Influence of calcination conditions on deep eutectic solvents (DES) leaching efficiency of light rare earth elements in bastnasite ore

In this century, our daily life is surrounded by technological devices, and Rare Earth Elements (REE) are at the heart of this technological revolution. They are always listed having the highest supply risk in critical minerals published by different countries. From that point of view, their extraction, and creating a secured supply chain is always crucial. In this research, the influence of calcination conditions on REE extraction from bastnasite ore was studied. Identical leaching in Ethylene Glycol (EG)-FeCl₃ media which is one of the Deep Eutectic Solvents (DES) was applied to different calcines to understand calcination parameters on leaching efficiency. After conducting experiments created by Box-Behnken approach with different parameters of temperature, duration, and particles size, the highest Light Rare Earth Elements (LREE) extraction efficiency of 67.22 wt% was achieved at 900° C. However, while conducting control experiments, the highest extraction efficiency was found to be 75.986 wt% as a median of the experiments conducted at 500 °C during 180 min, and with particles finer than 25 µm. This efficiency increase with decreasing temperature is explained by Ce phase transformation from Ce₂O₃ to CeO₂ as proved by XRD analysis. In addition to temperature, particle size was also found highly effective in extraction efficiency especially in Ce extraction. At the experiments conducted at 900 °C, and 270 min but with particles at different size ranges, Ce extraction dramatically dropped from 71.061 wt% to 9.587 wt% at the experiment conducted with finer particles. This lose in efficiency is directly correlated to increasing Ce phase transformation rate due to increasing surface area of fine particles. Non-calcined ore was also leached with DES, and only 10.977 wt% LREE could be extracted. Furthermore, it is concluded that calcination is of vital importance to transform the ore into a soluble form, and temperature, and particle size ranges are found to be two fundamental parameters for tuning the extraction efficiency.