Novel recycling process of Mn by sulfurization of molten slag from a by-product of steelmaking process

We propose a novel process to recycle Mn from steelmaking slag. The first step is to sulfurize the slag, producing a liquid sulfide phase (matte) without P. High-purity Fe-Mn alloys can then be made by desulfurizing the matte. However, to our knowledge, there have been no reports to date concerning the sulfurization of P and Mn contained in molten slag. Therefore, knowledge of the distribution of Fe, Mn and P between the matte and the molten slag is required to determine the feasibility of this process. In this study, the equilibrium distributions of Mn, Fe, Ca and P between a FeS-MnS matte and FeO-MnO-SiO ₂-MgO-P ₂O ₅ slag with/without CaO are investigated under controlled partial pressures of oxygen and sulfur. It was found, as P is not present in the matte, that a separation of P from Mn was accomplished. The increament of (CaOCMgO)/SiO ₂ in slag can improve the concentrations of Mn and Fe in the matte. The content of Ca in the matte was less than 2 mass%, even when the concentration ratio of CaO/SiO ₂ in the slag was unity.