Enhanced mass transfer process for yttrium separation in novel U-shaped interwoven hollow fiber three-phase membrane modules and numerical simulation

To address the persistent challenges in separating heavy rare earth elements (HREEs) with similar physicochemical properties, this study developed a novel U-shaped interwoven hollow fiber three-phase membrane module (UI-HFTPM) for the selective separation of yttrium ions (Y 3+ ) from Y-rich heavy rare earth solutions. The separation efficiency was systematically explored with respect to membrane structural parameters and operational conditions. Comparative experiments revealed that the UI-HFTPM outperformed parallel hollow fiber three-phase membrane modules (P-HFTPM), achieving a 99.03% purity for Y 3+ in the feed phase after 4 h of operation, while the separation factor ( SF ) between Y 3+ and other HREEs (i.e., SF Ho/Y , SF Er/Y , SF Tm/Y , SF Yb/Y , and SF Lu/Y ) reaching 4.40, 6.09, 6.80, 11.44, and 13.04 within 5 min of operation, respectively. When treating a high-concentration real feed (12.445 g L −1 ), the Y 3+ purity reached 97.20% at 12 h, slightly lower than that obtained under dilute conditions. Additionally, a three-dimensional (3D) computational fluid dynamics (CFD) model was developed to elucidate how secondary flow pattern, induced by the U-shaped structure, enhances radial mixing and thereby influences the mass transfer and reactive extraction/stripping of the representative rare earth ions (Y 3+ and Er 3+ ). This study demonstrates the capability of the CFD model for qualitatively predicting the effects of operational and structural parameters on Y 3+ separation, providing theoretical guidance and technical support for the design, scale-up, and optimization of advanced hollow fiber membrane modules for sustainable rare earth separation.