Digestion behaviors of sulfur-containing minerals and desulfuration during alumina production process

Abstract

The pyrite and sulfate digestion behaviors and sulfur removal of high sulfur bauxite during Bayer process were studied in this paper. The thermodynamic analysis shows that pyrite reacts with alkali solution to generate different valence sulfur (S2-, S2O32-, SO32-, SO42-), Fe2O3, and Fe3O4; 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 order of different valence sulfur is easily determined: S2-﹥SO42-﹥SO32-﹥S2O32-; the gypsum reacts with sodium aluminate solution to generate SO42- and Ca(OH)2. The digestion experiment researches indicates that pyrite and sulfate enter solution mainly in the form of S2- and SO42- respectively, the Fe2O3 and Fe3O4 are also found in red mud, experiment results are consistent with our thermodynamic calculation results. Based on the digestion behaviors of pyrite and sulfate, we propose appropriate methods of S2- and SO42- removal. The S2- which is the main form of sulfur in digestion liquor A was removed completely by adding ZnO in digestion process, and the SO42- which is the main form of sulfur in digestion liquor B was removed completely by adding BaO·Al2O3. The results may throw a new light upon the sulfur removal of high-sulfur bauxite in alumina production.