Solubility of Zinc Silicate and Zinc Ferrite in Aqueous Solution to High Temperatures

Crystalline zinc silicate, Zn2SiO4, and zinc ferrite, ZnFe2O4, were prepared and characterized. The solubilities of these phases were measured using flow-through apparatus from 50 to 350 °C in 100 °C intervals over a wide range of pH. Both solid phases dissolve incongruently, presumably to form ZnO(s) and Fe2O3(s) (or the corresponding hydroxide phases at low temperature), respectively. The respective concentrations of zinc(II) and iron(III) matched those of ZnO(cr) and Fe2O3(s) (≥150 °C) reported in the literature, whereas the corresponding Si(IV) and Zn(II) concentrations were at least an order of magnitude below the solubility limits for their pure oxide phases. Therefore, the solubility constants for zinc silicate and ferrite were determined with respect to the known solubility constants for ZnO(cr) and Fe2O3(s) (≥150 °C), respectively, and the corresponding concentrations of Si(IV) and Zn(II) measured in this study. The results of independent experiments, as well as those reported in the literature provide insights into the mechanism(s) of formation of zinc silicate and ferrite in the primary circuits of nuclear reactors.