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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 15, Number 7
BKCSDE 15(7)
July 20, 1994 

Comparison of the Stability Constants of Cd(Ⅱ)-, Cu(Ⅱ)-, and Pb(Ⅱ)-Humate Complexes
Se Young Choi, Hichung Moon*, Songhui Jun, Kun Ho Chung
A comparative investigation of the complexations of divalent metal ions (Cd, Cu, and Pb) by a well characterized soil humic acid (HA) from Okchun Metamorphic Belt was carried out in 0.05 M KNO3 and pH of 4.5 using ion selective electrodes. A continuous distribution model based on the Scatchard Plot was used to determine the stability constants, because the constants obtained by this modeling technique takes the variations in binding energies into consideration without regards to the manner in which M(Ⅱ) ion is bound on HA. The mean value of log Ki were 4.05±0.60, 4.92±0.36, and 5.63±0.34 l mol-1 for Cd(Ⅱ)-, Pb(Ⅱ), and Cu(Ⅱ)-humate complexes respectively. The values of intrinsic constant (log Kint; binding at strongest site) were 7.12±0.30, 6.59±0.32, and 5.07±0.56 l mol-1 in the order Cu(Ⅱ) > Pb(Ⅱ) > Cd(Ⅱ) ion.
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