The Separation of Americium(III) from Europium(III) by Two New 6,6'-Bistriazinyl-2,2'-Bipyridines in Different Diluents

The synthesis and extraction of americium(III) and europium(III) from aqueous nitric acid solutions by the new BTBP ligands 6,6'-bis(5,5,7,7-tetramethyl-5,7-dihydrofuro[3,4-e]-1,2,4-triazin-3-yl)-2,2'-bipyridine (Cy₅-O-Me₄-BTBP), and 6,6'-bis(5,5,7,7-tetramethyl-5,7-dihydrothieno[3,4-e]-1,2,4-triazin-3-yl)-2,2'-bipyridine (Cy₅-S-Me₄-BTBP) is described. The affinity for Am(III) and the selectivity for Am(III) over Eu(III) of Cy₅-S-Me₄-BTBP were generally higher than for Cy₅-O-Me₄-BTBP. For both ligands, the extraction of Am(III) and Eu(III) from 3 M HNO₃ into 3 mM organic solutions varied with the diluent used. The highest distribution ratios and separation factors observed were in cyclohexanone and 2-methylcyclohexanone, respectively. For Cy₅-S-Me₄-BTBP, there is a strong correlation between the distribution ratio for Am(III) and the permittivity of the diluent used. With 1-octanol as the diluent, low distribution ratios (D(Am) < 1) were observed for Cy₅-S-Me₄-BTBP although this ligand extracts Am(III) selectively (SF_Am/Eu = 16-46 from 1-4 M HNO₃). For Cy₅-S-Me₄-BTBP, Am(III) is extracted as the disolvate. The distribution ratios for Am(III), and the separation factors for Am(III) over Eu(III) are both significantly higher for CyMe₄-BTBP than they are for Cy₅-O-Me₄-BTBP and Cy₅-S-Me₄-BTBP in cyclohexanone. Changing the diluent from cyclohexanone to 2-methylcyclohexanone leads to a decrease in D(Am) but an increase in SF_Am/Eu for Cy₅-S-Me₄-BTBP.