New insights into the separation of Nd from Pr in hydrochloric and sulfuric acid solutions

Abstract The solvent extraction separation of Nd from Pr with commercially available organic extractants has been studied using statistical design of experiments. In this regard, Taguchi’s L 16 (4 4  × 2 1 ) orthogonal array was used to determine the optimum conditions for maximizing the separation factor between Nd and Pr ( β Nd/Pr ). The effects of controllable operating experimental parameters including initial pH of the aqueous solutions (A: 2–5), concentration of rare earth element (B: 10–40 ppm), extractant type (C: DEHPA, PC88A, TOPO, and Cyanex 572), extractant concentration (D: 10–60 mM), and acid type (E: sulfuric and hydrochloric acid) on the separation performance were studied. Under selected experimental conditions Nd and Pr do not form any major chloride species, whereas both of the elements form cationic and anionic complexes in sulfate solutions (NdSO 4 + , PrSO 4 + , Nd(SO 4 ) 2 − , and Pr(SO 4 ) 2 − ). The optimum operating conditions for maximizing the separation of Nd from Pr occurred at the experimental condition A 4 B 3 C 1 D 3 E 2 , where a maximum separation factor of 2.72 was achieved, which was higher than any values reported in the literature. Analysis of variance (ANOVA) showed that pH, extractant type, and acid type had the most influential effect on the separation of Nd and Pr. DEHPA and hydrochloric acid were found to be the best organic extractant and aqueous solution, respectively. The separation performance of organic extractants followed the order DEHPA > PC88A > Cyanex 572 > TOPO, indicating that the new acidic extractant Cyanex 572 does not perform well for the separation of Nd and Pr.