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[Display omitted] • Proposed a novel boron separation and recovery process from spent Nd-Fe-B leaching solution. • Simultaneous removal and recovery of boron to prepare borax pentahydrate. • High boron selectivity with minimal REEs loss in extraction. • Achieved 99.9% and 99.8% efficiencies in two-stage countercurrent extraction and stripping. The accumulation of boron during the recovery of rare earth elements (REEs) from spent Neodymium-Iron-Boron (Nd-Fe-B) magnets affects the extraction of REEs and causes environmental pollution through the boron-containing wastewater. Given that boron is a globally scarce strategic resource, this study proposes a method for the selective separation and recovery of boron from spent Nd-Fe-B magnets leaching solution. The synergistic extraction of boron adopting 2-ethylhexanol (EHA) and 2-ethyl-1,3-hexanediol (EHD), and the extraction mechanism were investigated. Under optimized conditions (30 % EHA-20 % EHD-50 % sulfonated kerosene, 1:1O/A phase ratio, pH 3.3, 10 min), the two-stage countercurrent extraction achieved a remarkable 99.9 % extraction efficiency with minimal loss of REEs. Slope analysis, Raman, FT-IR, and NMR combined with DFT were used to elucidate the extraction mechanism. Specifically, some of the boric acid molecules complexed with the OH groups of EHD to form stable six-membered ring complexes, while another part bound with both EHA and EHD to form linear complexes containing six-membered rings. Employing 0.4 mol/L NaOH as the stripping agent, the two-stage countercurrent stripping process achieved a stripping efficiency of 99.8 %. Subsequently, borax pentahydrate products exceeding 99 % purity were obtained via evaporative crystallization from the stripping solution. Notably, the raffinate contained only ∼ 5 mg/L of boron, which could be further reduced below the discharge standard via the REEs recovery process, allowing for safe emission. This work offers a novel approach for the selective separation and recovery of boron from spent Nd-Fe-B magnets, eliminating its adverse effects on REEs extraction and the environment, while simultaneously recovering a valuable resource. [ABSTRACT FROM AUTHOR]

Motivated by the strategic value of middle-heavy rare earth elements (MHREEs), we proposed a bio-adsorption method to recover ultra-low concentration terbium (Tb(Ⅲ)) from industrial wastewater that originated from the Nd-Fe-B scraps recovery process. It could be found that Tb(Ⅲ) ions as low as 5.34 ng·mL−1(ppb) could be adsorbed onto Ca(Ⅱ)-modified garlic peels (Ca-GP) within 10 min with the adsorption efficiency of 99.2% at pH 3.5. The adsorption behavior of Tb(Ⅲ) onto Ca-GP conformed the Langmuir isotherm model and pseudo-second-order kinetic model. ATR-FTIR, XPS and density-functional theory (DFT) calculations results showed that Tb(Ⅲ) ions could be ion-exchanged with cations in Ca-GP such as Ca(Ⅱ) and -COOH. In application, column experiment results showed that the maximum bed adsorption capacity for Tb, praseodymium (Pr), neodymium (Nd), dysprosium (Dy), and Total rare earth elements (REEs) ions calculated by the Thomas model was 0.06, 3.50, 9.65, 7.34, and 27.37 μg·g−1, respectively, with the initial concentration of 0.37 ng·mL−1 Tb, 20 ng·mL−1 Pr, 44 ng·mL−1 Nd, 67 ng·mL−1 Dy and 170 ng·mL−1 total REEs ions of actual solutions (below the solubility of rare-earth hydroxide). This manuscript thus provided a novel cost-effective and efficient approach to the enrichment and recovery of MHREEs from ultra-low concentration REEs ions-containing solutions. [Display omitted] • Ca(Ⅱ)-modified garlic peels (Ca-GP) biosorbent. • Adsorption of ultra-low concentration of Tb(Ⅲ) (in ppb level) onto Ca-GP. • Ion-exchange of Tb (III) with Ca(Ⅱ) and -COOH of Ca-GP. • Recovery of ppb-level Middle-heavy rare earth from actual solutions. [ABSTRACT FROM AUTHOR]