Effects of basicity, MgO and MnO on mineralogical phases of CaO–FeO_x–SiO₂–P₂O₅ slag

Abstract

The selective separation phosphorous rich phase from steel slag could be an effective way to utilise the steel slag. The mineralogical phase after cooling of steel slag is essential to selective separation of steel slag. In the present work, the mineralogical phases of CaO-FeO x -SiO 2 -P 2 O 5 slag after controlled cooling were investigated by X-ray diffraction and scanning electronic microscopy and energy dispersed spectroscopy technique. It was found that the heat treatment at 1573 K would lead to the precipitation of Ca 2 SiO 4 -Ca 3 P 2 O 8 (C2S-C3P) solid solution for all samples. The heat treatment at 1273 K would lead to the precipitation of C2S-C3P, CaSiO 3 and Fe 2 O 3 . The increase of basicity would promote the crystallisation of CaO-FeO x -SiO 2 -P 2 O 5 slag. The Effects of additions of MgO and MnO on phase formations of CaO-FeO x -SiO 2 -P 2 O 5 slag were also studied. Fe 2 O 3 gradually transformed into MgFe 2 O 4 and MnFe 2 O 4 in slag after crystallisation with addition of MgO and MnO, respectively. The sizes of MgFe 2 O 4 and MnFe 2 O 4 crystals increased with increases of MgO and MnO content. The increase of MgO and MnO content would promote the precipitation of MgFe 2 O 4 phase and MnFe 2 O 4, respectively. The precipitation of crystals from slag during cooling was interpreted by the kinetic and thermodynamic factors. It was proposed that addition of MgO and MnO in slag would be beneficial to magnetic separation of steel slag.

Structural Characteristics and Hydration Kinetics of Oxidized Steel Slag in a CaO-FeO-SiO2-MgO System

“…According to Yadav [36] and Xue [37], MgO has a more positive role in restraining the formation of Fe 2 O 3 and promoting the formation of (Mg, Fe)Fe 2 O 4 in low basic slag. Shu also believed that the addition of MgO not only induce the precipitation of MgFe 2 O 4 spinel but also promote the crystallization of steel slag [38]. As the heating temperature reaches 1000°C, Mg 2 + replaces some of Fe + from the magnetite lattice by solid state diffusion, forming mixed spinels [36,39].…”

Effect of the Initial P Content on Dephosphorization of Hot Metal with Low Basicity Slag at 1623 K

“…[7] In addition, the mineralogical structures of the slag were also reported at low temperature and low basicity. [11][12][13][14][15] For example, Han et al indicated that the dephosphorization slag containing CaO•SiO 2 (CS), 2CaO•SiO 2 (C 2 S), and 2CaO•SiO 2 -3CaO•P 2 O 5 (C 2 S-C 3 P) is favorable for dephosphorization before the intermediate deslagging in the NDSP. [13] Zhou et al reported that the phosphorus is mainly enriched in the multiphase slag in the phase of C 2 S þ nC 3 P (n ¼ 1.1064-1.4303) at high phosphorus content and the phase of 6C 2 SþmC 3 P (m ¼ 0.6294-1.3400) at low phosphorus content in hot metal pretreatment.…”

Effect of the Basicity on Mineralogical Phases and Micro-Structure of Dephosphorization Slag in the New Double Slag Converter Steelmaking Process

“…There were some previous studies on the effect of basicity on the mineralogical phases of the dephosphorization slag [3,4,6,[8][9][10][11]. For example, Lin et al studied the effect of basicity on the mineralogical phases of CaO-SiO 2 -MgO-Al 2 O 3 -Fe t O-P 2 O 5 slag by cooling the evenly melted slag to 1623 K. It was found that the crystal sizes of metal oxides (RO) or spinel phases become smaller in higher basicity slag and the P content in the nC 2 S-C 3 P solid solution increased with the decrease of the basicity [9].…”