Continuous Mutual Separation of Lanthanides by a Liquid-liquid Countercurrent Centrifugal Extractor with Taylor Vortices

Abstract

Abstract A liquid-liquid countercurrent centrifugal extractor with Taylor vortices which is appropriate for high-performance extraction has been developed. Until now, continuous extraction with more than ten multiple theoretical stages has been demonstrated by a single centrifugal extractor in the case of single specie (zinc extraction with di(2-ethylhexyl)phosphoric acid (D2EHPA)). In the present study, the centrifugal extraction system has been applied to a multispecies case to clarify the separation behavior by countercurrent Taylor mixing. The extraction behaviors of lanthanides (Sm and Eu) with D2EHPA were compared among batch equilibrium measurements, rate measurements by a constant-interfacial-area cell and the continuous experiments by the centrifugal extractor. In the continuous experiment, the separation factor (SF = DEu/DSm) became more than tripled in comparison with the batch equilibrium value due to the multistage extraction effect caused by the countercurrent contact of aqueous/organic phases. The number of theoretical stages of our extractor was evaluated to be 8 to 9 in terms of DEu and 4 to 5 in terms of SF at the rotation speed of 1400 rpm. The SF value from the rate measurement data (SFnoneq; SF in non-equilibrium state) was slightly lower than the batch extraction data (SFeq; SF in equilibrium state) which resulted in difference between theoretical stages evaluated from DEu,eq and SFeq. Although this would slightly decrease the separation efficiency by the continuous extraction, the countercurrent multistage effect was still dominant. By considering this feature, a more effective separation process would be developed by utilizing the countercurrent centrifugal extractor with Taylor vortices.