Photochemical Corrosion Inhibition of Mild Steel in Acid Mine Water

Abstract The corrosion inhibition of mild steel in acid mine water of pH 2.5 containing ferric and cupric ions with inhibitors such as urea ([NH2]2CO), guanylurea sulfate (C4H12N8O2·H2SO4), benzotriazole (C6H5N3), butylamine (C4H11N), hexadecyl pyridinium chloride (C21H38ClN·H2O), thiourea (CH4N2S), and potassium oxalate (K2C2O4·H2O) was studied. Thiourea and potassium oxalate gave 77% and 93% inhibition, respectively. Thiourea reduced ferric ions in solution and produced a sulfide film that caused hydrogen embrittlement. Corrosion inhibition by potassium oxalate was photosensitive due to the formation of a trisoxalato iron complex followed by photodecomposition to β-ferrous oxalate and its deposition on the steel sample, thereby inhibiting the corrosion of the steel. The mechanism of this first example of photochemical inhibition is postulated.