The NdFeB permanent magnet is a critical
material in digital electronics
and clean energy industry. Traditional recovery processes based on
the solvent extraction technique would consume high energy and large
amounts of chemicals as well as resulting in abundant secondary organic
wastes. In this work, a green process using deep eutectic solvents
(DESs) in the selective leaching technology was designed to recover
NdFeB permanent magnets. Nine kinds of DESs composed of guanidine
were prepared and screened as the leachants. The guanidine hydrochloride–lactic
acid (GUC–LAC) combined DES achieved the highest separation
factor (>1300) between neodymium and iron through simple dissolution
of their corresponding oxide mixture. The mass concentration of Nd
dissolved in the GUC–LAC DES could reach 6.7 × 104 ppm. The viscosity of this type of DES at 50 °C was
36 cP, which was comparable to many common organic solvents. In a
practical recovery of roasted magnet powders, the Nd2O3 product with 99% purity was facilely obtained with only one
dissolution step, followed by a stripping process with oxalic acid.
Even after 3 cycles, the GUC–LAC DES kept the same dissolution
property and chemical stability. With such superior performances in
selective leaching of rare earth elements from transition metals,
the GUC–LAC DES is greatly promising in the rare earth element
recovery field.
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.
The
replacement of traditional solvents in lithium-ion battery
recovery process by deep eutectic solvents (DESs) has been widely
reported. This work proposed a DES modified by reducing agents for
the efficient leaching of LiCoO2 (LCO) and lithium nickel
cobalt manganese oxides (NCMs) to overcome the intractable difficulty
of previous research (high viscosity, poor reuse performance, and
operation conditions). The DES of guanidine hydrochloride (GUC) and
lactic acid (LAC) with 1 wt % ascorbic acid could dissolve almost
100% of LCO and NCMs under a very mild condition at a solid–liquid
ratio of 1:50. The maximum contents in GUC-LAC were 3188 ppm for Li
and 19,045 ppm for Co. After stripping Co by oxalic acid and supplementing
VC, GUC-LAC-VC could maintain the dissolution properties with at least
three cycles. In addition, the acidity and reducibility were measured
through Hammet acidity and cyclic voltammetry methods, as key factors
for the dissolution of Li and Co.
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