A two-dimensional metal-organic framework for efficient recovery of heavy and light rare earth elements from electronic wastes

Recycling and recovery of rare earth elements (REEs) from electronic wastes can accelerate efforts to mitigate the environmental burden associated with their excessive mining, while catering for their growing demand. Contemporary recovery strategies are yet to make an impact at an industrial scale due to low REE uptakes, complex mechanisms, and high regeneration energies, leading to an overall poor scalability. Here, we report a two-dimensional metal-organic framework (BNMG-1) featuring a dense arrangement of active adsorption sites for the high uptake of heavy and light REEs. BNMG-1 with a lateral dimension of ca. 350 nm and a thickness of 14 nm was synthesized via a facile one-pot reaction using a green solvent under room temperature and atmospheric pressure. The two-dimensional structure of BNMG-1 was resolved using three-dimensional electron diffraction and EXAFS analysis. Batch experiments showed BNMG-1 to have an adsorption capacity of 355.8 mg g(-1) for Nd3+, 323.1 mg g(-1) for Y3+, 331 mg g(-1) for Dy3+, 329mg g(-1) for Tb3+ and 333 mg g(-1) for Eu3+, which is a near-benchmark performance for a non-functionalised MOF. The adsorption efficiency for Nd3+ reached 99 % by 6 h and 88 % by 48 h for Y3+. The adsorption efficiency did not get affected over a pH range of 3 to 6 and retained > 99 % of its adsorption capacity for up to 4 cycles. For application on real-life samples, CFL lamp waste and waste magnets were used as a reservoir of heavy (Yttrium) and light (Neodymium) REEs. BNMG-1 demonstrates an efficient recovery of 57 % for Neodymium from scrap magnets and 27 % for Yttrium from waste fluorescent lamps. This performance, which is maintained under acidic conditions and over multiple cycles, highlights the competitiveness of BNMG-1 for the economic large-scale recovery of REEs.