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

The extraction of Nd3+ and Sm3+, including the extraction and stripping capability as well as the separation effect of Nd3+ or Sm3+, from a sulfuric acid medium, by mixtures of di-(2-ethylhexyl) phosphoric acid (HDEHP, H2A2(0)) and 2-ethylhexyl phosphoric acid mono-2-ethylhexyl ester (HEH/EHP, H2L2(0)) were studied. The distribution ratios and synergistic coefficients of Nd3+ and Sm3+ in different acidities were also determined. A synergistic extractive effect was found when HDEHP and HEH/EHP were used as mixed extractants for Sm3+ or Nd3+. The chemical compositions of the extracted complex were determined as Nd · (HA2)2 · HL2 and Sm · (HA2)2 · HL2. The extraction equilibrium constants, enthalpy change, and entropy change of the extraction reaction were also determined.