Characterization of Material Corrosion in Sub/Supercritical Aqueous Dye Wastewater Environments

With increasing societal development, the consumption of printed and dyed fabrics has increased. The amount of wastewater produced by the printing and dyeing industry in this process is also increasing. Owing to the limitations of traditional treatment technology, this wastewater cannot be fully treated to achieve a benign state. Supercritical water oxidation technology has been recognized as a terminal technology with market prospects for the efficient and green treatment of hazardous organic waste. Nevertheless, the reactor used for supercritical water oxidation involves high-temperature, high-pressure, and high-oxygen environments. Therefore, this work explores the corrosion behavior of stainless steel 316L and nickel-based alloys Incoloy 800, Incoloy 825, and Inconel 625 under sub/supercritical aqueous anoxic conditions and supercritical aqueous oxidative conditions, as well as under the alkaline pH conditions of dye wastewater environments. The corrosion rates of stainless steel 316L, Incoloy 800, and Inconel 625 in subcritical water without oxygen were 0.073, 0.043, and 0.017 mm year^-1, respectively, at pH = 10. In comparison, the corrosion rate in an alkaline environment was only 0.072 mm·year^-1, and Inconel 625 was recommended for use in the project. Inconel 625 was recommended for use in the reaction phase of the continuous supercritical water oxidation system for dye wastewater treatment. Adding alkali to regulate the pH of wastewater can reduce the acidity of the wastewater, thus reducing the overall degree of corrosion of materials in the supercritical aqueous oxidative environment. When the pH was changed from 4 to 10, the corrosion rate of stainless steel 316L, Incoloy 800, Incoloy 825, and Inconel 625 changed from 0.466, 0.241, 0.233, 0.128 mm year^-1 to 0.311, 0.233, 0.128 mm year^-1, respectively, and the corrosion rates of stainless steel 316L, Incoloy 800, Incoloy 825, and Inconel 625 changed to 0.311, 0.210, 0.202, and 0.072 mm year^-1.