Effect of Mechanical Activation on the Leaching Process of Rare Earth Metal Yttrium in Deep Eutectic Solvents

Abstract

Deep eutectic solvents (DESs) have the potential to be a lixiviant for the selective processing of metal because of their versatile complexation properties. In this study, the leaching behavior of rare-earth carbonate before and after mechanical activation in chloride–urea–malonic acid, the deep eutectic solvents (ChCl-urea-MA DESs) were investigated. Leaching experiments were employed to investigate the effects of reaction temperature and activation time on the leaching efficiency of the metal, yttrium, in DESs. The leaching efficiency of yttrium was determined to be 85.2% when the activation time was 60 min, the leaching temperature was 80 °C and the leaching time was 12 h. The findings showed that mechanical activation increased the yttrium leaching efficiency from 48.61 to 88.37% by lowering the particle size and increasing the contact area of the reaction. The investigation of the yttrium leaching kinetics revealed that, after mechanical grinding, the apparent activation energy of rare-earth carbonate decreased from 83.88 kJ∙mol−1 to 37.4 kJ∙mol−1, and the leaching process of the sample changed from controlled by chemical reaction to controlled by diffusion in the solid product layer. Mechanical activation combined with DESs was proposed as an eco-friendly, sustainable, and effective alternative to conventional mineral acid leaching and solvent, with advantages such as moderate conditions, reusability of the DESs, and no additional wastewater produced. The findings of the study show this method is a good way to recycle rare-earth metals.