of 2CaO·SiO2 and 3CaO·P2O5, MgO–FeO, CaO–Fe2O3, free CaO, metallic Fe, and the other phase which included liquid phases at refining temperature were observed. The mass fraction of each phase also varied depending on the brand. Second, the dissolution behavior of each mineralogical phase in the fertilizers into water that simulated the early stage of flooding condition was studied. Regarding the dissolution of Ca, free CaO dissolved in a short time, and the solid solution of 2CaO·SiO2 and 3CaO·P2O5 dissolved slowly. Fe barely dissolved from any mineralogical phase except the other phase which consisted of CaO–SiO2–FeO. A clear relationship was observed between the dissolution of Fe and the mass fraction of other phase as well as the ratio of Fe2+ to Fe3+ in Fe oxides in fertilizer made of steelmaking slag.
- Steelmaking slag