Effect of Salt Deposits on Corrosion Behavior of Ni-Based Alloys in Supercritical Water Oxidation of High-Salinity Organic Wastewater

In this study, the corrosion behavior of nickel-based alloys 625, 825, and 800 with a salt deposit layer was investigated in supercritical water containing a dissolved oxygen of 5,000 ppm at 400°C. Scanning electron microscopy, energy-dispersive spectroscopy, atomic force microscope, X-ray diffraction, and laser Raman spectroscopy were used to investigate the morphologies and compositions of samples. Control experiments were performed to investigate the effects of a salt deposit layer. The presence of one salt deposit layer on the sample surface resulted in the occurrence of an acidic and oxidizing microenvironment between the alloy surface and the salt deposit layer, evidently enhancing the corrosion of nickel-based alloys. A comparison of the corrosion resistances among Alloys 825, 800, and 625 indicated that Alloy 825 is the best. Additionally, a suggestion for materials selection in supercritical water oxidation plants for high-salinity organic wastewater treatment was proposed.