One-step precipitation and coordination mechanism for highly efficient Fe-Cu separation in acidic solutions

The similar chemical behavior of metal elements in acidic wastewater remains a significant challenge for their deep separation. A key limitation lies in overcoming weak metal selectivity and low separation efficiency. Our study introduced an innovative regulation strategy to enhance the coordination selectivity, enabling the rapid precipitation of Fe^3 + and the efficient complexation of Cu²⁺. Research data clearly revealed surprising separation efficiency of Fe-Cu, two elements with similar hydrolysis and coordination behaviors. Using only reaction temperature of 25°C and alkali concentration of 0.5 mol/L, the Fe content in the solid phase reached 58.65 % and only 0.47 % of Cu content remained by TETA (Triethylenetetramine, C₆H₁₈N₄) regulation. The Fe/Cu ratio was improved from 2.36 before regulation to 124.79, a 53-fold increase. Ultimately, the system achieved complete Fe precipitation, Cu retention rate of 97.4 %, and Fe-Cu separation efficiency of 98.9 %. Importantly, a novel mechanism for rapid one-step precipitation-coordination separation was revealed, emphasizing the role of ligand TETA in lone pairs of electrons in forming a stable tetra-coordinated water-soluble complex via Cu-N bonding. Specifically, the enhanced coordination ability of Cu3d and N2p orbital overlap successfully blocked the interference of Cu on Fe precipitation process. This mechanism enhanced the rapid agglomeration and precipitation efficiency of Fe while suppressing the doping effect of Cu, breaking through the bottleneck of weak metal separation selectivity. This strategy offers a potential new pathway for the green and efficient separation of Fe and Cu in acidic solution systems.