Abstract:Thermodynamic diagrams of Na-S-Fe-H₂O system were constructed to analyze the behavior of sulfur and iron in the Bayer process. After digestion, iron mainly exists as Fe₃O₄ and Fe₂O₃ in red mud, and partial iron transfers into solution as Fe(OH)₃^-, HFeO₂^-, Fe(OH) ₄^- and Fe(OH)₄^2-. The dominant species of sulfur is S^2-, followed by SO ₄^2-, and then SO ₃^2- and S₂O ₃^2-. The thermodynamic analysis is consistent with the iron and sulfur species distribution in the solution obtained by experiments. When the temperature decreases, sulfur and iron can combine and precipitate. Controlling low potential and reducing temperature are beneficial to removing them from the solution. XRD patterns show that NaFeS₂·2H₂O, FeS and FeS₂ widely appear in red mud and precipitates of pyrite and high-sulfur bauxite digestion solution. Thermodynamic analysis can be utilized to guide the simultaneous removal of sulfur and iron in the Bayer process.

Key words: high-sulfur bauxite; Na-S-Fe-H₂O system; thermodynamic analysis; simultaneous removal; sulfur; iron; Bayer process