A novel green synergistic extraction formulation based on D2EHPA for recovering nickel from nickel plating effluent

A new green synergistic extraction agent (di-2-ethylhexyl phosphoric acid (D2EHPA)-decanol) was developed to recycle Ni(II) from nickel plating effluent. The results show that the D2EHPA-decanol mixture carrier provided a significant synergistic effect in the process. When sulfonated kerosene or sunflower seed oil was used as a diluent, the single extraction efficiency of Ni(II) reached 97.8% and 97.1%, respectively. After three-times extraction, the Ni(II) concentration in the nickel plating effluent decreased to below 1 mg/L. Additionally, in the stripping stage, the stripping efficiency of Ni(II) in the D2EHPA-decanol mixed carrier was larger than that of D2EHPA. Mechanism studies indicate that the polar groups (-OH) from decanol initially break the hydrogen bonds in the D2EHPA dimer structure. Afterwards, van der Waals forces shorten the bond length of P-O to form electron-rich centers of O atoms. Finally, a new P-O-Ni structure is formed through interactions between P-O bond and nickel ions under electrostatic forces.