Synergistic extraction of rare earth by mixtures of 2-ethylhexyl phosphoric acid mono-2-ethylhexyl ester and di-(2-ethylhexyl) phosphoric acid from sulfuric acid medium

Abstract The extraction of Nd 3+ and Sm 3+ , including the extraction and stripping capability as well as the separation effect of Nd 3+ or Sm 3+ , from a sulfuric acid medium, by mixtures of di-(2-ethylhexyl) phosphoric acid (HDEHP, H 2 A 2(0) ) and 2-ethylhexyl phosphoric acid mono-2-ethylhexyl ester (HEH/EHP, H 2 L 2(0) ) were studied. The distribution ratios and synergistic coefficients of Nd 3+ and Sm 3+ in different acidities were also determined. A synergistic extractive effect was found when HDEHP and HEH/EHP were used as mixed extractants for Sm 3+ or Nd 3+ . The chemical compositions of the extracted complex were determined as Nd · (HA 2 ) 2 · HL 2 and Sm · (HA 2 ) 2 · HL 2 . The extraction equilibrium constants, enthalpy change, and entropy change of the extraction reaction were also determined.