One-stop decomplexation of Cu-EDTA and Cu capture in rare earth purification wastewater using NdFeB waste/H2O2 system: Performance, mechanism, and application

Conventional advanced oxidation processes (AOPs) face technological bottlenecks in the stepwise treatment of heavy metal–organic complexes (HMCs), and single-step removal strategies have attracted increasing attention. Herein, we pioneered a waste-derived strategy using NdFeB waste (NFBW) to activate H₂O₂ for establishing a heterogeneous Fenton-like system, achieving concurrent Cu-EDTA decomplexation and Cu capture. Remarkably, 99.10 % Cu-EDTA decomplexation and 96.84 % total Cu capture were synchronously achieved within 30 min. This one-step technology is effective over a wide pH range (2.0–9.5). Notably, this system demonstrated practical efficacy in treating rare-earth purification wastewater, achieving synchronous removal of heavy metals (Cu, Zn) and rare-earth elements (Yb, Ce) as mixed organic complexes with effluent meeting industrial discharge standards. Mechanistic investigations revealed that Cu-EDTA decomplexation originated from Fe(Ⅲ)-induced ligand substitution coupled with reactive oxygen species (·OH and ·O₂^-) attack. The ≡Fe(Ⅱ)/≡Fe(Ⅲ)-mediated heterogeneous Fenton reaction synergized with homogeneous Fe(Ⅱ)/Fe(Ⅲ) cycling to generate ROSs, where the B-B bonds and Fe⁰ in NFBW facilitated electron transfer for enhanced redox cycling. Possible pathways for the decomplexation of Cu-EDTA in this system are proposed. The 90.10 % TOC removal verified EDTA mineralization through stepwise degradation pathways. Liberated Cu(Ⅱ) was captured via multiple routes: surface reduction (Cu⁰), precipitation (Cu(OH)₂, Cu₂(OH)₂CO₃), and Fe(OH)₃ adsorption-flocculation. This work not only opens new avenues for Fenton-like treatment of HMC wastewater through a “waste-treats-waste” strategy but also provides new ideas for synergistic activation of H₂O₂ by multivalent iron materials.