Potentiometric Investigation on Heavy Metal-Humic Acid Interaction : Determination of Formation Constants of Cu(Il), Pb(ll), Zn(II), Co(ll), Ni(II) and Cd(ll) Humic Acid Complexes at pH 4.0

Department of Chemistry, University of North Bengal, Darjeeling-734 430

Manuscript received 7 July 1983, accepted 13 February 2984

Heavy metal-humic acid interactions at different pH and ionic strength have been studied by modified potentiometric technique. Logarithms of overall formation con­stants for different heavy metal complexes at pH 4.0 ranged from 5.98 to 8.80 in 0.05 M KNO₃ and 5.10 to 8.14 in 0.1 M KNO₃ and follow the order Cu(II) > Pb(lI) > Ni(II) > Cd(II) > Co(Il) > Zn(II). At high pH, extra protons are released either through dissociation of hydration water or from very weak acidic functions not titrable within the apparent neutralisation of humic acid. An attempt has been made to interpret the results.