Selective extraction of Nd(III) by novel carboxylic acid based ionic liquids without diluent from waste NdFeB magnets

The development of an environmentally friendly extractant for selective recovery of rare earth elements is critical but still faces significant challenges. Two low viscosity carboxylic acid based ionic liquids [A336][BTA] and [A336][OTA] were synthesized for selective extraction of Nd(III) from waste NdFeB magnets. First, the extraction behaviors of two kinds of ionic liquids were compared under different conditions, such as time, pH value of aqueous phase, dosage of ionic liquids, and concentration of salting-out agent. The optimal extraction condition of [A336][OTA] was optimized by response surface methodology, and the extraction efficiency reached 99.1%. The extraction mechanism was proposed as ion association by UV–Vis spectrum, IR spectrum and 1 H NMR, and was supported from that perspective of quantum chemical calculation. The extraction thermodynamics, kinetics and isothermal model were studied in detail. [A336][OTA] maintained an extraction efficiency of 95.6% even after seven cycles. The extractant shows good selective separation performance in waste NdFeB magnets, and is an extractant with good application prospect. This work has provided an environmentally friendly extractant for the recovery of Nd(III) from waste NdFeB magnets.