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

As the associated element of ion-adsorbed type rare earth ores, aluminum ion (Al 3+ ) has a great influence on the purification of gadolinium ion (Gd 3+ ). 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 Al 3+ /Gd 3+ . The extraction capability, separation factor, stripping property and recycling stability of the ionic liquid on the separation of Al 3+ and Gd 3+ were systematically investigated. In addition, the loaded Al 3+ can be totally stripped by 0.08 mol‧L −1 HCl solution. A particularly high separation factor of 923 can be obtained for removing Al 3+ from industrial GdCl 3 feed solution (762 mg‧L −1 Al 3+ and 146 g‧L −1 Gd 3+ ). The removal rate of Al 3+ was up to 98.69% and the recovery rate of Gd 3+ achieved at 92.47% by carboxylic ionic liquid ([N1888][C 7 H 11 O 2 ]) 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 Al 3+ 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 in   industry. This work provides a low-carbon process for efficient removal of Al 3+ from industrial GdCl 3 feed by carboxylic ionic liquids.