EXTRACTION AND SEPARATION FACTORS OF LANTHANIDES AND AMERICIUM IN AQUEOUS NITRIC-ACID DIARYL(DIALKYL)-(DIALKYLCARBAMOYLMETHYL)PHOSPHINE OXIDE SYSTEMS

Extraction of lanthanides (Ln) from aqueous nitric acid with solutions of diphenyl- and dibutyl(diethylcarbamoylmethyl)phosphine oxides (Ph( 2)Et(2) and Bu(2)Et(2), respectively) in dichloroethane is studied as a function of the concentrations of nitric acid and extractant. The di stribution coefficients D decrease with increasing atomic number of Ln . These dependences are characterized by a pronounced tetrad effect fo r Bu(2)Et(2) and by a sharper slope and the absence of the tetrad effe ct for Ph(2)Et(2) Both extractants show low selectivity with respect t o americium separation. The separation factors of Am from individual y ttrium-group lanthanides increase with increasing atomic number of Ln. The separation factors of americium from the total lanthanide group a re about 1.32 for Ph(2)Et(2) and 1.20 for Bu(2)Et(2). The effective ex traction constants of lanthanides (K-2 and K-3) and values of anomalou s aryl strengthening (AAS) are calculated. They decrease with increasi ng atomic number of lanthanide Z. The cause of this trend is discussed in terms of biphilic nature of the aryl group.