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Issue 17, 2018, Issue in Progress
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Metal coordination in the high-temperature leaching of roasted NdFeB magnets with the ionic liquid betainium bis(trifluoromethylsulfonyl)imide

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Abstract

Ionic liquids are largely used to leach metals from primary (ores) and secondary sources (end-of-life products). However, dry ionic liquids with a carboxylic function on the cation have not yet been used to leach metals at temperature above 100 °C and under atmospheric pressure. The ionic liquid betainium bis(trifluoromethylsulfonyl)imide, [Hbet][Tf2N], was used in the dry state to recover neodymium, dysprosium and cobalt from NdFeB magnets and NdFeB production scrap. The magnets and the scrap were crushed, milled and roasted before being leached above 100 °C. Recovery efficiencies below 10% and a lack of selectivity for all the parameters tested pointed to the importance of water in the dissolution process. The influence of the viscosity of the ionic liquid and the composition of the metal oxides after roasting was investigated as well. Although the dissolution of pure metal oxides was faster than the dissolution of the magnets, the low leaching efficiencies could not be attributed to the composition and crystal structure of the samples, since magnets roasted with the same protocol have already been successfully leached in the past, albeit in the presence of water. The role of water on the mass transfer and on the coordination of the metals was studied by viscometry and by spectroscopic methods, respectively. It is shown that for leaching of rare earths with [Hbet][Tf2N], the presence of ligands such as water is mandatory to saturate the first coordination sphere of the dissolved rare-earth ions. This paper provides new insights in the dissolution mechanism of metal oxides by [Hbet][Tf2N] at leaching temperatures higher than those typically used in hydrometallurgical leaching processes.

Graphical abstract: Metal coordination in the high-temperature leaching of roasted NdFeB magnets with the ionic liquid betainium bis(trifluoromethylsulfonyl)imide

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Publication details

The article was received on 08 Jan 2018, accepted on 28 Feb 2018 and first published on 05 Mar 2018


Article type: Paper
DOI: 10.1039/C8RA00198G
Citation: RSC Adv., 2018,8, 9299-9310
  • Open access: Creative Commons BY-NC license
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    Metal coordination in the high-temperature leaching of roasted NdFeB magnets with the ionic liquid betainium bis(trifluoromethylsulfonyl)imide

    M. Orefice, K. Binnemans and T. Vander Hoogerstraete, RSC Adv., 2018, 8, 9299
    DOI: 10.1039/C8RA00198G

    This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence. Material from this article can be used in other publications provided that the correct acknowledgement is given with the reproduced material and it is not used for commercial purposes.

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