Decomposition of Sodium Carbonate and Its Mixture with Silica by Heating and Carbon-Reduction

Abstract

The decomposition rate of Na₂CO₃ melts in the temperature range from 1 200 to 1 700°C under argon atmosphere was measured by using a thermobalance. Significant weight loss of the melt was observed adove 1 300°C. The rate at a steady state was given as ω=9.66 × 10² exp (- 58 600/RT) (g/cm²·). The reaction scheme was concluded from this equation to be Na₂CO₃(l)→ Na₂O(l) + CO₂(g), Na₂O(l) → 2Na (g) + 1/2O₂(g). The rate-determining step was the diffusion of reaction products in argon.
The reduction of premelted Na₂CO₃-SiO₂ mixtures with graphite at about 1 200°C was examined. Residual Na₂CO₃ in the premelted mixture was completely decomposed by the reaction: Na₂CO₃(l) + 2C(s) → 2Na(g) + 3CO(g). No substantial reduction was observed for sodium metasilicate, Na₂O· SiO₂, dissolved in the premelted mixture. Excess Na₂O over 1 mol per 1 mol SiO₂ was decomposed by carbon: Na₂O(l) + C(S) → 2Na(g) + CO(g). Dense fume rising in the reaction furnace was observed during the reaction with graphite. This fume would be originated from the sodium vapour produced as the reaction product in the above reaction.
Some experimental results were presented on the removal of carbon dissolved in liquid iron by Na₂CO₃-SiO₂ mixtures.