Recovery of rare earth elements from NdFeB magnet by mono- and bifunctional mesoporous silica: Waste recycling strategies and perspectives

Rare earth elements (REEs) such as Nd 3+ and Dy 3+ were recovered from simulated and real leaching solution of the NdFeB magnet via solid phase extraction (SPE). Extraction of REEs from simulated solutions was investigated using silica functionalized with NH 2 -, EDTA and/or phosphonic groups. The effects of several experimental factors (pH, efficiency of adsorbents, selectivity, and elution of metal ions) on extraction of REEs were investigated. Exploiting specific affinities of adsorbents toward REEs in the presence of competing ions, selective separation of REEs was achieved successfully. The affinity of phosphorous/nitrogen containing adsorbents had the descending order of adsorption: Fe 3+ > Dy 3+ > Nd 3+ > Ni 2+ > Al 3+ for multi-component systems. In the first approach, a procedure based on precipitation of Fe 3+ ions combined with SPE was evaluated for the recovery of REEs in two steps. Most of the Fe 3+ ions (85%) were efficiently separated by adding an ammonia solution (pH ~ 2.5). Chemical analysis of precipitate showed, though, a high content of REEs. Extraction of REEs from supernatant liquid via bi-functional mesoporous silica with EDTA and/or phosphonic groups recovered ~97.0% of Nd 3+ with Ni 2+ and Al 3+ ions as impurities. Non-ordered silica functionalized with phosphonic groups, showed economical superiority over other mesoporous adsorbents studied for REEs extraction. Complete recovery (97.8%) of REEs was achieved after several stages of SPE with adsorbents functionalized by P/N-containing groups. The in-advance removal of Fe 3+ ions was a prerequisite for successful implementation of this approach. Finally, separation of Nd 3+ and Dy 3+ was performed from nitric acid media using the gradient elution to obtain 98.4% purity Nd 3+ . The proposed step-by-step SPE procedure by P/N-containing functionalized silica was successfully applied for extraction of REEs (95.5%) in an industrial magnet. This study opens up possibilities for application of the developed approach for the End-of-Life materials recycling. • Recovery of REEs from synthetic and real leach solutions of NdFeB was investigated. • Silicas with phosphonate and aminopolycarboxylate ligands were employed for SPE. • The step-by-step SPE procedure induces to higher extraction (97.8%) of REEs. • Separations of Nd and Dy in mixture were performed by SPE with gradient elution. • Complete recovery (97.1%) of REEs from leach solutions of real NdFeB was achieved.