Chemical interactions between zirconium and free oxide in molten fluorides

Abstract

The chemical interactions between zirconium and free oxide in FLiNaK melts at different zirconium to oxide (n_Zr/n_O) molar ratios were studied by means of a carbothermal-reduction technique (LECO oxide analyzer) and Raman spectroscopy. ZrO₂ precipitates were formed with n_Zr/n_O ≤ 0.5, while ZrO₂ was converted to Zr₂OF_x^6−x complexes with n_Zr/n_O > 0.5. The maximum amount of Zr₂OF_x^6−x complexes in FLiNaK melts was found to be 0.020 mol kg⁻¹. With an initial oxide concentration lower than 0.020 mol kg⁻¹ and the required amount of ZrF₄, the free oxide in FLiNaK melts could be completely converted to Zr₂OF_x^6−x complexes, which would further prevent the formation of UO₂ precipitates.