| Abstract: | The adsorption of trace metals (Pb, Zn, Cu, Cd and Hg) on calcite, kaolinite and bentonite has been studied in Krka river water of various salinities (S = 3, 20 and 38‰).Model experiments were performed at pH 8 in natural water and in UV-irradiated water samples to determine the importance of natural soluble organic matter. Cold vapour atomic absorption spectrometry was used for the Hg determination, and a differential pulse anodic stripping voltammetry (DPASV) method for determination of other trace metals, using either a hanging mercury drop electrode or a mercury-coated glassy carbon working electrode. The following results have been obtained on calcite: 1. (1) a powerful absorption of Pb and Zn was observed for both natural and UV-irradiated waters at S=20‰; 2. (2) a strong adsorption of Hg was observed in natural water, and significantly lower adsorption in UV-irradiated water at all three salinities, particularly at low salinity; 3. (3) Cd adsorption was of medium intensity in both waters at S=20‰; 4. (4) Cu was practically not adsorbable in both waters at S=20‰ if the total Cu ion concentration was lower than the copper complexing capacity value; 5. (5) Cu adsorption was of a medium intensity at S=38‰. It has not influenced by the EDTA model ligand. Trace metals Pb, Zn and Cu are adsorbable on kaolinite and bentonite at S=38‰, whereas Cd is practically not adsorbed. The Krka River is a calcareous river, which supplies the sea with calcite and aluminosilicates. In the light of our model experiments, we suggest that the self-purification of the Krka River is remarkable in respect to Pb, Zn and Hg; this occurs to a lesser extent for Cu, and is negligible in the case of Cd. |
