Time dependent chlorination of CeO2, La2O3 and Nd2O3 by ZrCl4 dissolved in eutectic LiCl–KCl

Partial chlorination of CeO2, La2O3, and Nd2O3 was achieved using ZrCl4 dissolved in molten LiCl–KCl at 450 °C over a period of 4–5 h. ZrCl4 was pre-volatilized into an argon stream to maintain a constant vapor pressure for equilibration with the salt. This approach was effective at maintaining the ZrCl4 concentration at the solubility limit of 1.3 mol% in the molten salt throughout the duration of two of the chlorination experiments and within about 60% of the solubility limit in the third experiment. Based on the analysis of salt samples, fractional conversion after four hours of reaction for CeO2, and five hours for La2O3, and Nd2O3 were calculated to be 0.97, 0.28, and 0.65 respectively. Assuming a shrinking core diffusion-limited model, the diffusivity of ZrCl4 through the hypothesized ZrO2 layer was calculated for the chlorination of CeO2, La2O3, and Nd2O3 were 1.76 × 10–10 cm2/sec, 7.85 × 10–12 cm2/sec, and 7.42 × 10–12 cm2/sec, respectively. Given the extremely low values calculated for diffusivity, it was concluded that the process is chemical reaction rate limited and that a complete reaction of each rare earth oxide could be achieved. A chemically controlled shrinking core model was shown to also fit the experimental data closely.