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

Abstract

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 Dy 2 O 3 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.

Green Leaching of Lithium-Ion Battery Cathodes by Ascorbic Acid Modified Guanidine-Based Deep Eutectic Solvents

“…The δ value of −NH 2 moved to downfield gradually, paralleling to the increase of Co 2+ . This phenomenon matched well with previous work on the separation of rare earths using GUC-LAC . The effect of Co was larger than rare earths because Cl – in GUC donated the electron to the delocalized-π-bond guanidine group by the p−π conjugate, but the formation of [CoCl 4 ] 2– weakened this electron-donating conjugation effect.…”

“…Considering the disadvantages of traditional hydrometallurgy, organic acids, − ionic liquids, , and microorganisms were gradually developed for leaching and recycling of LIBs. Deep eutectic solvents (DESs), as a new type of green solvents, have been reported for dissolution of kinds of metal oxides − since their discovery. Similarly, the active metals in the cathodes of LIBs exist in the form of oxides as well.…”

A Weak Acidic and Strong Coordinated Deep Eutectic Solvent for Recycling of Cathode from Spent Lithium‐Ion Batteries

“…This may be due to the fact that guanidine has a stable structure of delocalized π‐bonds that allows Cl − to be more weakly bound to the cation and more coordinated to Co 3+ . Therefore, Cl − in GHC has a stronger coordination ability than ChCl [22] …”

Effective and selective adsorption of La3+ by a poly-N-isopropylacrylamide phosphoric modified cellulose aerogel

“…Therefore, our country should strengthen the recycling and reutilization of the rare earth metal lanthanum. 12 At present, research on the recovery of rare earth elements mainly uses the extraction precipitation method, 13 solvent extraction method, 14 mesoporous carbon microspheres, 15 and metal organic framework materials. 16 The main disadvantages of these methods are that the experimental methods are complex and diverse, the repetition rate is poor, and although the adsorption effect is good, the practical application prospect is poor.…”