Electrochemistry of neodymium in phosphonium ionic liquids: The influence of cation, water content, and mixed anions

Laura Sanchez-Cupido, Jennifer M. Pringle, Amal Siriwardana, Cristina Pozo-Gonzalo*, Maria Forsyth

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

10 Citations (Scopus)

Abstract

Electrodeposition using ionic liquids has emerged as an environmentally friendly approach to recover critical metals, such a neodymium. The investigation of ionic liquid chemistries and compositions is an important part of the move towards efficient neodymium recovery from end-of-life products that needs further research. Thus, in this paper we have investigated a series of phosphonium ionic liquids as potential electrolytic media. Anions such as bis(trifluoromethylsulfonyl)imide (TFSI), dicyanamide (DCA), and triflate (TfO) have been investigated, in combination with short- and long-alkyl-chain phosphonium cations. The work here suggests that [TFSI]- is one of the most promising anions for successful deposition of Nd and that water plays an important role. In contrast, electrochemical behaviour was significantly hindered in the case ofDCAionic liquid, most likely owing to strong coordination between [DCA]- and Nd3+ . Mixtures of anions, [TfO]- and [TFSI]-, have also been investigated in this work, resulting in two reduction processes that could be related to a different deposition mechanism involving two steps, as observed in the case of dysprosium or, alternatively, different coordination environments that have distinct deposition potentials. Additionally, we investigated the influence of electrode substrates - glassy carbon and copper. Cu electrodes resulted in the largest current densities and thus were used for subsequent electrodeposition at constant potential. These findings are valuable for optimising the deposition of Nd in order to develop more efficient and inexpensive recycling technologies for rare earth metals.

Original languageEnglish
Pages (from-to)1080-1087
Number of pages8
JournalAustralian Journal of Chemistry
Volume73
Issue number11
DOIs
Publication statusPublished - Nov 2020

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