Study of the electrochemical behavior of Ni(II) impurity in MgCl2–KCl–NaCl melt

To investigate the separation of Ni(II) impurity and the refining of the electrolyte for magnesium electrolysis, the electrochemical behavior of the Ni(II) impurity in the MgCl2–KCl–NaCl melt at 973 K has been studied using several techniques, including cyclic voltammetry (CV), square wave voltammetry (SWV), and chronoamperometry (CA). Based on the analysis of the CV and SWV curves, it can be inferred that the reduction of Ni(II) in the MgCl2–KCl–NaCl melt at the tungsten electrode exhibits a quasi-reversible reaction. This reaction involves the transfer of a pair of electrons in a single step. The diffusion coefficient was determined at 973 K to be 3.84 × 10−5 cm2 s−1 through the semi-integral method, with the activation energy for diffusion was found to be 45.81 kJ mol−1. The reaction rate constant for the Ni(II) redox reaction was determined to be approximately 10−3 cm s−1 using the Nicholson method. This value suggests that the reaction fall within the quasi-reversible range, as defined by the Matsuda–Ayabe standard. The results obtained from the CA technique have demonstrated that the deposition of nickel on the tungsten electrode occurs through an instantaneous nucleation process, which is primarily controlled by diffusion.