Corrosion Studies in Kraft White Liquor: Potentiostatic Polarization of Mild Steel in Caustic Solutions Containing Sulfur Species^*

The corrosion of mild steel in kraft chemical pulping equipment has been investigated by laboratory electrochemical testing in relevant caustic solutions. Potentiostatic polarization curves were obtained in alkaline electrolytes with additions of sulfur containing compounds known to exist in process liquors. By observing the relative effects of individual sulfur species, it was possible to infer their respective contributions to the corrosion of steel in kraft white liquor. Sulfide and thiosulfate ions were both found to impair the ability of steel to passivate, and hence could be described as corrosion activators. Sulfite and sulfate ions had no effect. Polysulfide ions control the corrosion potential.