Sulfide Capacity of CaO–SiO₂–MnO–Al₂O₃–MgO Slags at 1873 K

Abstract

The sulfide capacities of the CaO-SiO2-MnO-Al2O3-5 mass% MgO slags were measured at 1 873 K over a wide composition range using a gas-slag equilibration method. The effects of basicity and the activity coefficient of sulfide on the sulfide capacity of molten slag were also investigated based on the structural view of silicate melts. In the multicomponent silicate melts containing high MnO (up to about 50 mass%), the sulfide capacity mainly increased with increasing MnO content. The capacity and modified Vee ratio, i.e. (CaO+MnO+MgO)/ (SiO2+Al2O3), showed a good linear relationship. Assuming that the basicity and the stability of sulfide ions in the slag are proportional to the activity of basic oxides and the activity coefficient of sulfides, the composition dependency of the sulfide capacity is well described by changes in the aMO to γMS (M=Ca, Mn) ratio. The substitution of silica by alumina did not affect the sulfide capacity of the slags not only because of an increase in the activity of basic oxides but also because of a decrease in the stability of sulfides as Al2O3/SiO2 ratio increased. In the high silica melts of which silica content greater than about 30 mass%, the sulfide capacity increased with increasing MnO/CaO ratio, whereas it decreased by increasing the MnO/CaO ratio in the low silica melts (< about 30 mass%). This tendency of sulfide capacity resulted in the clock-wisely rotating iso-capacity contours in the CaO-SiO2-MnO-Al2O3-MgO system at 1 873 K. The dissolution mechanism of sulfur in the MnO-containing calcium silicate melts can be explained not only by the difference in the structural role of Ca 2+ and Mn 2+ ions but also by the changes in the content of O 2-ions according to the silica content.KEY WORDS: sulfide capacity; CaO-SiO2-MnO-Al2O3-MgO slag; basicity; sulfide stability; silicate structure; free oxygen.

Structure^|^ndash;Property Correlations of CaO^|^ndash;SiO2^|^ndash;MnO Slag Derived from Raman Spectroscopy

“…[22][23][24][25][26][27][28][29][30][31][32] In the study of nuclear magnetic resonance (NMR) spectra of silicates, [33][34][35][36][37][38] the stoichiometric notations for each unit were replaced by so-called Q n concept, wherein they are equivalent to Q 4 (NBO/Si = 0), Q 3 (NBO/Si = 1), Q 2 (NBO/ Si = 2), Q 1 (NBO/Si = 3), and Q 0 (NBO/Si = 4), respectively. Even though there have been several studies on the physicochemical properties of the CaO-SiO2-MnO slag due to its importance in smelting and refining processes for the production of manganese ferro-alloys as well as high manganese steel grades, [39][40][41][42][43][44][45] the systematic and fundamental approach on the structure of this slag system is scarcely found. Zebger et al 46) proposed from the ultraviolet reflectivity of the molten and glassy states of the CaO-SiO2-MnO system that the tetrahedral MnO4-complex is formed in liquid state.…”

“…Jung et al 47) measured the relative content of three types of oxygens such as bridging (O 0 ), nonbridging (O -), and free oxygen (O 2-) in the CaO-SiO2-MnO system by Xray photoelectron spectroscopy (XPS) and found that the silicate melts were depolymerized by addition of MnO at a fixed CaO/SiO2 ratio. Recently, Park et al [42][43][44] unveiled that the sulfide capacity of the CaO-SiO2-MnO slag is strongly dependent on the effect of CaO and MnO on the depolymerization behavior of silicate networks. From these previous works, the quantitative information on the structure of the ISIJ International, Vol.…”

Sulfide Capacity and Excess Free Energy of CaO^|^ndash;SiO2^|^ndash;MnO Slag Derived from Structural Analysis of Raman Spectra

“…(5) In the present study, the activity coefficients of oxide components CaO, MnO and SiO2 was calculated using a commercial thermochemical computing software, FactSage TM 6.2 with 'FToxid' database, which has been successfully applied in computation of thermochemical properties of multicomponent oxide melts. 5,6,8,[13][14][15][16][17][18][19][20][21][22][23] Especially, the thermodynamic database for the CaO-SiO2-MnO system was fully optimized by Kang et al 24) Also, from the previous works by the present author, 5,6,8,18,19) the activity calculation in the present CaO-SiO2-MnO system was in good consistency with other thermochemical properties such as carbide capacity, sulfide capacity, etc.…”

“…basicity but also the effect of structural modification behaviour on the stability of oxygen and sulfide ions in silicate melts. 5,6,8) In previous works of the present author, 1,5,6,8) it was found that, in the relatively acidic region of which silica content is greater than about 30(±5) mass%, the large amounts of Ca 2+ ions are consumed to modify the silica networks due to a large ionic potential, resulting in a stabilization of S by Ca 2+ ions due to an interaction between Ca 2+ and S 2-ionic pair which is stronger than Mn 2+ and S 2-pair. The more details on this discussion are available in Refs.…”

Effect of Atmosphere and Slag Composition on the Evolution of PH3 Gas during Cooling of Reducing Dephosphorization Slags

“…However, the distribution ratio of phosphorous remained constant at CaO content greater than about 20 mass%, where the flux is saturated by solid lime from the CaO-CaF2 binary phase diagram, 20) indicating that the activity of free O 2-ions is approximately constant, assuming that is proportional to aCaO in the flux. [21][22][23][24][25][26][27][28] …”