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Open AccessFeature PaperArticle

Understanding the Recovery of Rare-Earth Elements by Ammonium Salts

1
EaStCHEM School of Chemistry, University of Edinburgh, Edinburgh EH9 3FJ, UK
2
School of Geosciences, University of Edinburgh, Edinburgh EH9 3FE, UK
*
Author to whom correspondence should be addressed.
Metals 2018, 8(6), 465; https://doi.org/10.3390/met8060465
Received: 4 June 2018 / Revised: 14 June 2018 / Accepted: 15 June 2018 / Published: 19 June 2018
(This article belongs to the Special Issue Solvent Extraction of Critical Metals)
While the recovery of rare earth elements (REEs) from aqueous solution by ionic liquids (ILs) has been well documented, the metal compounds that are formed in the organic phase remain poorly characterized. Using spectroscopic, analytical, and computational techniques, we provide detailed chemical analysis of the compounds formed in the organic phase during the solvent extraction of REEs by [(n-octyl)3NMe][NO3] (IL). These experiments show that REE recovery using IL is a rapid process and that IL is highly durable. Karl-Fischer measurements signify that the mode of action is unlikely to be micellar, while ions of the general formula REE(NO3)4(IL)2 are seen by negative ion electrospray ionization mass spectrometry. Additionally, variable temperature 139La nuclear magnetic resonance spectroscopy suggests the presence of multiple, low symmetry nitrato species. Classical molecular dynamics simulations show aggregation of multiple ILs around a microhydrated La3+ cation with four nitrates completing the inner coordination sphere. This increased understanding is now being exploited to develop stronger and more selective, functionalized ILs for REE recovery. View Full-Text
Keywords: ionic liquids; extraction; rare-earths; mass-spectrometry; computational modelling ionic liquids; extraction; rare-earths; mass-spectrometry; computational modelling
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MDPI and ACS Style

Hunter, J.P.; Dolezalova, S.; Ngwenya, B.T.; Morrison, C.A.; Love, J.B. Understanding the Recovery of Rare-Earth Elements by Ammonium Salts. Metals 2018, 8, 465.

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