Studies on effective interaction parameters in extraction of Pr and Nd using Aliquat 336 from NdFeB magnet-leaching solution: Multiple response optimizations by desirability function

Abstract Praseodymium (Pr) and neodymium (Nd) are considered as the light rare earth elements that have received significant attention due to their many applications. The extraction of Pr and Nd from NdFeB magnet-leaching solution using nitrate form of Aliquat 336 was investigated to show the interactive effects in solvent extraction process. The response surface methodology (RSM) based on central composite design (CCD) was used for experimental modeling and optimization. The studied variables included Aliquat 336 concentration of 0.30 to 0.85 mol/L, organic to aqueous phase ratio (O/A) of 1 to 3, pH of 2.0 to 5.0, and nitrate concentration of 2.2 to 5.6 mol/L. According to the results, it was found that there were effective inter-parameter interactions in which justified different feedbacks of the system under different operational conditions. Furthermore, two separated optimizations (i.e., co-extraction efficiency and operational selectivity) were also performed by desirability function method. In the optimization of co-extraction efficiency, the Pr and Nd extraction efficiencies were obtained 99.7% and 93.9%, respectively, while, the above responses in the optimization of operational selectivity were obtained 74.8% and 61.2%, respectively. The values of separation factor were determined same (i.e., 2.1) for both the optimizations. Meanwhile, it was found the stripping of Pr and Nd ions from the loaded organic phase can be effectively conducted under the 0.02 mol/L hydrochloric acid solution within a contact time of 5 min conditions. Also, the FT-IR analysis confirms the transformation of the metal-nitrate complex into the organic phase.