Interaction of Nickel Ions with Magnetite Particles in High-Temperature Water

The current study addresses the needs for deeper understanding of the behavior of iron-nickel based corrosion product systems, particularly the mechanism of ion/oxide interaction, formation and dissolution of nonstoichiometric nickel ferrites, which are believed to be the key targets of the activity transport in the primary circuits of light water reactor systems. The interaction of Ni²⁺ ions with Fe₃O₄ particles was studied experimentally in the aqueous phase at 423 and 473 K by monitoring the concentrations of nickel and iron ions in the aqueous phase after the injection of nickel ion solutions to the magnetite particle dispersion system. Formations of NiO or NiFe₂O₄, as initial metastable states, depending on the amount of the injected Ni²⁺ ions, were observed in the experimental series. A systematic understanding of the interaction mechanism was achieved based on the methods of both the thermodynamic analyses and solid-state diffusion. A new approach was proposed to treat a set of metastable states of the system tending to reach its most stable equilibrium state under a given initial condition. It was concluded from the experimental results and the thermodynamic analyses that the formed systems are gradually transforming through changing their composition and number of solid phases to the most stable state defined only by one solid phase, Ni_xFe_3−xO₄.