SOLUBILITY OF NICKEL FERRITE IN HIGH-TEMPERATURE PURE OR OXYGENATED WATER

The solubility of nickel ferrite is measured at 823, 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 f ree energy of the system at the final state. On the basis of both the analysis and the experimental results, it is shown that the dissolutio n mechanism of NiFe2O4 under the condition where no redox reaction fak es place consists of both NiFe2O4 dissolution and Fe2O3 precipitation equilibria. The calculated value of the solubility at 423 K using lite rature values of the thermodynamic data agree with the experimental va lue, but at 473 and 523 K they deviate somewhat from the experimental ones. By fitting to the experimental results at these temperatures, th e thermodynamic data of NiFe2O4 for 473 and 523 K are reanalyzed, and new values are proposed.