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

Abstract

KEY WORDS: silicate structure; Raman spectroscopy; sulfide capacity; excess free energy of mixing; Q 3 /Q 2 ratio; degree of polymerization; free oxygen; bridging oxygen; non-bridging oxygen.In a previous article, 1) the structure of molten CaO-SiO 2 -MnO slag was systematically analyzed using micro-Raman spectroscopic data obtained from a melt-quenched glass samples. Various thermophysical properties such as viscosity, density (molar volume), and electrical conductivity (resistivity) of the CaO-SiO 2 -MnO slag was strongly dependent of a degree of polymerization defined as Q 3 /Q 2 ratio. Furthermore, the speciation of free oxygen, bridging oxygen and non-bridging oxygen was also quantitatively derived from a novel approach based on a mass balance of oxygen and silicon atoms in discrete silicate anionic units, viz. Q n (n = 0, 1, 2, and 3). In the present note, the thermochemical properties such as sulfide capacity and excess free energy of mixing of oxide components which are important properties in metallurgical slags are evaluated using a concentration of free oxygen as well as a degree of polymerization of silicate melts, i.e. Q 3 /Q 2 ratio. The capability of molten slags absorbing sulfide ions is quantified as the sulfide capacity ( ) which is given in Eq. (2) where K (1) , , , , and p i indicate, respectively, the equilibrium constant of Eq. (1), the activity, mole fraction and activity coefficient of free oxygen ions as a reference to Raoultian standard state, the Henrian activity coefficient of sulfide ions, and the partial pressure of gaseous component i. Hence, the log will be directly proportional to the log , if the second term in Eq. (3) would not be significantly changed by silicate composition at a fixed temperature.The sulfide capacity of the CaO-SiO 2 -MnO slag measured by Abraham et al. 4) and Park et al. 5,6) is shown in Fig. 1 as a function of the concentration of free oxygen ions obtained in previous study. 1) Here, the relationship between the sulfide capacity and the content of free oxygen in the CaO-SiO 2 binary slag at 1 773 and 1 923 K is also compared.7) There is a good linear relationship with a slope of about 0.9 which is close to the ideal value of unity from Eq. (3) between log and log as given in Eq. (4) However, the sulfide capacity of the CaO-SiO2 binary slag at 1 923 K is above Eq. (4) at a given O 2-content, which probably results from the effect of temperature not only on the value of K(1) but also on the ratio. Consequently, it is concluded that the sulfur dissolution behavior into the silicate melts at high temperatures can be understood more quantitatively by considering not only the effect of concentration (or activity) of free oxygen ions, viz. 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+ ion...

Effect of CaF2 Addition on the Viscosity and Structure of CaO–SiO2–MnO Slags

“…The structural role of Ca 2+ and Mn 2+ ions in a depolymerization process of the CaO-SiO2-MnO ternary system was systematically discussed in our previous articles. [21][22][23] The viscosities of the CaO-SiO2-CaF2-10 mass% MnO system at various temperatures are plotted against the content of CaF2 in Fig. 6.…”

“…The details for the Gaussian deconvolution process are available in our previous works. [21][22][23] The fraction of Q 3 (Si2O5-sheet) unit is less than 10% and continuously decreases with increasing content of CaF2 and the fractions of Q 0 (SiO4-monomer) and Q 1 (Si2O7-dimer) units increase as the content of CaF2 increases.…”

“…The Q 3 /Q 2 ratio, which was originally proposed as a quantitative polymerization index of silicates in our previous works, [21][22][23] is plotted against CaF2 content in Fig. 14.…”

“…Recently, we thoroughly evaluated the novel structure-viscosity relationship of CaO-SiO 2 -MnO slag system using micro-Raman spectroscopy due to its importance in smelting and refining processes for the production of manganese ferroalloys as well as high manganese steels. 21,22) The slag-metal reaction kinetics should be enhanced in view of high production rate and low cost in smelting and refining processes of Mn ferroalloys as well as high Mn steels. In order to meet these requirements, it is necessary to consider and quantify the effect of fluorspar (CaF 2 ) addition on the viscosity of MnO-containing slags at high temperatures, because the CaF 2 is well known to decrease the viscosity of silicate melts.…”

“…In addition, the Raman spectra of the quenched glass samples were quantitatively analyzed to investigate the structural role of CaF2 in a depolymerization of silicate networks with a reference to our previous works. 21,22) 2. Experimental…”