Dissolution Rate and Diffusivity of Silica in SiMn Slag

Abstract

The dissolution rate and solubility of quartz in silicomanganese slag were studied in the temperature range of 1673 K to 1823 K (1400 °C to 1550 °C) under an inert atmosphere of argon. The dissolution rate of quartz was measured using a rotating rod technique; while quartz solubility was examined using static experiments. Solubility of silica in slags was also calculated using multi-phase equilibrium thermodynamic software developed by CSIRO. Effects of additives (CaO, MnO, SiO₂, and Al₂O₃) on the quartz dissolution rate and solubility were also examined. Under the experimental conditions employed the dissolution rate of quartz was controlled by mass transfer of silica in the slag. Silica diffusion coefficients in silicomanganese slag varied from 0.9 × 10⁻⁷ to 1.3 × 10⁻⁶ cm²/s, depending on temperature and slag composition. Activation energy for the diffusion of silica in silicomanganese slag was found equal to 367 kJ/mol. The addition of 10 wt pct CaO decreased activation energy to 115 kJ/mol, while addition of 10 wt pct Al₂O₃ increased the activation energy to 430 kJ/mol. Effect of slag composition on silica diffusivity was examined in relation with structure of molten slag.

Appendix

Calculation of NBO/T[9]

$$ \begin{aligned} Y_{\text{NBO}} & = & \sum {2[x({\text{CaO}}) + x({\text{MgO}}) + x({\text{FeO}}) + x({\text{MnO}}) + x({\text{Na}}_{2} {\text{O}}) + x({\text{K}}_{2} } {\text{O}})] \\ \quad + x({\text{MnO}}) + x({\text{Na}}_{2} {\text{O}}) + x({\text{K}}_{2} {\text{O}})] \\ \quad + 6(1 - f)x({\text{Fe}}_{2} {\text{O}}_{3} ) - 2x({\text{Al}}_{ 2} {\text{O}}_{3} ) \\ \quad - 2fx({\text{Fe}}_{2} {\text{O}}_{3} ), \\ \end{aligned} $$

$$ x_{\text{T}} = \sum {x({\text{SiO}}_{2} } ) + 2x({\text{Al}}_{2} {\text{O}}_{3} ) + 2fx({\text{Fe}}_{2} {\text{O}}_{3} ) + x({\text{TiO}}_{2} ) + 2x({\text{P}}_{2} {\text{O}}_{5} ), $$

$$ ({\text{NBO}}/{\text{T}}) = \left( {{\raise0.7ex\hbox{${Y_{\text{NB}} }$} \!\mathord{\left/ {\vphantom {{Y_{\text{NB}} } {x_{\text{T}} }}}\right.\kern-0pt} \!\lower0.7ex\hbox{${x_{\text{T}} }$}}} \right), $$

where x = mol fraction,

$$ f = {\text{Fe}}^{3 + } ({\text{IV}})/({\text{Fe}}^{3 + } ({\text{IV}}) + {\text{Fe}}^{3 + } ({\text{VI}})). $$