Sorption of Eu(III) on in the presence of citric acid

Suzuki, Yoshinori; Nankawa, Takuya ; Yoshida, Takahiro*; Ozaki, Takuo; Onuki, Toshihiko; Francis, A. J.*; Tsushima, Satoru*; Enokida, Yoichi*; Yamamoto, Ichiro*

We studied the sorption of Eu(III) on Pseudomonas fluorescens in the absence and presence of citric acid by a batch method. The cells were placed in a solution containing 0.002 mM of Eu(III) and 0, 0.1, or 1 mM of citric acid at pH 3-9 for 5 hours. In the absence of citric acid, almost 100 % of Eu(III) was sorbed on P. fluorescens at pHs below 7; above 7, sorption decreased with an increase in pH. The time course of Eu(III) sorption on P. fluorescens showed that a fraction of it was desorbed into the solution at alkaline pHs, suggesting that the bacterium may release some exudates. With citric acid present, we found that at higher concentrations there was lower sorption of Eu(III), reflecting the formation of Eu(III)-citrate complexes competes with the Eu(III)-cell-surface complexes. This decrease in Eu(III) sorption was significant in alkaline pHs.