THE INTERACTIONS OF MN-54 WITH HUMIC ACIDS IN FRESH-WATER SYSTEMS

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.