Separation of heavy rare earths by di-(2-ethylhexyl) phosphinic acid: From fundamentals to cascade extraction simulation

Incomplete stripping and high acidity consumption were the major drawbacks for the separation of heavy rare earth elements (HREEs) by the popular extractant 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (P507). This article studied di-(2-ethylhexyl) phosphinic acid (P227) from thermodynamics and kinetics theoretical researches to cascade extraction simulations for the separation of HREEs. P227 was capable of complete stripping for HREEs with low acidity, and had high organic REE loading with clear and fast phase separation. Constant interfacial area cell with laminar flow was implemented to reveal the different kinetics mechanisms for the extraction and stripping of Lu3+. The multi-stages of cascade extraction simulation designed for the separation between Er3+/Tm3+ could be of great significance for practical application. Corresponding products with high purity at both exits obtained successfully via the simulation. All these will provide the promising industrial applications of P227 with more fundamental data and guidance.