Comparison of desulfurization mechanism in liquid CaO-SiO2 and MnO-SiO2: An ab initio molecular dynamics simulation

In present study, systematic investigations of the CaO-SiO2 and MnO-SiO2 slag were performed of the evolution of the structure, and the sulfur dissolution mechanism at a temperature of 2000 K using ab initio molecular dynamics simulations. The results show that the structure and charge of CaO-SiO2 and MnO-SiO2 are very different. Firstly, Si-O has a strong polar bond while Ca-O and Mn-O show ionicity, and Mn-O has weaker ionicity than Ca-O. A small amount of Mn-Mn clusters are found in liquid MnO-SiO2. Secondly, charge distribution depicts that there is less charge around Ca, while there are relatively more charges around Mn. Bader charge analysis indicates that Mn and O have a broad valence distribution in MnO-SiO2 compared with CaO-SiO2. Thirdly, Sulfur prefers to form stable bonds with Mn atoms (Mn-S-Mn), whereas Si-S bonds are unstable and cannot be found in S-doped MnO-SiO2 silicate. However, in the CaO-SiO2 system, the S atom does not undergo rapid bond transitions. The study of the desulfurization mechanism shows that the uneven distribution of charge in MnO-SiO2 system will affect the transformation of oxygen types, resulting in the decrease of bridged oxygen and the increase of non-bridged oxygen. However, there is no charge effect in CaO-SiO2 system, and the non-bridged oxygen will be consumed in the desulfurization process, resulting in the decrease of non-bridged oxygen and the increase of bridged oxygen. This mechanism well explains the experimental results from a more microscopic perspective, which is of great significance to the research on the removal mechanism of S in the metallurgical industry.