Studies on copper(II)- and zinc(II)-mixed ligand complexes of humic acid

Interactions between humic acid (HA), extracted from Brazilian peat soil, and cations of copper(II) and zinc(II) have been examined by infrared spectroscopy, and electrochemical and thermogravimetric analyses. Spectral studies revealed that the interaction with metals occurred mainly at the carboxylic acid groups of HA. The stability constants of HA complexes formed with Cu2+ and Zn2+ were found, by square wave voltammetry and application of the Lingane model, to be 8.93 × 1010 and 2.92 × 102, respectively. Thermal analysis indicated that the stability of HA was increased by the presence of divalent cations of copper and zinc.