Experimental determination and thermodynamic optimization of the LiF-NdF₃ system

Area of Science:

• Materials Science
• Metallurgy
• Physical Chemistry

Background:

• Neodymium production relies on molten salt electrolysis, primarily using LiF-NdF3-Nd2O3 systems.
• The LiF-NdF3 binary phase diagram is critical for optimizing neodymium electrolysis processes.
• Accurate phase diagram data aids in selecting appropriate molten salt compositions and improving production efficiency.

Purpose of the Study:

• To experimentally determine the liquidus and solidus temperatures of the LiF-NdF3 binary system.
• To construct an accurate phase diagram for the LiF-NdF3 system.
• To develop a thermodynamic database for the LiF-NdF3 system using FactSage software.

Main Methods:

• Differential scanning calorimetry (DSC) was employed to measure liquidus and solidus temperatures.
• Thermodynamic optimization using the sub-regular solution model was performed for the binary system.
• FactSage software was utilized to develop a new database for LiF-NdF3.

Main Results:

• The eutectic point was identified at 68.4% LiF-31.6% NdF3 and 731.5 °C.
• Binary interaction coefficients for excess Gibbs free energy were determined: 0L = -39966 + 17.68T, 1L = -7667 + 26.1T, and 2L = -6000.
• Higher liquidus temperatures were observed with industrial-grade NdF3 and NdF3 containing Nd2O3.

Conclusions:

• An accurate LiF-NdF3 phase diagram was constructed, essential for optimizing neodymium electrolysis.
• The thermodynamic database developed will aid in process design and cost reduction.
• The presence of impurities like Nd2O3 significantly impacts the liquidus temperature, requiring careful feedstock selection.