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. 2019 Jan 22;7(2):2578-2584.
doi: 10.1021/acssuschemeng.8b05604. Epub 2018 Dec 24.

Metal Recovery from Spent Samarium-Cobalt Magnets Using a Trichloride Ionic Liquid

Xiaohua Li  1 , Zheng Li  1 , Martina Orefice  1 , Koen Binnemans  1
Affiliations

Metal Recovery from Spent Samarium-Cobalt Magnets Using a Trichloride Ionic Liquid

Xiaohua Li et al. ACS Sustain Chem Eng. .

Abstract

Recycling of samarium-cobalt (SmCo) magnets is essential due to the limited resources of the mentioned metals and their high economic importance. The ionic liquid (IL) trihexyltetradecylphosphonium trichloride, [P666,14][Cl3], which can safely store chlorine gas in the form of the trichloride anion, was used as an oxidizing solvent for the recovery of metals from spent SmCo magnets. The dissolution was studied considering various mixtures of the ILs [P666,14][Cl3] and [P666,14]Cl, solid-to-liquid ratios and different temperatures. The results showed that the maximum capacity of [P666,14][Cl3] for SmCo magnets was 71 ± 1 mg/g of [P666,14][Cl3], in the presence of an extra source of coordinating chloride ions. The maximum loading of the IL could be reached within 3 h at 50 °C. Four stripping steps effectively removed all metals from the loaded IL, where sodium chloride solution (3 mol L-1), twice water and ammonia solution (3 mol L-1) were used consecutively as the stripping solvents. The regenerated IL showed a similar dissolution performance as fresh IL. Oxidative dissolution of metals in trichloride ILs is easily transferable to the recycling of valuable metals from other end-of-life products such as neodymium-iron-boron magnets and nickel metal hydride batteries.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
Dissolution percentages of samarium powder (< 125 μm) in pure [P666,14][Cl3] with a molar solid-to-liquid ratio of 1:12 as a function of time at room temperature.
Figure 2
Figure 2
Effect of [P666,14][Cl3] concentrations in [P666,14][Cl] on the dissolution efficiency of metals (±10%) with a solid-to-liquid ratio of 20 g/L at room temperature after 24 h. Fe (■), Sm (●), Co (▲), Cu (▼).
Figure 3
Figure 3
Temperature effect on the dissolution rate of Sm in SmCo magnet with IL mixture (50 vol % [P666,14][Cl3] in [P666,14][Cl]) with a solid-to-liquid ratio of 40 g/L at 23 °C (■) and 50 °C (●).
Figure 4
Figure 4
Effect of chloride concentrations in water on the stripping efficiency of metals from synthetic solution IL-Feed-1 with a liquid–liquid phase ratio of 1:1 at room temperature for 1 h. Fe (■), Sm (●), Co (▲), Cu (▼).
Figure 5
Figure 5
Stripping efficiency of metals (±3%) from synthetic solution IL-Feed-1 with a NaCl solution, followed by two stripping steps with pure water with a liquid–liquid phase ratio of 1:1 at room temperature for 1 h.
Figure 6
Figure 6
Concentration of metals (±0.05 mg/g) in the aqueous and IL phases after stripping with aqueous NH3 solutions from synthetic solution IL-Feed-2 with a liquid–liquid phase ratio of 1:1 at room temperature for 1 h.
Figure 7
Figure 7
Conceptual process for recovery of metals from SmCo magnets using a trichloride IL.
See this image and copyright information in PMC

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