Ji. Kim et al., AMERICIUM(III)-HUMATE INTERACTION IN NATURAL GROUNDWATER - INFLUENCE OF PURIFICATION ON COMPLEXATION PROPERTIES, Radiochimica Acta, 79(3), 1997, pp. 173-181
The complexation of Am(III) is investigated with humic acid from one o
f the Gorleben groundwaters to describe whether or not the isolation a
nd purification of humic acid influences its complexation behaviour wi
th metal ions. Two different experimental systems are taken for compar
ison, which comprise (i) natural humic acid separated from groundwater
by ultracentrifugation at 6 x 10(5) g and (ii) humic acid purified by
the standard method of acid-base treatment. Am-241 is used for the co
mplexation study in solutions (0.1 M NaClO4) buffered at pH 6.0. Speci
ation is made by UV spectroscopy with the help of peak deconvolution f
or the two absorption bands at 503.2 nm and 505.5 nm for the Am3+ ion
and Am humate complex, respectively. The complexation is found to unde
rgo a charge neutralization reaction of the Am3+ ion with three proton
exchanging sites of humic acid. With respect to the complexation reac
tion, loading capacity and complexation constant, no significant diffe
rence is found for the natural and purified humic acids. An average co
mplexation constant is evaluated to be log beta = 6.26 +/- 0.15. The e
ffect of humic acid purification is also characterized by analysis of
inorganic impurities and TR-spectroscopy. The results lead to the conc
lusion that humate complexation studies made on purified humic acid ar
e directly applicable to natural systems.