Tailored hydrophobic deep eutectic solvent for removing trace aluminum impurity to produce high-purity GdCl3

In the current industrial production of high-purity gadolinium (Gd) products, aluminum (Al) is enriched into GdCl3 solution as the main impurity element. It is urgent to develop a new process to effectively remove Al3+ from GdCl3 solution. In this paper, a novel strategy for separating Al3+ and Gd3+ based on hydrophobic deep eutectic solvent (HDES) is reported. The main physical properties of HDESs were characterized, including density (<0.90 g/cm3), viscosity (<30 mPa·s), water content (<3.5 %) and water solubility (TOC < 300 mg/L). The extraction performances of HDESs for separating of Al3+ from GdCl3 solution were systemically investigated. Compared with other HDESs, N,N-diethyldodecanamide (DM):ibuprofen (BF) (3:1) HDES has a better separation performance, with the maximum separation factor of Al/Gd (βAl/Gd) being greater than 400. It was found that DM:BF (3:1) HDES could quantitatively remove Al3+ (E% > 99 %) from the original GdCl3 solution (853.9 mg/L Al3+ and 5466.2 mg/L Gd3+) in three continuous counter-current extraction stages. The co-extraction rate of Gd3+ was only 2.43 %, and the purity of GdCl3 in the raffinate was 99.9 %. After the loaded HDES was scrubbed one more time, the comprehensive yield of Gd exceeded 99 %. The loaded HDES could be easily stripped, regenerated and sustained stability over five regeneration cycles. The HDES studied in this paper has the advantages of simple preparation, low toxicity, low viscosity, good hydrophobicity and excellent separation effect, which is conducive to the sustainable preparation of high-purity GdCl3.