Dissolution Mechanism of Indium in CaO-Al2O3-SiO2 Slag at Low Silica Region

2012

ISIJ Int.

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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...

mentioning

confidence: 64%

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

2012

ISIJ Int.

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“…The activity of each component in slag phase was calculated by commercial thermochemical computing program, FactSage6.2™ with “FToxid” database (mailto:basicity@hanyang.ac.kr). This database was successfully used for the estimation of the thermodynamic properties of oxide systems through a wide temperature and composition range 1, 6, 11–25…”

Section: Methodsmentioning

confidence: 99%

Competitive Dissolution Mechanism of Sulfur in CaMnSilicate Melts: Structural View

2013

steel research int.

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The sulfide capacities of the CaO-SiO 2 -MnO(-Al 2 O 3 -MgO) slags were measured at 1873 K over a wide composition range using a gas-slag equilibration method. The effects of MnO content and the MnO $ CaO substitution 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 wt%), the sulfide capacity mainly increased with increasing MnO content. Also, the sulfide capacity and the activity of MnO showed a linear relationship with a slope of unity, indicating that MnO is dominant component controlling the sulfur dissolution behavior into Ca-Mn-silicate melts. The sulfide capacity increased as MnO substituted for CaO in the high silica melts (>30 (AE5) wt% SiO 2 ), whereas it decreased by increasing the MnO/CaO ratio in the low silica melts (<30(AE5) wt% SiO 2 ). This tendency of sulfide capacity resulted in the clockwisely rotating iso-capacity contours from MnO-free side to MnO-rich corner in Ca-Mn-silicate melts. The dissolution mechanism of sulfur in Ca-Mn-silicate melts can be explained by the ''Competitive dissolution mechanism.''

“…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] …”

Section: Thermodynamics Of Reducing Dephosphorizationmentioning

confidence: 99%

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

Shin

2013

ISIJ Int.

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The distribution ratio of phosphorous between the CaO-CaF2 (-SiO2) flux and SiMn alloy melts at 1 823 K was measured under strongly reducing atmosphere. Furthermore, thermodynamic and kinetics analyses were carried out for the environmental stability of reducing refining slags containing Ca3P2 under wet cooling conditions from the effect of slag composition on the evolution of PH3 (phosphine) gas. The distribution ratio of phosphorous between the CaO-CaF2 (-SiO2) flux and SiMn metal phases increased with increasing CaO concentration in the flux, followed by a constant value. The composition for the saturating distribution ratio of phosphorous was in good accordance to the saturation content of CaO in the CaOCaF2 flux at 1 823 K. When the Vee ratio (= CaO/SiO2) of the dephosphorization slag was greater than about 1.35, the lime and dicalcium silicate phases precipitated during solidification, resulting in an increase in the evolution rate of PH3 gas under wet and dry conditions due to an increase in the reaction area. However, when the Vee ratio of the slag was lower than about 1.35, fluorite, cuspidine, and wollastonite phases precipitated from the phase diagram, resulting in less amount of PH3 evolution during cooling because the reaction between Ca3P2 and H2O was restricted to the surface of bulk slag.