Digestion behavior and removal of sulfur in high-sulfur bauxite during bayer process.

• The sulfur behavior has been clarified by thermodynamic analysis and experiments. • The sulfur concentration orders in liquor are as follows: S2− > SO 4 2− > SO 3 2− > S 2 O 3 2−. • The S2− can be removed completely by adding ZnO during digestion process. In this paper, digestion behavior and removal of sulfur in high-sulfur bauxite during Bayer process were studied. The thermodynamic analysis shows that pyrite reacts with alkali solution to generate different valence sulfur (S2−, S 2 O 3 2−, SO 3 2−, SO 4 2−), Fe 2 O 3 , and Fe 3 O 4 ; the standard Gibbs free energy of these reactions is negative and decreases with the increasing of temperature in range from 473 K to 573 K; the generation orders of different valence sulfur can be easily determined: S2− > SO 4 2− > SO 3 2− > S 2 O 3 2−. The digestion experiment researches indicated that sulfur in high-sulfur bauxite entered solution mainly in the form of S2−, the digestion rates of sulfur increased with the increase of temperature, which was consistent with our thermodynamic calculation results. Based on the digestion behavior of sulfur, an appropriate method of sulfur removal was proposed, the S2− which is the main form of sulfur in liquor can be removed completely by adding ZnO during digestion process. [ABSTRACT FROM AUTHOR]