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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]