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• XPS method proved that Mn and S exist as positive divalent(Mn2+) and negative divalent(S2-), respectively at the gas-slag interface. • Comparing XPS and Raman, the structure of the CaO-SiO 2 -MnO slag has a gradient change trend from the interface to the body due to uneven distributions of elements. • Mn and S have a strong correlation, which is due to the existence of Mn cluster and the uneven distribution of charges. In this work, the interfacial element distribution and structure of CaO-SiO 2 -10%mass MnO slag was explored using the gas-slag equilibrium experimental method and XPS detection method at the temperature of 1873 K. Based on the full spectrum, the relative content of sulfur gradually decreases, the manganese has the same trend, while the calcium content keeps increasing. According to the analysis of the Mn2p and S2p spectra, it indicated that Mn and S exist as positive divalent (Mn2+) and negative divalent (S2-), respectively. The O1s fitting result indicates that the proportion of non-bridged oxygen (O-) increased, while that of bridged oxygen (O0) decreased with the etching time increased. The structural units obtained by Raman spectroscopy are closer to the evaluation data of the CaO-SiO 2 system, while the interfacial structure information tends to the MnO-SiO 2 system. Although CaS is thermodynamically more stable than MnS, the reason for the sulfur accumulation in the gas-slag interface is due to the d electron supplement from Mn. Thus, the concept of interface sulfide capacity is proposed. As the etching depth increases, the interface sulfide capacity decreases continuously. Comparing XPS and Raman, the structure has a gradient change trend at the gas-slag interface, which confirms the presence of the boundary layer at the gas-slag interface. [ABSTRACT FROM AUTHOR]

• AIMD method is used to calculate structure and charge information of the liquid slag. • The stable state and environmental information of sulfur in liquid silicate is obtained. • The desulfurization mechanism of the two systems was elucidated based on charge analysis. [Display omitted] In present study, systematic investigations of the CaO-SiO 2 and MnO-SiO 2 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-SiO 2 and MnO-SiO 2 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-SiO 2. 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-SiO 2 compared with CaO-SiO 2. 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-SiO 2 silicate. However, in the CaO-SiO 2 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-SiO 2 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-SiO 2 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. [ABSTRACT FROM AUTHOR]