Thermodynamic Research of S-H<sub>2</sub>O System in Sodium Aluminate Solution

There are many different types of valence of sufur in aluminate sodium solution during the process of the bauxite dissolution, which mainly including S2-, S22-, S, S2O32-, SO32-, SO42- and it may have an effect on the mineral dissolution process. Therefore, it is necessary that the thermodynamic properties of S-H2O system were investigated in sodium aluminate solution. In this paper, the reactions between different valence states of sulfur and lye (with or without oxygen participation) were studied in sodium aluminate solution. The thermodynamic software Factsage 7.0 was carried out to calculate the standard reaction Gibbs free energy (ΔGTθ). The results showed that S2- and SO42- are the most stability in terms of the autoreactive reaction of different valence states at 298-573 K, and that the stability of different valence states of sufur order is “S22- >(S2O32-, SO32-) >S”. At 523 K, SO32- is more stable than S2O32-. On the other hand, the low-valent sulfur was more likely to be oxidized into SO42- under oxidizing conditions at 298-573 K. Besides, it was also found that S22- is most susceptible to oxidation because of the lowest stability. Finally, the stability of the other valence states of sulfur under oxidizing conditions order is “SO32- >S2O32- >S2- >S”.