Electrooxidation of nickel-ammonia complexes and simultaneous electrodeposition recovery of nickel from practical nickel-electroplating rinse wastewater

In this experiment, a combined electrooxidation-electrodeposition (EO-ED) system using RuO2/Ti anode and stainless steel cathode was employed to treat nickel-ammonia complexes wastewater, which simultaneously achieved the decomplexation of nickel-ammonia complexes and recovery of nickel metal. Effects of current density, pH value and reaction temperature on electrochemical performance were analyzed. When the current density was 32 mA/cm(2), pH was 9.0 and the temperature was 60 degrees C, the nickel recovery percentage was 99% and the ammonia removal efficiency was 70%. Combined with the SEM-EDX, XRD and XPS analysis for the cathode surface, it was confirmed that the generation of deposition on the cathode surface was zero-valent nickel. Firstly, Nickel-ammonia complexes were destroyed by electrooxidation process, generating Ni2+ ions and free NH3. Then, Ni2+ ions were reduced onto the cathode and free NH3 were further oxidized. Stability of the system for nickel-ammonia complexes treatment was examined by repeated experiments for fifteen successive cycles. The electrochemical system exhibited a satisfactory stability for nickel recovery and ammonia removal, achieving nickel recovery percentage of 85-95% and ammonia removal efficiency of 65-70%, respectively. (C) 2017 Published by Elsevier Ltd