Influence of TiO 2 and Al 2 O 3 on the structure and sulphide capacity of the CaO–SiO 2 –MgO– x Al 2 O 3 – y TiO 2 slag system

Abstract

This work employed the slag–iron equilibrium method to study the effect of TiO₂ and Al₂O₃ content on the sulphur capacity of the CaO–SiO₂–MgO–xAl₂O₃–yTiO₂ slag system at 1500 °C. Using X-ray photoelectron spectroscopy (XPS) and molecular dynamics simulations, different types of oxygen in the slag and changes in the aluminate structure were analysed. The results indicated that as the TiO₂ content in the slag increased from 0 to 10 wt-%, the sulphur capacity decreased. It is known that an increase in TiO₂ content can reduce the polymerisation of the slag and improve ion transport efficiency within the slag, which is beneficial for enhancing the desulphurisation capability. However, the increase in TiO₂ content also resulted in a decrease in CaO content in the slag. At the same time, the complex aluminate structures depolymerised, consuming Ca²⁺ in the slag due to charge compensation requirements. This reduction in Ca²⁺ content available for desulphurisation in the slag further decreased its sulphur capacity. Additionally, when the Al₂O₃ content increased from 14 wt-% to 22 wt-%, the sulphur capacity of the slag also decreased. This is primarily because Al₂O₃ exhibits pronounced acidic behaviour in this slag system, acting as a network former that promotes the polymerisation of free oxygen into bridging oxygen and leads to the aggregation of simple aluminate structures, which complicates the slag structure. This increased complexity results in a reduced diffusion rate of ions within the slag, and the formation of the [AlO₄]⁴⁻ structure requires substantial Ca²⁺ for charge compensation, thereby further inhibiting the desulphurisation capability of the slag.