The interactions of Mn-54 radionuclide with humic acids (HA) isolated
from the sediment of a tropical estuary at Mahakam were studied in fre
shwater system from the Butoniga impoundment by high voltage paper ele
ctrophoresis. This way, it was possible to detect cationic, anionic an
d immobile Mn-54 species, and to calculate their electrophoretic mobil
ities. In freshwater from the Butoniga impoundment in the pH range fro
m 8.1 to 10.5 on average 69% of Mn-54 is found in the cationic zone, w
hich corresponds to the mobility of Mn(H2O)(6)(2+) ions. The immobile
electrophoretic zone of Mn-54 present in the freshwater at pH>10 in th
e absence of HA probably consists of the sparingly soluble or precipit
ated hydrolytic Mn-54 compounds. These immobile Mn-54 forms are solubi
lized after the addition of HA at elevated pH values. This effect is p
ronounced by the increased concentration of HA and the pH, especially
at HA concentration of 200 mg l(-1) and pH 11.0. The cationic forms of
Mn-54-HA present have lower electrophoretic mobilities [u_=(-1.16+/-0
.05) x 10(-4)cm(2)V(-1)s(-1) at pH 10.5 and u_=(-1.50 +/- 0.27)x 10(-4
) cm(2) V-1 s(-1) at pH 11.0] than the cationic forms of Mn-54 in fres
hwater system without HA added [u_=(-3.09 +/- 0.16)x 10(-4) cm(2) V-1
s(-1) at pH 10.5 and u_=(-2.90 +/- 0.26)x 10(-4) cm(2) V-1 s(-1) at pH
11.0] indicating the formation of new Mn-54 cationic forms after the
interaction with HA. (C) 1998 Elsevier Science Ltd. All rights reserve
d.