Role of Dissolved Oxygen in Iron Oxidation in Supercritical Water: Insights from Reactive Dynamics Simulations

Oxygenated treatment is considered to be an effective chemical water treatment method and is widely used in supercritical power plants. Previous isotope tracer experiments reported that dissolved oxygen and supercritical water (scH(2)O) react with metals simultaneously, but the atomistic mechanism remains unrevealed. We performed reactive dynamics simulations to investigate the role of dissolved oxygen in iron oxidation in supercritical water. Structural analysis shows that the prior reacted O from O-2, (O-xy) will activate the surface Fe atom to react with the O in scH(2)O (O-wa), resulting in a Fe-O-xy-Fe-O-wa-H structure. Aside from activating Fe, O-xy has another contribution of absorbing the proton generated after the dissociation of scH(2)O. These two roles of dissolved O-2 result in an O-2-boosted scH(2)O oxidation mechanism. A series of simulations indicate that appropriate O-2 concentration will accelerate the formation of the surface protective oxide layer, whereas excessive O-2 concentration might cause destructive internal oxidation of Fe. The increase of temperature has little influence on the formation of the surface oxide layer but will increase the internal oxidation rate of O-2.