Challenges and Innovations of Metal-Based Anode for Greener Hydrometallurgy

Hydrometallurgy is the preferred technology for the industrial recovery and/or production of valuable metals. However, the commercial metal-based anode suffers from dissolution and deactivation in concentrated acidic electrolytes, high current density and abundant impurity ions, raising significant concerns about the hazardous waste emission and energy consumption within hydrometallurgical processes. Recent studies have identified the dissolution-dependent activity and ion migration induced by reactive oxygen species (ROS) as primary mechanisms of the anode deactivation, while also examining the evolutionary mechanisms of ROS and their implications for electrode performance and contaminant transport. Here, this paper presents a thorough review of the recent research and development in the enhancement methods for metal-based anode, including the electrode design (alloying, surface coating, crystalline phase control and heterostructure engineering) and the solute environment control (anions and cations), and explains the mechanisms that underpin these strategies. The treatment and disposal methods of inactivated anode have attracted considerable interest, which can be divided into several categories, recycle, reuse and regeneration. The advantages and disadvantages of anode regeneration are thoroughly evaluated from economic and environmental perspectives. Finally, perspectives are given for the remaining challenges and future research opportunities of the hydrometallurgical metal-based anode in acidic electrolytes.