The extraction mechanism of astatine-211 in diisopropylether (DIPE) is studied by analyzing the effect of the nature of the aqueous solution and organic solvent on the distribution coefficients characterizing the ratio of organic and aqueous concentration of astatine (D). On the one hand, at a given pH value, D was shown to be independant of the nature and concentration of the counter-ion present in the aqueous solution (Cl-, ClO4-, NO3-). On the other hand, the nature of the organic solvent had a strong effect. D increases as the polarity of the organic solvent increases. These experimental observations are explained by the solvation of astatine by the organic solvent. The back-extraction of astatine from the organic to the aqueous phase is efficient in basic conditions. This is explained by the formation of a hydrolyzed species of astatine presenting no affinity for DIPE. Hydrolysis constants of astatine are deduced from experimental data (logβ1=-3.0±0.1 and logβ2=-14.2±0.1).
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