Fundamental Studies on Recovery of Na₂CO₃ from the Sodium Containing Slag

Abstract

Chemical reactions for the recovery of Na₂CO₃ from the slag obtained in the refining of hot metal with Na₂CO₃ were studied. The process for the Na₂CO₃ recovery consisted of three main unit operations.
1) Dissolving of the slag in the circulating aqueous solution.
2) Removal of residue and impurities (Si, P) from the solution.
3) Recovery of Na₂CO₃ from the solution.
More than 90% of Na, P, V and 40 to 50% of S, Si contained in the slag dissolved in the solution and main ion species in the solution were proved as Na⁺, V⁵⁺, OH^-, CO^2-₃, SiO^2-₃, PO^3-₄, S^2-, S₂O^2-₃and SO^2-₄. With the addition of CO₂, OH^-/CO^2-₃ ratio in the solution turned to nil and Si concentration in the solution reduced to 2g/l because of hydrolysis of SiO^2-₃ ion. Addition of Ca(OH)₂ in the solution caused reduction of P concentration to less than 3g/l, due to the formation of Ca₃(PO₄)₂·Removal of V and S ion were also studied. From these experiments, a process-flow for the Na₂CO₃ recovery from the slag was proposed.