Effects of $${{{S}}^{{{2} - }}}$$- and $${{S_2}O_3^{2 - }}$$-Containing Bayer Solutions on Corrosion of 16Mn Low-Alloy Steel at Elevated Temperatures

Serious pipe corrosion caused by accumulated $${\text{S}}^{{{2} - }}$$ in Bayer solutions occurs when treating high-sulfur diasporic bauxite by the Bayer process at elevated temperatures. The effects of $${\text{S}}^{{{2} - }}$$ and $${\text{S}}_{{2}} {\text{O}}_{{3}}^{{{2} - }}$$ anions on the corrosion behavior of 16Mn low-alloy steel have been investigated under simulated high-temperature Bayer digestion conditions. The structure of the corrosion layers was analyzed. Results show that $${\text{S}}^{{{2} - }}$$ anions markedly accelerate such corrosion because of the generation of loose FeS-containing corrosion product, whereas $${\text{S}}_{{2}} {\text{O}}_{{3}}^{{{2} - }}$$ anions with concentration > 8.7 g L−1 can remarkably retard the corrosion process by forming a compact magnetite layer with dense and fine particles. Corrosion surface topography analyses support all the experimental corrosion results. Thus, $${\text{S}}_{{2}} {\text{O}}_{{3}}^{{{2} - }}$$ represents an effective corrosion inhibitor for 16Mn low-alloy steel, and $${\text{S}}^{{{2} - }}$$ to $${\text{S}}_{{2}} {\text{O}}_{{3}}^{{{2} - }}$$ transformations may contribute to preventing equipment corrosion when using high-sulfur bauxite in the Bayer process.