Efficient degradation and Ni recovery from Ni-EDTA wastewater by Ni/GAC electrodes

Ni-EDTA, a heavy metal complex commonly encountered in electroplating wastewater, is challenging to degrade due to its inherent structural stability. Hence, in this study, we employed a three-dimensional granular electrodes system (3DES) to effectively treat Ni-EDTA and simultaneously recover Ni. Ni/GAC electrode was prepared with granular activated carbon (GAC) as carrier and Ni as catalyst through electrodeposition. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) analysis confirmed that nickel present on Ni/GAC consisted of Ni-0, NiO and Ni(OH)(ads). Results from linear sweep voltammetry (LSV), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) demonstrated an exceptional hydrogen evolution overpotential, reaching 340 mV at 10 mA cm(-2) , with the electrochemical surface area (ECSA) as high as 266.2 cm(2) and charge transfer resistance (Rct) as low as 10.78 Omega. The optimal decomplexation percentages of Ni-EDTA, TCNi, and the recovery of TNi, were determined to be 95 %, 92 %, and 88 %, respectively, under the conditions of 5.00 mA cm(-2) , 3 mM potassium persulfate (KPS), initial pH of 2.76, Ni: EDTA ratio of 1:1. CV indicated that Ni-EDTA can be directly reduced through acquiring two electrons or oxidized on Ni/GAC. In addition, electron spin resonance (ESR) and quenching experiments indicated that the crucial roles played by center dot OH, SO4-center dot and H*. Based on the chemical probe experiments, the relative contributions of direct electron transfer, center dot OH, SO4-center dot and H* were calculated to be 7.6, 34.0, 18.0 and 40.4 %, respectively. In conclusion, the Ni/GAC + KPS system shows a promising strategy to treat Ni-EDTA wastewater.