科研之友
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摘要
Radionuclide migration in aquatic environment is influenced by its sorption onto colloids/mineral oxides and the presence of organic complexing anions. With a view to understand the sorption of trivalent actinides by mineral oxides in presence of organic acid, in the present study, Eu(Ⅲ), malonic acid(MA) and γ-alumina are considered as representatives of trivalent actinides, low molecular weight natural occurring organic acid and aluminol sites, respectively. The influence of MA on sorption of Eu(Ⅲ) by γ-alumina was elucidated by batch sorption, spectroscopic techniques and surface complexation modeling, for the first time. Attenuated Total Reflection-Fourier Transform Infrared spectroscopic studies of MA sorbed on γ-alumina revealed the presence of two inner-sphere surface complexes. Batch sorption for binary(alumina-Eu(Ⅲ)) and ternary(alumina-Eu(Ⅲ)-MA) systems were investigated as a function of p H, Eu(Ⅲ) concentration and sequential addition of Eu(Ⅲ)/MA. The p H edge for Eu(Ⅲ) sorption shifts to higher p H with increasing Eu(Ⅲ) concentration. In ternary systems, Eu(Ⅲ) sorption is significantly enhanced at p H < 4.5. Eu(Ⅲ) speciation on γ-alumina is independent of addition sequence of Eu(Ⅲ)/MA. Time resolved fluorescence spectroscopy of Eu(Ⅲ) sorbed on γ-alumina exhibited two surface species, ≡XOEu 2+ and( ≡YO)2 Eu+. The enhancement in I 616/I 592 and lifetime for ternary systems, as compared to binary system, at low p H, indicates the participation of Eu-MA complexes in the formation of surface species in ternary systems. The diffuse layer model has been employed to successfully model the experimental sorption profiles of binary and ternary systems, using code FITEQL 4.0, by considering the surface species identified by spectroscopic techniques.
