Synthesis and characterization of Zn/Ni-Co bilayer coatings using the metals recovered from spent household batteries as raw materials

Abstract

Spent household batteries are a secondary resource that can provide different metals for several industrial processes. This work aims the valorization of these metals using a combination of hydrometallurgical and electrochemical techniques, in order to obtain a bilayer coating of Zn/NiCo over low-carbon steel. The procedure starts with the collection and disassembling of the spent alkaline batteries (65.48 wt % of Zn) and discarded Ni-MH rechargeable batteries (72.49 wt % of Ni and 7.42 wt % of Co) prior to obtaining their electrode materials. These materials were leached in two separated alkaline solutions of NaOH and ammonia (NH4OH) with complexing agents added. Later on, both solutions were used as deposition baths. Once the reduction potential of the metal ions was determined, the coatings were obtained by potentiostatic electrodeposition. The morphology and composition of the coating was studied by scanning electron microscopy (SEM-EDS). Finally, the corrosion resistance of the coating in 3.5 wt % of NaCl solution was evaluated by the following techniques: open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and linear sweep voltammetry (LSV). The results show that the second Ni-Co layer displaces the corrosion potential to more electropositive values and reduces the exchange current density forty times as compared to the Zn layer.