Thermal physical properties and dephosphorisation kinetics of rare earth oxides containing slags

Abstract

The melting properties and viscosity of CaO-SiO 2 -MnO-La 2 O 3 -CeO 2 slags, with mass ratios of 0.97 and 1.05 between CaO and SiO 2 , were measured using the hot stage microscopy method and rotating cylinder method, respectively. In addition, the dephosphorisation kinetics of rare earth (RE) oxides containing slags was studied. For increasing mass contents of the RE oxides, La 2 O 3 and CeO 2 (0, 3, 6, 9, and 12 wt.%), in the slag, the melting temperature initially decreases and then increases. Minimum values appeared for mass contents of 6 wt.%. RE oxide concentrations below 9 wt.% are beneficial to the decrease in viscosity, which increases significantly with the mass fraction of RE oxides in molten slags with a basicity of 1.05. In slags with a basicity of 0.97, the RE oxides favour the decrease in viscosity, which does not change noticeably as their mass fraction is increased above 6 wt.%. Finally, it was found that the rate-limiting step of the dephosphorisation process is the diffusion of phosphorus.

Dephosphorization of hot metal using rare earth oxide-containing slags

“…However, dephosphorization process is a liquid phase reaction, controlled by material diffusion in the liquid phase and interface chemical reaction. A lower temperature leads to an uneven melting of the slag, and the transfer of material is rate-limiting, which leads to a poor kinetics of dephosphorization [16]. Therefore, when the temperature is below 1,550°C, the dephosphorization efficiency is mainly influenced by the kinetics, and an increase in temperature up to 1,550°C causes an increase in dephosphorization efficiency.…”

“…Based on these conditions, Xi et al [14] distribution between CaO-SiO 2 -MnO-Ce 2 O 3 -La 2 O 3 slags and ferromanganese alloy, and the results showed that an increase in the RE oxide content in molten slags improves the phosphorus distribution ratio. However, RE oxides have a limited solubility in molten slags [15], while excessive RE oxides in the slags cause an increase in the molten temperature and viscosity, thus deteriorating the dephosphorization kinetics [16].…”