Extraction Effect of Ni-Zn By Electrodeposition from Aqueous Acid Solutions

Abstract

The electrodeposition of Zn-Ni is classified by Brenner (1) as anomalous codeposition, because zinc, the less noble metal, is preferentially deposited to nickel the more noble metal. The inhibition of H+ reduction occurs with increasing Zn ions concentration in solution (2). Anomalous codeposition is favored in chloride medium and inhibited in boric acid (3). The reaction kinetic of Zn-Ni codéposition was investigated in acid solutions .The effects of solution composition and pH were analyzed. The inhibition of H+ reduction occurs with increasing Zn ions concentration in solution. Increasing pH values causes Zn deposition during Ni-Zn codeposition. Anomalous codeposition is favored in chloride medium and inhibited in boric acid. When alloy deposition becomes the main process, the interfacial pH is governed by the individual metal deposition that controls the kinetic behavior. The interfacial pH increases during separate Ni deposition, meaning that it occurs with simultaneous consumption of H+. Anomalous codeposition process is not due to a saturation of species at the electrode surface. Results show that it is possible to obtain alloys rich in either nickel or zinc , from an acidic solution,depending on the Ni/Zn concentration ration. For Ni/Zn concentration ratios in the range of 1-5, zinc rich alloys are obtained despite Zn is the less noble metal and even when it is present lower concentrations than nickel. For the highest Ni/Zn concentrations ratio ≥100, the formation of the alloy occurs by a normal deposition, resulting in Ni-rich alloys. Boric acid extends the proton discharge potential to more cathodic values. Thus it can reduce anomalous codeposition since the presence of 0,8M of acid reduces the intensity of the peak corresponding to δ phase that is rich in zinc and enhances the intensity of γ phase containing more nickel than the δ phase.