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

Abstract

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 (Cy 5 -O-Me 4 -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 (Cy 5 -S-Me 4 -BTBP) is described. The affinity for Am(III) and the selectivity for Am(III) over Eu(III) of Cy 5 -S-Me 4 -BTBP were generally higher than for Cy 5 -O-Me 4 -BTBP. For both ligands, the extraction of Am(III) and Eu(III) from 3 M HNO 3 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 Cy 5 -S-Me 4 -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 Cy 5 -S-Me 4 -BTBP although this ligand extracts Am(III) selectively (SF Am/Eu = 16-46 from 1-4 M HNO 3 ). For Cy 5 -S-Me 4 -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 CyMe 4 -BTBP than they are for Cy 5 -O-Me 4 -BTBP and Cy 5 -S-Me 4 -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 Cy 5 -S-Me 4 -BTBP.

Synthesis and Evaluation of Lipophilic BTBP Ligands for An/Ln Separation in Nuclear Waste Treatment: The Effect of Alkyl Substitution on Extraction Properties and Implications for Ligand Design

“…Equilibrium is reached within 30 minutes for BTBP 12 and within 2 hours for BTBP 13. For BTBP 12, these extraction kinetics are comparable to other BTBP ligands investigated by us Submitted to the European Journal of Organic Chemistry 6 previously, [36] but for the more lipophilic BTBP 13, the extraction kinetics are still significantly slower than those of other BTBP ligands dissolved in cyclohexanone. [35] The relationship between the D values for Am(III) in cyclohexanone and the ligand concentration was then investigated to determine the metal:ligand stoichiometry of the extracted complexes.…”

“…[36] It is possible that a synergistic effect is taking place in the extraction by 12 and 13 in cyclohexanone that does not occur in 1-octanol. We briefly examined the extraction properties of BTBP 12 dissolved in 3-methylcyclohexanone, a diluent we have investigated recently (see Supporting Information), [36] but a detrimental effect on both the extraction ability, and the Am/Eu selectivity was observed in this diluent compared to cyclohexanone. The variation of D Am with phase contact time for both ligands 12 and 13 in cyclohexanone is shown in Figure 10.…”

Influence of diluent alkyl substitution on the extraction of Am(III) and Eu(III) by a 6,6´-bis(1,2,4-triazin-3-yl)-2,2´-bipyridine ligand dissolved in alkylated cyclohexanone diluents

“…The cyclohexanones with more alkyl chains or those with (one or more) longer alkylgroups yielded D values below the detection limits. Thus no significant extraction of either metal ion was observed by the neat diluents themselves, in contrast to cyclohexanone [28]. The extraction of Am(III) and Eu(III) from 4 M HNO 3 by solutions of CyMe 4 -BTBP 1 in the various diluents is shown in Fig.…”

“…The D values for Am(III) were very similar to those found in cyclohexanone but the separation factors were all significantly higher in these diluents. This is due to the small but non-negligible, non-selective extraction of both Am and Eu from 4 M HNO 3 by the neat cyclohexanone diluent itself (D Eu ~ D Am = 0.06) [28]. This property of cyclohexanone is obviously connected to its significant miscibility with nitric acid solutions, particularly at high acidities, as evidenced by changing phase volumes after phase contact.…”

“…2 were each evaluated as potential new diluents for the selective extraction of Am(III) in the presence of Eu(III) from nitric acid solutions by CyMe 4 -BTBP 1. Since cyclohexanone itself extracts to a small degree both Am(III) and Eu(III) in a non-selective manner [28], each diluent was first examined for the background extraction of both metal ions in the absence of CyMe 4 -BTBP 1. When each of the diluents was contacted with 4 M HNO 3 solutions of Am(III) and Eu(III) for 6 h, no changes in the volume of either phase were observed.…”