Approaches to Enhancing Cathodic Nickel Recovery from Ni-EDTA Containing Synthetic Wastewaters

Ethylenediaminetetraacetic acid (EDTA) is widely employed as a chelating agent in the electroless nickel plating industry to form stable metal–organic complexes (e.g., Ni-EDTA). These metal–organic complexes cannot be removed from plating wastewaters by traditional treatments in a cost-effective way. While electrochemical advanced oxidation processes (EAOPs) have been utilized for the efficient degradation of Ni-EDTA at the anode, challenges remain in the simultaneous and effective recovery of nickel at the cathode. In this study, we investigate the efficacy of five cathode materials [i.e., carbon felt (CF), titanium plate, graphite plate (GP), copper plate, and stainless-steel plate] with respect to Ni recovery. The highest Ni removal efficiency of 81.6 ± 0.1% was achieved with the carbon felt cathode which was 30% higher than that of the titanium cathode (52.1 ± 1.4%) with the improvement in performance attributed to the higher rate of mass transport of Ni ions (CF: 4.3 ± 0.4 × 10^–4 s^–1 vs Ti: 1.8 ± 0.2 × 10^–4 s^–1) toward the nanowire structure of carbon felt and to the large surface area of the carbon felt cathode compared with the other cathodes. While the chemical composition of the deposits was independent of the cathodic material or structure, the morphology of deposition varied with the cathode material. The accumulated Ni on the carbon felt surface was successfully recovered either as a nickel salt solution by acid leaching or as high purity NiO by calcinating the Ni-loaded carbon felt cathode at over 800 °C. The performance of the regenerated carbon felt after acid leaching was comparable to that of the fresh cathode even after 10 cycles of use and regeneration via acid leaching with this result confirming the stability and reusability of the carbon felt material.