Transport properties of dissolved [O] in the (LiF–CaF2)eut.–NdOF molten salt system

Abstract

The transport properties of [O] in dissolved rare-earth oxyfluorides provide an important theoretical basis for optimizing anode reactions during molten salt electrolysis in fluoride systems for rare-earth metal production. In this study, the solubility of NdOF in (LiF–CaF₂)_eut. was investigated, and the electrical conductivity and density of the saturated NdOF system were measured. The self-diffusion coefficients and radial distribution functions of the ions in the system were analyzed using first-principles molecular dynamics. The transport number of dissolved O*(II) ions in the saturated (LiF–CaF₂)_eut.–NdOF system was determined using the coulometric method, providing a comprehensive analysis of the variation in the migration rate and diffusion coefficients of dissolved O*(II) ions. The results showed that the solubility of NdOF in the (LiF–CaF₂)_eut. System, along with the electrical conductivity and density of the saturated system, exhibited linear variations in the temperature range of 1123–1373 K. The transport number, migration rate, and diffusion coefficient of dissolved O*(II) ions underwent non-linear changes with increasing potential within the range of 3.0–4.5 V, reaching a maximum in the range of 3.75–4.25 V, while still increasing linearly with temperature. When the [temperature-potential] was in the [1200 K↑–3.5 V↑] range, the migration rate and diffusion coefficient of O*(II) ions were the highest, with the potential playing a dominant role in the diffusion coefficient of O*(II) ions. The radial distribution function values of the ions in the system indicated that Nd*(III) ions had the strongest restraining effect on the dissolved O*(II) ions during the diffusion process.