COMPLEXATION STUDY OF HUMIC ACIDS WITH CADMIUM(II) AND LEAD(II)

A set of experiments on the complexation of cadmium and lead with humi c acids were performed at pH 5.0 using normal- and reverse-pulse polar ography and d.c. and differential-pulse anodic stripping voltammetry. The concentration of deprotonated groups at pH 7.0, the average stabil ity parameter, ($) over bar K, the differential equilibrium function, f(K-DEF), and a parameter, Gamma, proportional to the metal buffer cap acity of the system and related to the heterogeneity of the ligand, we re calculated. It was concluded that the complexes are labile within t he experimental error for the time scale of the techniques; that lead complexes are more stable than cadmium complexes and that the ligand h as a more heterogeneous behaviour with respect to lead than to cadmium .