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Clean, efficient and economical separation of yttrium (Y) from heavy rare earth elements (HREEs) has always attracted attention. Herein, a strategy for the separation of Y from HREEs based on ternary hydrophobic deep eutectic solvent (HDES) extraction has been first reported. A total of 44 HDESs were prepared with four carboxylic acids as hydrogen bond donors (HBDs), bis(2-ethylhexyl) amine (BEA) as the hydrogen bond acceptor (HBA) and 1-decanol (DL) as the third component. The prepared HDESs have the advantages of simple preparation, no purification requirement, low viscosity, low water solubility and low toxicity. Performances of the HDESs for the separation of Y from HREEs were systematically evaluated. The synergistic effects of each component in the HDESs improve the extraction and separation performances of Y from the HREEs without saponification and organic solvents. Among them, the DL : oleic acid (OA) : BEA-based HDES with OA as the HBD has good extraction ability, higher saturation loading capacity and better phase separation stability. The separation factors of the DL : OA : BEA (9 : 1 : 5) HDES for HREEs (Dy–Lu) and Y in the industrial Y-enriched solution are Dy/Y ≥ 3.05, Ho/Y ≥ 3.37, Er/Y ≥ 4.29, Tm/Y ≥ 6.00, Yb/Y ≥ 10.8, and Lu/Y ≥ 11.2, respectively. The loaded HDES can be easily stripped and remains stable during multiple regeneration cycles. The HDES has shown excellent extraction and separation performance for HREEs (Dy–Lu) and Y, and potential for application in sustainable rare earth separation. [ABSTRACT FROM AUTHOR]

A novel rare earth separation system composed of lauric acid (LA) and primary ammonium (RNH 2) was studied. Compared with individual LA and RNH 2 , the mixed extraction system can significantly improve the extraction and separation ability of rare earth (RE). When LA and RNH 2 are mixed in an equal molar ratio, the synergistic coefficient for extracting Nd(III) in the system reaches 136.85. Effective separation of Nd from Co and Ni can be achieved, with the separation coefficients of 1503 and 2762 for Nd/Co and Nd/Ni, respectively. The ion association mechanism of developed extraction system can avoid the generation of saponification wastewater. Thus, the negative impact of saponification wastewater on the economy and environment can be reduced. The extraction system is simple to be prepared and easy to be stripped, which helps to reduce acid and alkali consumption. Application of this extraction system can effectively realize the separation of RE elements La, Ce, Pr, Nd and transition metals Co, Ni, Mn in nickel-metal hydride (NiMH) battery. This paper provides a new strategy for the development of ionic liquid saponification technology without saponified wastewater. [Display omitted] • LA-RNH 2 extraction system have pronounced synergistic effect on Nd. • The interaction between LA and RNH 2 provides a new strategy for saponification. • This ionic liquid saponification strategy can avoid saponification wastewater. • It has revealed application potential for the recovery of rare earth in NiMH battery. [ABSTRACT FROM AUTHOR]

• LA-RNH 2 extraction system have pronounced synergistic effect on Sm. • This study provides a new idea for the saponification of acidic extractant. • Ion association mechanism of the saponification strategy was investigated. • This ionic liquid saponification strategy can avoid saponification wastewater. • It has revealed application potential for the recovery of SmCo magnets. Acidic extractant is a kind of extractants commonly used in critical metal recovery industry, but the saponification wastewater generated during the saponification process inevitably causes environmental pollution. In order to develop a sustainable separation strategy for rare earth, the synergistic effect between lauric acid (LA) and primary amine N1923 (RNH 2 , with R = C 19 -C 23) was investigated in this paper. The study revealed that the hydrogen bond between LA and RNH 2 was helpful to realize the saponification of LA, thereby significantly improving the extraction and separation performance of LA. Unlike the quaternary ammonium or quaternary phosphonium in ionic liquid saponification studied in the previous study, RNH 2 can independently combine hydrogen ions to achieve the deprotonation of LA without adding alkali or basic resin, which makes the extraction and separation process more environmentally friendly. Aiming at the recovery of samarium cobalt (SmCo) magnet, the separation of Sm and Co in chloride medium was systematically studied. When LA and RNH 2 were combined in equal molar proportions to extract Sm, the extraction system demonstrated a high synergistic coefficient of 61.94, and separation coefficient of Sm and Co was remarkably high at 5326.2. It showed that the LA-RNH 2 extraction system for recovering Sm and Co from actual SmCo magnets could achieve 93.19 % recovery of Co, 90.53 % recovery of Sm and 16,222 Sm/Co separation factor. The LA-RNH 2 extraction system has shown potential applications in Sm/Co separation and waste SmCo magnet recovery processes. It also provides a novel strategy for the saponification of acidic extractant without alkali consumption and saponification wastewater discharge. [ABSTRACT FROM AUTHOR]

In this work, the new hydrophobic deep eutectic solvents (HDESs) based on 2-hexyldecanoic acid (HDA) as a hydrogen bond donor (HBD) were used to selectively enrich trace Th from radioactive waste leach solution. These HDESs are characterized by low toxicity, bio-friendliness, low viscosity and sufficient hydrophobicity. Compared with Al, Mg, Ca and RE, HDESs exhibited exceptional selectivity for Th extraction, along with high loading capacity, easy stripping and stable reusability. The mechanism of Th extraction by the HDES is a cation exchange reaction. Based on the thymol (TL):HDA (1:3) HDES, a short flow closed-loop recovery process of Th in the leach solution of radioactive waste residue was developed. After a single-step extraction, the extraction percentage (E%) of Th exceeded 98.0%, while the E% of other elements was less than 0.14%. After stripping, the concentration of Th in the concentrated solution reached 2.16 × 103 mg/L with a purity of 74.2%, which could be directly used for subsequent purification. By adjusting the pH to 4.00, the raffinate was used as a feed solution for RE elements recovery. The HDES-based extraction strategy for Th is simple, safe, efficient and environmentally friendly, providing a new idea for the recovery of radioactive waste residues. [Display omitted] • HDESs based on 2-hexyldecanoic acid were prepared and characterized. • The separation factor between Th and rare earths is much greater than 1000. • A closed-loop thorium recovery process based on HDES was developed. • The extraction percentage of Th by HDES is more than 98%. [ABSTRACT FROM AUTHOR]

A recyclable IL separation strategy is provided, which simplifies the separation process of Th and RE, reduces chemical consumption, and provides a new idea for the treatment of IATREO waste residue. [Display omitted] • Efficient and sustainable separation of thorium and rare earth achieved using a novel ionic liquid. • The separation factor of Th/REs is as high as 22114. • Functionalization of cations provides more coordination sites to form an ion pair. • Stripping and recycling process of [OB2DTA][CA12] is easier to implement. • REs loss was limited to less than 0.3%, with Th and Fe extraction efficiencies of 99.5% and 100%, respectively. Thorium (Th) containing radioactive waste generated by ion-adsorbed rare earth ore (IATREO) separation plants poses a threat to the environment. The waste residue contains a much higher content of rare earth (RE) than the original IATREO. This study describes novel ionic liquids (ILs) containing cationic functionalization and evaluates their effectiveness in recovering Th and RE from the waste residue leaching solution (WRLS). Di-functionalization of the cation in ILs is more advantageous than mono-functionalization and non-functionalization, providing more coordination sites and achieving higher extraction and separation performance. In the simulated solution at an initial pH of 3, [OB2DTA][CA12] is able to extract 99.0% of Th and only 0.4% of RE, the Th/RE separation factor reaches 22114. The extraction reaction is carried out by an ion association mechanism. After 5 cycles of extraction-stripping-regeneration, the extraction and separation abilities of ILs remain stable. For the HCl leaching solution of waste residue, 99.5% of Th is separated in two extraction stages, while the total loss of RE is only about 15 mg/L. The recyclable separation strategy based on ILs simplifies the separation process of Th and RE, reduces chemical consumption, and provides a new idea for the treatment of IATREO waste residue. [ABSTRACT FROM AUTHOR]