Constructing the Pourbaix diagram of Fe-Cl−-H2O ternary system under supercritical water conditions

ABSTRACT Supercritical water oxidation (SCWO) technology, which has outstanding performance, is impeded commercial development due to serious corrosion problems. In this work, the first Pourbaix diagrams of the Fe-Cl−-H2O ternary system under supercritical water conditions was established to predict the evolution process of metals in thermodynamics equilibrium. The fifteen species were rationally screened by the ion distribution coefficient, and thermodynamics parameters under supercritical conditions were calculated by the extrapolation method of the revised Helgeson-Kirkham Flowers (R-HKF) model. The results show that hematite and magnetite passivation film and ferrous iron are continuously eroded by FeCl3 (aq) corrosion zone with the increase of chloride concentration, which greatly expands the area. Interestingly, the range of the immunization zone is almost unchanged. On the other hand, most of the Fe(OH)- 3 corrosion zone, passivation zone, and immunization zone to be converted to ferrous iron caused by temperature rise when FeCl3 (aq) reaches a certain concentration. Metals often form a hematite and magnetite passivation film to reduce the dissolution rate of the substrate under alkaline conditions with relatively high potentials, so the pre-neutralization method can be used as an anti-corrosion measure.