Highly Selective Electrochemical Magnesium Recovery Using a Spinel-Structured Manganese Oxide

Owing to the rapid growth of the global industry, the importance of securing the supply of resources has increased dramatically. Magnesium is a metallic resource that is in large and steady demands. Current processes for Mg production and refinement require large energy consumption, and additionally, there are environmental issues combined with the mining process. Herein, we report an electrochemical system that selectively recovers Mg²⁺ from mixture solutions, potentially targeting the application to various Mg sources such as brine lake water and wastewater. By using the λ-MnO₂ electrode, whose ion channel size enables selective intercalation of Mg²⁺ among highly populated cations (Na⁺, Mg²⁺, K⁺, and Ca²⁺), Mg²⁺ could be separated from the other ions. The performance of the electrochemical system, which is represented by the selectivity and energetics, was thoroughly investigated. The selectivities toward Mg²⁺ over Na⁺, K⁺, and Ca²⁺ were 27.4, 20.0, and 8.52, respectively, at a concentration level of 20 mM each. Moreover, the flexibility of the system configuration was confirmed by constituting a flow-type process, which is favorable from the viewpoint of industrial applications. The reliability of the system was additionally corroborated by cyclic operations.