Single-Step Recovery of Divalent Mn Component from LiMn<sub>2</sub>O<sub>4</sub> Cathode Material at Hydrothermal Conditions as an Mn–Citrate Complex
Qingxin Zheng, Kensuke Shibazaki, Tetsufumi Ogawa, Masaru Watanabe
Abstract
As one of the most important lithium-ion battery cathode materials for electric vehicles, LiMn2O4 (LMO) cathode material was used as the feedstock of metal recovery in this study. Through a hydrothermal treatment with citric acid (0.3 mol/L), Li and Mn ions were completely leached from a commercial LMO cathode material at 120 °C for 2 min. More importantly, simultaneously with complete leaching of Li and Mn ions from LMO, the Mn component was precipitated and separated as a Mn–citrate complex by adjusting the parameters such as citric acid concentration and holding time. This process avoided the use of high-concentration acids, alkalis, and reductants, and skipped the second separation step, thereby realizing the direct recovery of the Mn component from LMO cathode materials via a green and single-step route. The Mn–citrate complex was identified to be pure C6H8MnO8 or Mn(C6H6O7)H2O, in which Mn existed as in a divalent state. Furthermore, the morphology of the Mn–citrate complex was characterized, and a mechanism was proposed to explain the reactions during this one-step hydrothermal process. Even though the research is just at the initial stage, the Mn–citrate complex reported here is expected to open a new path to the organic acid leaching step of traditional hydrometallurgy and the Mn separation process.