SOLVENT-EXTRACTION OF RARE-EARTH-METALS WITH BIS(2-ETHYLHEXYL)PHOSPHINIC ACID

The extraction behavior of tervalent rare-earth metals (Ln) using a he ptane solution containing bis(2-ethylhexyl)phosphinic acid (PIA-8, HR) from 0.1 mol/dm(3) sodium perchlorate media was studied. The pH(0.5) values and separation factors obtained were compared among the metals. The stoichiometry of the extracted species and the extraction constan ts for the present aqueous/heptane system were determined by slope ana lysis. It is demonstrated that the rare-earth metals were extracted as monomers LnR(3).mHR (m = 3, 4, 5 or 6), and the extracted species cou ld be stripped into a relatively low concentrated hydrochloric acid. P IA-8 was found to be the most selective extractant for the mutual sepa ration of rare-earth metals among the other phosphinic acids reported.