Separation of lanthanides by continuous chromatography

Rare earth elements (REE) are widely used in industrial products, such as magnets, superconductors, and batteries. As the worldwide demand of REEs was increasing drastically during the past decade and the applications require very high purity materials, more efficient purification processes are required. Among the purification methods proposed for REE, chromatography has been considered initially, but was then replaced by extraction in the production scale because of its higher cost. In this work, we investigate the possibility of using continuous countercurrent chromatography to decrease the purification cost. In particular, a model mixture of three REE species (praseodymium, cerium, and lanthanum) has been considered with the aim of purifying all three components in a single step to >95% with high yield. It is found that this performance can be achieved with a yield of 75.4% and a productivity increase of 5 to 15-fold with respect to batch chromatography. However, the productivity value remains too low (approximately 1 g per liter stationary phase and day) for large scale applications. This is due to the low loading caused by the limited solubility of the REE in the adopted buffer used. Possibilities to overcome this limitation are discussed.