Vaporization of Na and S from Sodium Silicate Slags

Abstract

In relation to hot metal pretreatment by soda ash, the vaporization of Na and S from sodium silicate slags has been investigated. At temperatures between 1623 and 1773 K, the slag was melted in a graphite crucible under an atmosphere of argon. The amount of Na and S generated was determined by thermogravimetry and chemical analysis.
The rate of Na vaporization from Na₂O-SiO₂ slag is approximately represented by the first-order-type rate equation. The rate constant increases with increasing slag basicity, i.e. the (%Na₂O)/(%SiO₂) ratio, and the activation energy varies from 230 to 250 kJ/mol. It is considered that the vaporization would be controlled by the chemical process.
Both Na and S evaporate from Na₂O-SiO₂ slags containing Na₂S. Particularly in the acid slag, the most of the mass loss measured is due to the vaporization of Na₂S. The vaporization of S is retarded by an increase in the slag basicity, but the reduction of Na₂O at an early stage is accelerated by the addition of Na₂S to the high basic slag.