The knowledge of sulfide capacities of FeO-containing slags is necessary for better understanding the resulfurization reaction in hot metal pre-treatments. In this study, copper-iron-sulfur liquid ...alloy was equilibrated with CaO–SiO2–FeO ternary slag to measure sulfide capacities and FeO activities simultaneously at temperature below the melting point of pure iron. The experimental result that the sulfide capacity increased with increasing FeO content could be explained by the fact that FeO was a basic oxide, and the sulfide capacity of the CaO–SiO2–FeO ternary system was significantly larger than those of the CaO–SiO2–MgO, CaO–SiO2–AlO1.5 and CaO–SiO2–CaF2 ternary systems. Although the FeO activity and oxygen potential were raised by the FeO addition, the calculated value for sulfur distribution ratio between CaO–SiO2–FeO slag and hot metal increased with an increase in FeO content.
The solubility of sulfur as S2– has been experimentally determined for 19 silicate melt compositions in the system CaO–MgO–Al2O3–SiO2(CMAS) ± TiO2 ± FeO, at 1400°C and 1 bar, using CO–CO2–SO2 gas ...mixtures to vary oxygen fugacity (fO2) and sulfur fugacity (fS2). For all compositions, the S solubility is confirmed to be proportional to (fS2/fO2)1/2, allowing the definition of the sulfide capacity (CS) of a silicate melt as CS = S(fO2/fS2)1/2. Additional experiments covering over 150 melt compositions, including some with Na and K, were then used to determine CS as a function of melt composition at 1400°C. The results were fitted to the equation \batchmode \documentclassfleqn,10pt,legalpaper{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\hbox{C}_{S} = \hbox{A}_{0}+\displaystyle{\sum_{M}}\hbox{A}_{M}\hbox{X}_{M}+\hbox{B}_{Fe-Ti}\hbox{X}_{Fe}\hbox{X}_{Ti}\) \end{document}, where AFe ≫ ACa > AMg,ANa/K,ATi. The FeO content of natural basalts is the dominant control on CS. The equation for CS was then combined with the equation for the thermodynamic equilibrium between silicate melt and immiscible FeS-rich sulfide melt, to develop an expression for the sulfur content at sulfide saturation (SCSS) of the silicate melt. The value of SCSS is independent of fO2 and fS2, but shows an asymmetric U-shaped dependence on the FeO content of the silicate melt. Many of the experiments on Fe-containing melt compositions were saturated with immiscible FeS melt, and these experiments were used to calibrate quantitatively SCSS at 1400°C as a function of melt composition.
An inclusion compound of Ca12Al14O33 has been reported as a solid oxide having high sulfide capacity. Towards better understanding of the substitution reaction of S2− for clathrated O2− in ...Ca12Al14O33, in this study, the inclusion compounds were equilibrated under fixed O2/S2 partial pressure ratios at 1573 K. It was founded that the sulfide capacity of solid Ca12Al14O33 was higher than that of the homogeneous CaO–Al2O3 liquid and decreased with an increase in the sulfur content. When the sulfur-substituted inclusion compound was regarded as the Ca12Al14O33–Ca12Al14O32S solid solution, the Ca12Al14O33 and Ca12Al14O32S activities exhibited Raoultian behaviors. Furthermore, the standard Gibbs energy change for the following substitution reaction was determined.Ca12Al14O33+(1/2)S2(gas)=Ca12Al14O32S+(1/2)O2(gas)ΔG∘=68.2 kJ⋅mol-1 at 1573 K
The effect of TiO2 content ranging from 0 wt% to 4 wt% on the viscosity and sulfide capacity of CaO–SiO2–MgO–Al2O3–BaO–TiO2 slag system was investigated using the rotating spindle method and gas-slag ...equilibration technique, respectively. The measured sulfide capacity was further compared with the predicted values by some empirical models based on the corrected optical basicity when the effect of charge compensation effect of Ba2+ and Ca2+ was considered. The results show that the viscosity declines with TiO2 content increasing while keeping CaO/SiO2 ratio and other components contents constant, and TiO2 seems to be more effective in decreasing viscosity when polymerization degree of slag is higher. The sulfide capacity decreases with an increase in TiO2 content although the dynamic condition is improved due to the viscosity decreasing. The sulfide capacity is enhanced with the increasing corrected optical basicity and it can be predicted by using the modified predicted values based on Zhang’ model.
To clarify the mechanism of CaS formation on the oxide inclusion of the CaO–Al2O3 system, the sulfide capacities of solid oxides was measured in the present study. The results show that the sulfide ...capacity of (12CaO·7Al2O3; C12A7) was much larger than of other compounds, and increased with temperature. The value for C12A7 was larger than that measured for the liquid oxide of the same composition. Furthermore, the diffusion behavior of sulfur in solid steel to the inclusion of the CaO–Al2O3 system, was investigated using a diffusion couple. After heating at 1473 K for 72 h, in the case of C12A7, the intensity of sulfur in the oxide was high, but the formation of CaS was not detected. This suggests that the formation of CaS was suppressed around the C12A7 particles by the diffusion of sulfur in the solid oxide.
To clarify the mechanism of CaS formation on the oxide inclusion of the CaO–Al2O3 system, the sulfide capacities of solid oxides was measured in the present study. The results show that the sulfide ...capacity of (12CaO·7Al2O3; C12A7) was much larger than of other compounds, and increased with temperature. The value for C12A7 was larger than that measured for the liquid oxide of the same composition. Furthermore, the diffusion behavior of sulfur in solid steel to the inclusion of the CaO–Al2O3 system, was investigated using a diffusion couple. After heating at 1473 K for 72 h, in the case of C12A7, the intensity of sulfur in the oxide was high, but the formation of CaS was not detected. This suggests that the formation of CaS was suppressed around the C12A7 particles by the diffusion of sulfur in the solid oxide.
Modeling the effect of H2O on the “sulfur content at sulfide saturation” (SCSS) in silicate melt is essential for the estimation of SCSS in both arc magmas and slab melts. Here we present a ...thermodynamic approach, in which, SCSS in hydrous silicate melt has been modeled as a combination of S dissolving as S2− and HS−/H2S, based on the sulfide capacity (CS2−) and the hydro-sulfide capacity (CHS), respectively. By adopting the thermodynamic framework of O’Neill and Mavrogenes (2002), S dissolution as HS−/H2S can be modeled in an analogous fashion to that for modeling S2− in anhydrous melt with the relation: lnHSSCSS=-ΔG°Fes-FeO/RT+lnCHS-lnaFeOmelt+lnaFeSsulfide. To obtain an expression for CHS, we compiled published experimental data on SCSS in hydrous silicate melts covering a PT range of 0.15–3 GPa and 785–1600 °C, and melt H2O contents of ∼1–13 wt%. While the contribution of S dissolving as S2− in basaltic and andesitic melts can be calculated based on the updated SCSS model for anhydrous basic melt from O’Neill (2021), S2− is considered negligible in rhyolitic and dacitic melts, i.e., when melt FeO content <∼5 wt%. We propose an expression for CHS as a function of temperature, mole fractions of cations for the normalized anhydrous melt composition, ln(XOH + XH2O), and a Na + K-Al term for alkaline-enriched rhyolitic melts. The coefficients for cation mole fractions are adopted from the expression for CS2− from O’Neill (2021); the coefficients for the 1/T and Na + K-Al terms are obtained from regression. The reproducibility of compiled SCSS values is ±50% for hydrous rhyolitic and dacitic melts, and ±10–30% for hydrous basaltic and andesitic melts, representing a significant improvement in comparison to previous models.
Our model produces SCSS values for the primitive arc magmas compiled by Ruscitto et al. (2012), that are in most cases higher than the measured S contents, implying sulfide under-saturated conditions during mantle wedge melting. The contribution of H2S dissolution to the calculated SCSS values varies in a range of 70–1234 ppm, which increases with the increase of H2O content (0.3–6.2 wt%). H2S dissolution therefore contributes to the higher S content in arc basalt compared to MORB, an observation which is further corroborated by the positive correlation between H2O and S contents in primitive arc magmas. Applying our current model to experimentally produced sediment melts spanning a PT range of 690–1050 °C and 2.5–4.5 GPa, demonstrates that sediment melts, especially those of intermediate supercritical character with >25 wt% H2O and peralkaline in composition, can have high SCSS values as a result of H2S dissolution, and act as the transfer medium for S recycling between the slab and mantle wedge under reduced conditions.
To improve the desulfurization in the COREX-3000 process, several aspects are studied and practiced. The work documented in the present paper focuses on the effects of chemical compositions of slag, ...such as CaO/SiO2, MgO, MgO/Al2O3 and MnO, on desulfurization. Theoretical calculations of sulfide capacity and viscosity of slag and diffusion coefficient of S2− in the slag are given to study the effects of slag chemical compositions on the thermodynamics and dynamics of desulfurization. After that, experiments are carried out to verify the theoretical analyses and give the appropriate ranges of these four parameters. The suggested suitable ranges of CaO/SiO2, MgO content, MgO/Al2O3 and MnO content for COREX-3000 are 1.20–1.30, 10 wt%–12 wt%, 0.80–0.90 and 0.4 wt%–0.7 wt%, respectively.
The desulfurization behavior of 316L stainless steel (STS316L) melt with the CaO-SiO2-CaF2-Al2O3-MgO slag was investigated with different CaO/SiO2 (=C/S) ratio and CaF2 content at 1873 K. As the C/S ...ratio increased, the sulfide capacity increased, whereas the sulfide capacity of the high C/S (=1.7) slag was not affected by CaF2 content. The overall mass transfer coefficient (kO) increased with C/S ratio, but was constant above a critical C/S value, and it was also constant across varied CaF2 content at relatively high C/S (=1.7) condition. Since the metal condition of the present study was constant, the change in kO was caused by slag phase mass transfer coefficient (ks) and sulfur distribution ratio (LS), which were affected by the physicochemical properties of the slag. Since desulfurization reaction requires consideration of both kinetic and thermodynamic factors, the ‘logCS2−−logη’ (where CS2− is sulfide capacity and η is viscosity), was proposed as a meaningful physicochemical parameter. If the slag basicity is relatively high, at which the kO is equivalent regardless of slag compositions, the desulfurization reaction is controlled by metal phase mass transfer. However, if the slag basicity becomes lower, at which the kO significantly decreases, the desulfurization reaction is assumed to be controlled by slag phase mass transfer and/or mixed controlled process.
The desulphurisation of blast furnace slag is an important metallurgical function of blast furnace smelting. To elucidate the desulphurisation behaviour of blast furnace slag with high Al
2
O
3
...content, the slag-metal equilibrium method was employed to determine the sulfide capacity (C
S
) of CaO-SiO
2-
Al
2
O
3-
MgO melts for blast furnace smelting at 1823 K. When basicity (R
w
=w(Basic oxide)/w(Acid oxide)) and w(MgO)/w(Al
2
O
3
) were increased, the intensities of the characteristic peaks of SiO
4
and AlO
4
in Raman spectrum decreased, indicating that the degree of polymerisation had reduced. The cluster structures of SiO
4
and AlO
4
depolymerised and lgC
S
(i.e. the desulphurisation ability) increased, owing to which the number of free O
2−
ions increased. However, when w(Al
2
O
3
) was increased, the intensities of the characteristic peaks of SiO
4
and AlO
4
in Raman spectrum increased gradually, indicating that the degree of polymerisation had increased, and the simple structures of SiO
4
and AlO
4
were polymerised. As a result, both the number of free O
2−
ions and lgC
S
decreased.
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