Selective Dissolution and Separation of Rare Earths Using Guanidine-Based Deep Eutectic Solvents

Producing high-purity rare earth oxides (REOs) would generate large amounts of industrial wastes, and as a consequence, the rare earth industry needs to introduce green separation technology urgently. In this work, four deep eutectic solvents (DESs) as green solvents were employed for the separation and recovery of REOs, and the operation conditions of selective dissolution process were thoroughly investigated. It is found that the DES of guanidine hydrochloride (GUC) and lactic acid (LAC) at a molar ratio of 1:2 held a solubility up to 62000 ppm for La, whereas heavy REOs such as Dy2O3 were almost insoluble in this DES, leading to extremely high separation selectivity between these two types of rare earths. The characterization results showed that the acidity and Cl- coordination of GUC-LAC were the main driving forces for the dissolution of REOs. This separation process based on GUC-LAC has the merits of moderate viscosity, mild operating conditions, and nontoxic and harmless raw materials, which shows a great prospect for application in the field of rare earth green separation.