Enhanced Separation of Neodymium and Dysprosium by Nonaqueous Solvent Extraction from a Polyethylene Glycol 200 Phase Using the Neutral Extractant Cyanex 923

Abstract

Neodymium and dysprosium can be efficiently separated by solvent extraction, using the neutral extractant Cyanex 923, if the conventional aqueous feed phase is largely replaced by the green polar organic solvent polyethylene glycol 200 (PEG 200). While pure aqueous and pure PEG 200 solutions in the presence of LiCl or HCl were not able to separate the two rare earth elements, high separation factors were observed when extraction was performed from PEG 200 chloride solutions with addition of small amounts of water. This addition of water bridges the gap between traditional hydrometallurgy and novel solvometallurgy and overcomes the challenges faced in both methods. The effect of different variables was investigated: water content, chloride concentration, type of chloride salt, Cyanex 923 concentration, scrubbing agent. A Job plot revealed the extraction stoichiometry is DyCl 3 •4L, where L is Cyanex 923. The McCabe-Thiele diagram for dysprosium extraction showed that complete extraction of this metal can be achieved by a 3-stage counter-current solvent extraction process, leaving neodymium behind in the raffinate. Finally, a conceptual flow sheet for the separation of neodymium and dysprosium including extraction, scrubbing, stripping, and regeneration steps was presented. The nonaqueous solvent extraction process presented in this paper can contribute to efficient recycling of rare earths from end-of-life neodymium-iron-boron (NdFeB) magnets.

Nonaqueous Solvent Extraction for Enhanced Metal Separations: Concept, Systems, and Mechanisms

“…However, with the addition of 30–40 vol % water in PEG 200 (with 1.0 mol L –1 LiCl), efficient extraction of Dy­(III) and good separation of Dy­(III)/Nd­(III) could be concurrently obtained, with a separation factor of up to 69 (Figure ). The extracted complex from the PEG 200 system was found to be [LnCl 3 ·L 4 ] (L represents Cyanex 923), which is the same as the complexes formed in the extraction from the EG system . Based on the fact that the complexes formed in the LP phase are not influenced by MP phase composition, the differences in extraction efficiency can be ascribed, on the one hand, to the different solvation in the MP phase, and on the other hand, to the lower dielectric constants of the polar organic solvents, that increases the stability of inner-sphere chloride complexes.…”

“…Extraction of Nd­(III) and Dy­(III) by Cyanex 923 from a mixture of PEG and water solutions. [Adapted from Dewulf et al]…”

Selective Adsorption of Rare Earth Elements by Zn-BDC MOF/Graphene Oxide Nanocomposites Synthesized via In Situ Interlayer-Confined Strategy

“…Therefore, the separation and purification of REEs have always been a huge challenge in the field of separation science. However, industrial applications have high requirements for the purity of rare earths; in the past few decades, scientific researchers have developed a variety of techniques for achieving the separation of REEs, such as chemical precipitation method, , ion-exchange method, solvent extraction method, − membrane separation method, , and adsorption method. − However, chemical precipitation, solvent extraction, and ion exchange methods have some problems such as long operation cycle, high cost, low separation efficiency, and waste liquid treatment. − As an emerging separation technology, membrane separation has a good separation effect. Although it avoids the use of a large number of organic reagents, the problems of membrane stability and pollution caused by it still need to be resolved. ,− Therefore, in recent years, the adsorption separation of solid phase has become the most commercially valuable separation technology because of its simplicity, low cost, and environmental protection. − …”

Semirigid Ligands Enhance Different Coordination Behavior of Nd and Dy Relevant to Their Separation and Recovery in a Non-aqueous Environment

“…The separation of a single lanthanide (Ln) over another metal of the group represents an actual challenge because of their similar chemical properties. Several methods have been developed to this end, primarily based on fractional precipitation, liquid–liquid extraction, − and ion exchange chromatography, − even if low selectivity and efficiency and the use of a large amount of hazardous and/or costly reagents and solvents often affect the technical, economical, and environmental sustainability of the processes. On the contrary, a relatively easier step involves the separation of the lanthanides from other transition metals.…”