Liquid-liquid Extraction of Lanthanide Ions with bis-2-Ethylhexylphosphinic Acid into Heptane

Bis-2-ethylhexylphosphinic acid(BEHPA) has been studied as a useful extractant for some lanthanide ions(La(III), Ce(III), Pr(III), Nd(III), Sm(III), Eu(III), Gd(III), Tb(III), Dy(III), Y(III), Ho(III), Er(III), Tm(III), Yb(III) and Lu(III)) from their aqueous solutions in the presence of sodium perchlorate. The extraction behavior of the metal ions were investigated and discussed in terms of pH dependency and extractability. The results indicated that the pH of the aqueous phase and BEHPA concentration of the organic solvent were the major parameters that affect the extraction efficiency of the metal ions. The half extraction pH(pH_(1/2)) was found to be 2.85~1.72 for La(III)~Nd(III), 1.75~0.61 for Sm(III)~Y(III) and 1.76~0.73 for Ho(III)~Lu(III) at different concentrations of BEHPA. The metal complexes extracted were proved to be all monomeric species using a slope analysis method. The curve fitting method was also applied to analyze the types of metal complexes extracted: MA_3HA(M means all the fifteen kind lanthanide metal ions). Furthermore, the extraction constants for the extracted metal complexes were estimated.