Characterization and Leaching of Neodymium Magnet Waste and Solvent Extraction of the Rare-Earth Elements Using TODGA

Abstract

The rare-earth elements (REEs) are considered as some of the most critical elements in the EU and the USA today. E-scrap, such as end-of-life neodymium magnets, could be a viable secondary source for the recovery of these elements. Neodymium magnets (NdFeB) consist of considerable amounts of Nd, Dy, Pr, and some other REEs, depending on the specific application. Apart from REEs, neodymium magnets are made up of around 60% iron, which can pose a challenge in their recycling. For example, iron can be dissolved along with other elements during leaching or co-extracted during solvent extraction. In this work, extraction of REEs with TODGA (tetraoctyl-diglycolamide) from a real leachate, obtained by neodymium magnet powder dissolution in nitric acid, was studied. The goal was to selectively extract the REEs from other elements in the solution. TODGA was used as the extracting agent due to its selective extraction properties for REEs and other f-block elements. The influence of the diluent on the overall extraction and the selectivity of the extraction was studied in order to determine application feasibility of future processes. To this end, experiments using Solvent 70 (hydrocarbons C11-C14, B0.5 wt% aromatics), hexane, toluene, cyclohexanone and 1-octanol as the diluents were performed. TODGA has shown good selectivity between REEs and other elements in solution under almost all conditions, reaching the highest distribution ratios of REEs in the aliphatic diluents, while the distribution ratios of other non-REEs reach a mere value of 0.1. An exception was cyclohexanone, which has the ability to extract small amounts of ions itself. The highest separation factors between Dy and the light REEs (Nd and Pr) were observed with a 0.01 M solution of TODGA in Solvent 70. REEs, as group, were extracted with 0.1 M solutions of TODGA in all diluents except for cyclohexanone, which led to extraction of Al and B at amounts greater than 10%. Stripping with over 98% efficiency was achieved using MQ water in one step.

Recovery of rare earths from the green lamp phosphor LaPO4:Ce3+,Tb3+ (LAP) by dissolution in concentrated methanesulphonic acid

“…The leachate was diluted with ultrapure water prior to extraction; several dilution factors were tested (10,30,40,50). Solvent extraction tests were performed with tri-n-butyl phosphate (TBP), bis(2,4,4-trimethylpentyl)phosphinic acid (Cyanex 272) and di-(2-ethylhexyl)phosphoric acid (D2EHPA) as extractants.…”

“…Furthermore, the higher extraction obtained for the heavy REEs compared to those for the light REEs can be explained with the decreasing ionic radii of these elements and the consequent increased charge density. 30 It is well known that D2EHPA is a strong extractant for heavy REEs. 31 In fact, extraction of the elements at the end of the lanthanides series (ytterbium and lutetium) is so strong that it is very difficult to strip these REEs from the loaded organic phase.…”

Extraction of Rare Earth Metal Ions with an Undiluted Hydrophobic Pseudoprotic Ionic Liquid

“…The Nd and nitrate in the ionic liquid (1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide) was reported to form much stronger complexes [21]. From the present result and previous studies [1,5], we developed the following equations based on the ion association mechanism between metal salts and neutral pseudoprotic ionic liquid and the complexation between metal cations (M n+ ) and the carboxylate groups on the pseudoprotic ionic liquid in the presence of salts (NaX).…”

“…Therefore, there is a need to develop a sustainable and economically feasible recycling process for the recovery of rare earth metals from secondary sources to reduce the dependency of the rare earth metal supply on mining production. In secondary sources, neodymium magnets contain a high percentage of rare earth metals (typically 25% Nd) [1]. A small amount of Dy (1%) and Ni (2%) are included to increase temperature stability against demagnetization and to prevent corrosion, respectively.…”

“…Many extractants have been studied for rare earth metal extraction and separation [3]. Even since 2017, many studies have been reported using conventional extractants such as bis(2-ethylhexyl) phosphoric acid [4][5][6], CYANEX 302 (bis (2,4,4-trimethylpentyl) monothiophosphinic acid [7], carboxylic acid [8], N, N, N', N'-tetraoctyl-diglycolamide (TODGA) [1,9] and quaternary ammonium salts (a type of ionic liquid) [10]. Bifunctional ionic liquid extractants composed of a quaternary ammonium cation and a phosphonic acid or carboxylic acid anion were developed for rare earth metal extraction and separation [11].…”