Adsorption Of U(â…¥),Th(â…£) And Eu(â…¢) On γ-Al₂O₃

The adsorption of U(â…¥),Th(â…£) and Eu(â…¢) onγ-alumina was investigated as functions of contact time,pH,ionic strength,solid-to-liquid,sorbate concentrations, ionic strength,phosphate and fulvic acid(FA) by a batch technique.The adsorption of U(â…¥) and phosphate as well as cosorption were quantitatively interpreted in terms of surface complexation model.The experimental results of U(â…¥) and P(â…¤) adsorption indicated that phosphate adsorption onγ-alumina increases with pH from 2.5 to 5.2 and then decreases with pH from 5.2 to 9.4:The adsorption of U(â…¥) onγ-alumina increases with increasing pH over the range of 4～6,from 8%to 97%.The adsorption of phosphate onγ-alumina is insensitive to ionic strength but U(â…¥) sorption increases slightly with decreasing ionic strength.In the co-sorption system,it was found that the presence of phosphate and fulvic acid increases the adsorption of U(â…¥),whereas the presence of U(â…¥) has little effect on the adsorption of phosphate.The effects ofγ-alumina dissolution and CO₂ in the adsorption systems were considered in modeling calculations.Four surface complexes of phosphate,≡XOHAlHPO₄⁺,≡XH₂PO₄,≡XHPO₄^- and≡XPO₄^2- and two surface complexes of U(â…¥),XOUO₂⁺ and≡XOUO₂(OH)₂^-,were respectively used to reproduce the sorption of U(â…¥) and phosphate onγ-alumina.The adsorption of Th(â…£) increases with pH over the range of 3～5 from 7%to 95%and keeps constant at higher pH.The adsorption of Th(â…£) decreases slightly with increasing ionic strength.In the co-sorption system,it was found that the presence of phosphate and fulvic acid significantly increases the adsorption of Th(â…£).With increasing pH over the range of 5～8,the adsorption of Eu(â…¢) onγ-alumina increases from 5%to 98%.The adsorption of Eu(â…¢) onγ-alumina was strongly pH-dependent,which may be interpreted by inner-sphere complexation in absences and presences of CO₂.Three surface complexes≡XOEu²⁺,≡XOEu(OH)⁺ and -XOEu(OH)₃^- were used to interpret the adsorption of Eu(â…¢) onγ-alumina.In the co-sorption system,it was found that the presence of phosphate and fulvic acid significantly increases Eu(â…¢) adsorption.