Article ID: ISIJINT-2025-248
An efficient new process for hot metal pretreatment using the converter was developed, in which the whole amount of dephosphorization slag in the preceding charge is left in the converter and is hot-recycled to the following charge following intermediate deslagging after the desiliconization period. In this process, it is necessary to avoid rephosphorization from the phosphorus-containing slag. Therefore, in this study, a series of plant trials was carried out to investigate the change in the phosphorus content of the hot metal. During the desiliconization period, rephosphorization or dephosphorization was observed depending on the slag basicity. Rephosphorization occurred under conditions such that the slag composition corresponded to the coexistence of CaO･SiO2 (CS) and liquid slag (L), provided that the slag was substantially considered as a [CaO-SiO2-FeO] ternary system. On the other hand, dephosphorization proceeded under conditions such that the slag was saturated with 3CaO･2SiO2 (C3S2) and/or 2CaO･SiO2 (C2S) based on the ternary diagram. According to the available data, the phosphorus distribution ratio in a condition of 3-phase coexistence of CS+C3S2+L and C3S2+C2S+L is on the order of 103 to 104, but decreases to below 102 in the CS+L region. The range of slag basicities for such a high phosphorus distribution ratio is strongly affected by the FeO content in the slag. Considering kinetic advantages as well as equilibrium conditions, the optimum FeO content for preventing rephosphorization from the recycled slag while also proceeding with phosphorus removal sufficiently in a commercial operation is discussed, and is proposed to be around 15 mass% FeO.
