Ternary hydrophobic deep eutectic solvents for the selective extraction of copper from synthetic leaching solution of deep-sea polymetallic nodules: The performance and mechanism

The article introduces a process for the green and efficient recovery of copper from synthetic leaching solution of deep-sea polymetallic nodule (DPN), forming a foundation for the comprehensive utilization of DPN while effectively reducing environmental pollution. A hydrophobic deep eutectic solvent (HDES) was prepared by mixing DL-menthol, decanoic acid, and 1-decanol in a molar ratio of 1:2:3. Under extraction conditions of 50 degrees C, an initial aqueous phase containing 0.1 mol/L sodium acetate (Na(Ac)), pH 5.0, an O/A of 1:4, and an extraction time of 5 min, the extraction efficiency of Cu(II) in a single process reached 90.01 %. Meanwhile, HDES exhibited excellent recyclability, retaining a Cu(II) extraction efficiency of 89.65 % after five cycles. The potential extraction mechanism was investigated using Fourier transform infrared spectroscopy and the slope method, showing that (Ac)- enhanced the extraction kinetics of Cu(II) with HDES. Quantum chemical calculations and optimization results showed that adding 1-decanol improved the stability and reactivity of HDES. This study offers theoretical support for developing environmentally friendly HDES and enhancing green comprehensive utilization technologies for DPN, helping reduce environmental pollution.