Selective separation Al3+/Gd3+ by designed carboxylic acid-ionic liquid with low acid and alkali consumption

•Six carboxylic ionic liquids were synthesized to selectively separate Al3+/Gd3+.•High Al3+/Gd3+ separation factor of 923 was achieved by [N1888][C7H11O2] for industrial GdCl3 feed.•High Al3+ removal rate of 98.69% was obtained within one-step extraction.•Loaded [N1888][C7H11O2] can be efficiently regenerated by 0.6 mol‧L−1 HCl solution and 0.5 mol‧L−1 NaOH solution.•The extraction efficiency of Al3+ with regenerated [N1888][C7H11O2] was only reduced by 3% after five cycles. As the associated element of ion-adsorbed type rare earth ores, aluminum ion (Al3+) has a great influence on the purification of gadolinium ion (Gd3+). In this paper, six carboxylic ionic liquids were synthesized with methyltrioctylammonium ([N1888]+) as cation and carboxyl group as anion, and optimized for selective separation of Al3+/Gd3+. The extraction capability, separation factor, stripping property and recycling stability of the ionic liquid on the separation of Al3+ and Gd3+ were systematically investigated. In addition, the loaded Al3+ can be totally stripped by 0.08 mol‧L−1 HCl solution. A particularly high separation factor of 923 can be obtained for removing Al3+ from industrial GdCl3 feed solution (762 mg‧L−1 Al3+ and 146 g‧L−1 Gd3+). The removal rate of Al3+ was up to 98.69% and the recovery rate of Gd3+ achieved at 92.47% by carboxylic ionic liquid ([N1888][C7H11O2]) in one-step extraction. After 0.6 mol‧L−1 HCl solution stripping and 0.5 mol‧L−1 NaOH solution regenerating, the extraction efficiency of Al3+ was only reduced by 3% after 5 cycles of organic phase. With the low acid and base concentration, it greatly reduced the chemical consumption and significantly the emission of high ammonia–nitrogen wastewater inindustry. This work provides a low-carbon process for efficient removal of Al3+ from industrial GdCl3 feed by carboxylic ionic liquids.