Simultaneous destruction of Nickel (II)-EDTA with TiO2/Ti film anode and electrodeposition of nickel ions on the cathode

• Decomplexation of Ni-EDTA at anode complied with Ni recovery at cathode.
• Cleavage of amine group at Ni-EDTA leaded to generation of Ni-NTA and Ni-IDA.
• Small molecular acids were indentified.
• Nitrogen-containing products were ammonium and nitrate.
• Liberated nickel was deposited at cathode with zero value.

Ethylenediaminetetraacetic acid (EDTA) forms stable complexes with toxic metals such as nickel. A combined photocatalytic-electrochemical system using TiO2/Ti plate as anode and stainless steel as cathode achieves the simultaneous decomplexation of Ni-EDTA and recovery of nickel. Ni-EDTA was efficiently destroyed in photoelectrocatalytic process in comparison with individual photocatalytic and electro-oxidation process. At 60 min, removal efficiencies of Ni-EDTA were 75%, 12%, and 5%, respectively. At 180 min, the removal efficiency of Ni-EDTA in the photocatalysis and electrolysis processes is only 21% and 18%, respectively. By contrast, nearly 90% Ni-EDTA is removed in the photoelectrocatalytic process. The recovery percentage of nickel was determined to be 45%, 21%, and 5% in the photoelectrocatalysis, electrolysis, and photocatalysis process, respectively. The deposition of nickel ions at the cathode was confirmed by scanning electron microscopy analysis and the nickel species were identified via X-ray photoelectron spectra as nickel with zero value. The removal of Ni-EDTA and recovery of nickel ions increased with the current density and favored at acid conditions. Intermediates detected using a capillary electrophoresis and a high performance liquid chromatography includes Ni-NTA, glycine, maleic acid, glycolic acid, formic acid, acetic acid, oxalic acid, and oxamic acid were identified. The decomplexation pathway of Ni-EDTA was proposed.

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