Insights into the effect of cations on cathodic behavior and microstructure in cadmium electrochemical recovery...

Secondary resources provide an essential source for cadmium recovery, but also bring severe environmental problems. Due to the short process and high product purity, electrodeposition is suitable for realizing the reduction, reuse, and recycling of cadmium, while the complex composition of the resources contributes to a complicated electrochemical system. In this work, the effect of common cations (Cu²⁺, Ni²⁺, Fe²⁺, and Zn²⁺) on cadmium electrochemical recovery was investigated from the perspective of electrochemical behavior and microstructure. The results indicated that Cu affected the electrochemical process most prominently, which was deposited on the cathode and formed microcell with Cd, not only impeding the recovery of Cd, but also influencing the purity severely. Comparatively, Ni showed a relatively minor effect, which made the formal potential more negative and alleviated cathodic polarization to some degree. Besides, Fe²⁺ was oxidized by the oxygen released from the anode, and followed by the reaction with Cd, resulting in the redissolution of Cd. With respect to Zn, a low concentration of Zn (≤1 g L^-1) had little influence on electrochemical behavior of Cd, while it was deposited simultaneously with Cd on the cathode at a high concentration (5 g L^-1). Based on the microstructural characterization, the lithops-like cathode cadmium grew up in the presence of Cu, while dendritic Cd was formed affected by Zn, Fe²⁺, and Ni, especially Fe²⁺.