COMPLEXATION OF TRIVALENT ACTINIDE IONS (AM3-ACID - THE EFFECT OF IONIC-STRENGTH(, CM3+) WITH HUMIC)

The effect of ionic strength on the complexation of Am3+ and Cm3+ by h umic acid is investigated at pH 6 with three different experimental me thods: ultrafiltration, UV-Visible spectroscopy, and time resolved las er fluorescence spectroscopy (TRLFS). The ionic strength is adjusted b y NaClO4 and varied from 0.001 M to 5.0 M. The metal ion concentration is changed from 9.95 x 10(-9) mol/L Cm3+ to 1.04 X 10(-5) mol/L Am3+, while the humic acid concentration is varied from 5.5 X 10(-8) mol/L to 1.87 x 10(-5) mol/L. This assures a wide range of metal ion to humi c acid concentration ratios to be examined. At pH 6, the loading capac ity (LC) of Gohy-573 humic acid for trivalent actinide ions is found t o change with ionic strength: LC = -(0.126+/-0.012) root I + (0.683+/- 0.014). A relatively small effect of ionic strength on the complexatio n constant can be ascertained. The constant at I=0 evaluated by the SI T model is: Log beta(0) = 6.52 +/- 0.05 and an average value of the co nstants determined over the whole range of ionic strength under invest igation is: log beta(I-m) = 6.24+/-0.14.