Solubility Equilibrium of the NaOH–H₂O–Na₂CrO₄–Na₂SiO₃–NaAlO₂ Multicomponent Systems Involved in the Liquid-Phase Oxidation of Chromite

Chromium salts are a group of important chemical raw materials with many applications. While the conventional manufacturing process, i.e. calcium roasting of chromite, has many disadvantages; the novel processes of liquid-phase oxidation, whose main reaction is the oxidation of chromite by oxygen (air) in highly concentrated alkaline solutions, are promising to achieve clean manufacturing. For the oxidation reaction of chromite in NaOH solutions, a significant amount of multicomponent systems consisting NaOH, Na₂CrO₄, Na₂SiO₃, and NaAlO₂ are generated. It is a prerequisite to clarify the solubility equilibrium of the multicomponent systems for exploring highly efficient separation methods of Na₂CrO₄ with Na₂SiO₃ and NaAlO₂. In this paper, Na₂CrO₄ solubility in the ternary system of NaOH–H₂O–Na₂CrO₄ was first measured using the equilibrium analysis method and varying the NaOH concentrations from 100 to 800 g·L^–1 and the temperatures from 353.15 to 403.15 K. Aferwards, the solubility of Na₂CrO₄, NaAlO₂, and Na₂SiO₃ in the other multicomponent systems was analyzed at NaOH concentration = 400, 500, and 600 g·L^–1, respectively