Features of Recovery and Precipitation of Lanthanum with Temperature Change

In order to determine the influences of temperature on the recovery and precipitation of Lanthanum, a Pourbaix diagram was constructed using thermodynamic calculations for 283 K, 298 K, 313 K, and 328 K. In terms of the reduction potential of La³⁺, when {La³⁺} is 10⁰, the potential increases from -2.381 V to - 2.369 V as the temperature increases from 283 K to 328 K, but when {La³⁺} is 10^-6, it decreases from - 2.493 V to -2.500 V. The pH of precipitation of La(OH)₃ decreases as the temperature rises. The pH decreases from 7.58 to 6.25 and from 9.58 to 8.25 when {La³⁺} is 10⁰ and 10^-6, respectively. Based on these changes in the potential and pH, it is considered that the pH has a greater effect on the stable area of La³⁺ than dose the reduction potential of La³⁺. Overall, with an increase in temperature, the stable area of La3+ decreases while that of La(OH)₃ increases. When {La³⁺} is 10^-6, as the temperature rises, the stable area of La³⁺ decreases to 95.0%, 90.4%, and 86.3% of the area at 283 K. However, as the temperature decreases, the stable area of La(OH)₃ falls to 92.6%, 84.5%, and 75.7% of the stable area at 328 K. This means that an increase in temperature can reduce the efficiency of the recovery and precipitation process of La³⁺ while increasing the efficiency of the precipitate treatment of La(OH)₃.