KINETIC-BEHAVIOR OF LANTHANIDE EXTRACTION WITH ACIDIC PHOSPHORUS EXTRACTANTS

The kinetic behavior of lanthanide extraction from HAc-NaAc-EDTA media with three acidic phosphorus extractants(HL), bis(2-ethylhexyl)phosph oric acid (HDEHP), 2-ethylhexylphosphonic acid mono-2-ethylhexyl eater (HEH(EHP)) and bis(2,2,4-trimethylpentyl)phosphinic acid (H(DTMPP)) i n n-octane solution is reported. The observed rate constants, k(o) for the metals (M) lanthanum, neodymium, gadolinium, holmium and lutetium with these three extractants were determined under vigorous mixing. T he rate equation for extraction was determined to be: -d[M]/dt = k'(o) [M][HL](0)(o)[H+](0)[EDTA](-1) = k'(o)[M][EDTA](-1) A mechanism has be en proposed for the extraction reaction under the experimental conditi ons. For a given metal the rate constant as a function of ligand follo wed the order HDEHP > HEH(EHP)> H(DTMPP), the decrease from HDEHP to H (DTMPP) being less than an order of magnitude. It was also found that the rate constants for these metals and yttrium bear an inverse relati onship to the stability constants of their complexes with EDTA.