Binding Constants of Lead by Humic and Fulvic Acids Studied
by Anodic Stripping Square Wave Voltammetry¹

Guixiang Quan and Jinlong Yan^z

School of Biological and Chemical Engineering, Yancheng Institute of Technology, Yancheng 224003, China

Received February 04, 2008

Abstract—A better understanding of metal ion binding to soil organic substances is of fundamental importance
in geochemical modeling of environments. Fulvic acids (FA) and humic acids (HA) make up an important part of
soil organic matter, and their binding capacity affects the fate of metal ions and plays an important role in their
mobility. Binding constants of Pb(II) to HA and FA were evaluated by anodic stripping square wave voltammetry
(ASSWV) where the binding reaction was performed at pH 4.5 in a medium of 0.020 mol l^–1 KNO₃. Results
showed that ASSWV technique was well suited for the estimation of the binding capacity of a natural organic mat-
ter towards heavy metals. Based on the voltammetric titration curves, binding constants of Pb(II) complexes
formed with HA and FA were 0.78 10⁶ and 0.15 10⁶ mol^–1 l, which indicated that complex of Pb²⁺ with HA
was more stable than with FA. The average molecular weight of HA and FA prepared from soil samples were also
found to be 1821 g mol^–1 and 805 g mol^–1, respectively.

Key words: voltammetry, humic acid, fulvic acid, complex, stability constant

DOI: 10.1134/S1023193510010118

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