The acid-base and complexation properties of humic acids (HAs) extracted from bohemian brown coals were studied. The acid-base behavior corresponds with the model of HA as a mixture of mono- and diprotic acids. This model was also verified on commercial HA substances (Aldrich and Fluka). HA binds strongly with heavy metal ions and the highest stability constant of HA-metal ion complexes was observed for copper(II). Stability constant values were found to decrease in the order: Cu(2+)>Ba(2+)>Pb(2+)>Cd(2+)>Ca(2+). Both acidobasic models for HA alone and those for HA-metal ion interactions were proposed and the computational methodology for polyelectrolyte equilibria studies demonstrated.

Department of Analytical Chemistry Faculty of Science Masaryk University Kotlárská 2 611 37 Brno Czech Republic

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