Solubility of Nickel Ferrite in High-Temperature Pure or Oxygenated Water

The solubility of nickel ferrite is measured at 423, 473, and 523 K in a pure or oxygenated water system, which is similar to boiling water reactor conditions‚ using a specially designed batch autoclave system. Thermodynamic analysis is performed by a procedure minimizing Gibbs free energy of the system at the final state. On the basis of both the analysis and the experimental results, it is shown that the dissolution mechanism of NiFe₂O₄ under the condition where no redox reaction takes place consists of both NiFe₂O₄ dissolution and Fe₂O₃ precipitation equilibria. The calculated value of the solubility at 423 K using literature values of the thermodynamic data agree with the experimental value, but at 473 and 523 K they deviate somewhat from the experimental ones. By fitting to the experimental results at these temperatures, the thermodynamic data of NiFe₂O₄ for 473 and 523 K are reanalyzed, and new values are proposed.