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/cm(3)), viscosity (< 30 mPa center dot 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 (beta(Al/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, re-generated and sustained stability over five regeneration cycles. The HDES studied in this paper has the advan-tages of simple preparation, low toxicity, low viscosity, good hydrophobicity and excellent separation effect, which is conducive to the sustainable preparation of high-purity GdCl3.