The stability of metal-humate complexes is an important factor determining
and predicting speciation, mobility and bioavailability of heavy metals in
the environment. A comparative investigation of the complexation of Cu(II)
and Pb(II) with humic acid and humic-like ligands, such as benzoic and
salicylic acid, was performed. The analysis was realized at pH 4.0, a
temperature of 25?C and at an ionic strength of 0.01 (NaCl) using the
Schubert ion-exchange method and its modified form. The stability constants
were calculated from the experimental data by the Schubert method for
complexes with benzoic and humic acid. A modified Schubert method was used
for the determination of the stability constants of the complexes with
salicylic acid. It was found that Cu(II) and Pb(II) form mononuclear
complexes with benzoic and humic acid while with salicylic acid both metals
form polynuclear complexes. The results indicate that Pb(II) has a higher
binding ability than Cu(II) to all the investigated ligands. The
Cu(II)-salicylate and Pb(II)-salicylate complexes showed noticeable higher
stability constants compared with their complexes with humic acid, while the
stabilities of the complexes with benzoic acid differed less. Salicylic and
benzoic acids as humic-like ligands can be used for setting the range of
stability constants of humic complexes with Cu(II) and Pb(II).
The Fluoride Complexes of Hafnium(IV). II. Determination of the Stability Constants by the Cation Exchange Method.
