Effect of the Mineralogical Phases in Steelmaking Slag Fertilizer on the Dissolution Behavior of Nutritious Elements and Rice Growth

Steelmaking slag contains various mineralogical phases, including water soluble phases such as free CaO and the solid solution consisting of 2CaO·SiO₂ and 3CaO·P₂O₅. However, the contribution of each of these phases to the rice growth through the supplement of nutritious element in the rice soil is not clear. In this research, we modified a commercial fertilizer made of steelmaking slag to produce one without the free CaO phase and another without either the free CaO or the solid solution of 2CaO·SiO₂ and 3CaO·P₂O₅. Experiments were conducted using these modified fertilizers, aiming to understand the dissolution behavior of the nutritious elements in aqueous solution with and without rice soil, and their effect on rice growth. As seen in the dissolution test in aqueous solution, an initial increase in Ca was suppressed by removing free CaO, and the dissolution of both Ca and Si decreased to half upon the removal of the solid solution compared with the original fertilizer. A column test that simulates the rice soil field showed that an initial increase in pH was suppressed, and the dissolution of Si and Fe increased by removing free CaO. Rice growth test showed that the Si content in both the soil solution and the rice uptake increased by removing free CaO but decreased when the solid solution was removed.