Elements distribution and interfacial structure of CaO-SiO2-10mass% MnO under CO-CO2-SO2-Ar gas

Highlights: • XPS method proved that Mn and S exist as positive divalent(Mn²⁺) and negative divalent(S^2-), respectively at the gas-slag interface. • Comparing XPS and Raman, the structure of the CaO-SiO₂-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. -- Abstract: In this work, the interfacial element distribution and structure of CaO-SiO₂-10%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 (S^2-), 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-SiO₂ system, while the interfacial structure information tends to the MnO-SiO₂ 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.