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

Abstract

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.