Recovery of samarium(III) and cobalt(II) in synthetic nitric acid solutions using carboxyl functionalized ionic liquids and application to recycling SmCo permanent magnets

Abstract

Samarium (Sm), as one of the lanthanide elements, has a broad application prospect in the synthesis of samarium cobalt permanent magnet materials with high temperature stability, corrosion resistance and oxidation resistance. Due to the unlimited demand of Sm(III), recycling of Sm(III) waste is an effective method to balance economy and supply. In this paper, three novel morpholine carboxylic acid ionic liquids (ILs) were rationally designed and successfully synthesized for the extraction of Sm(III). The effects of alkyl chain length of the ionic liquids, solution acidity, contact time, extractant concentration and temperature were tested in terms of the extraction performances. The results revealed that [(CH2)7COOHmor][NTf2] had the optimal extraction capacity, as well as the extraction efficiency of Sm increased with the increase of pH, reaching >99.9% when the pH was 1.8. In addition, the extraction equilibrium could be achieved within 1 min. Moreover, the slope analysis and FTIR spectral studies proposed a cation exchange extraction mechanism for Sm(III) by [(CH2)7COOHmor][NTf2]. The loaded Sm(III) in organic phase was easy to strip with 0.05 mol/L of HNO3, and the [(CH2)7COOHmor][NTf2] remained stable after 5 cycles. The research of transition metal extraction revealed that Sm(III) could be selectively separated from Ni(II) and Co(II) by adjusting the pH value of the solution. Finally, under the optimized extraction conditions, Sm2O3 with 83.9% yield was obtained by the extraction-stripping-precipitation-calcination process, through the large-scale recovery applications of the simulated waste liquid.