Voltammetrische metaalspeciatie in oppervlaktewater: kinetiek en adsorptie
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Series / Report no.
Open Access
Type
Report
Language
nl
Date
1997-01-31
Research Projects
Organizational Units
Journal Issue
Title
Voltammetrische metaalspeciatie in oppervlaktewater:
kinetiek en adsorptie
Translated Title
Voltammetric metal speciation in surface water:
kinetics and adsorption
Published in
Abstract
In het kader van onderzoek naar de verdeling van vrije
en gebonden metalen in natuurlijke systemen is de labiliteit van een aantal
verschillende zwaar-metaal/ligand systemen bestudeerd onder stripping
voltammetrische condities. De onderzochte systemen bestaan uit de zware
metalen Cd, Cu en Pb op verschillende concentratieniveaus en een drietal
oppervlaktewatermonsters, die onderling verschillen in pH,
complexeringscapaciteit, DOC-gehalte, zoutniveau en concentraties
competitieve kationen. Op basis van de gevonden relatie tussen
voltammetrische stroom en potentiaal versus de tijdschaal van het
experiment, in dit geval de roersnelheid, is kwalitatieve informatie
verkregen over de labiliteit van de verschillende metaal/complexen. De
Cd/complexen waren voor alle drie de monsters het meest labiel, terwijl de
labiliteit van de Pb en Cu/complexen sterk afhankelijk was van het type
monster. Voor labiele en statische metaalcomplexen is theorie beschikbaar
om vanuit de voltammetrische respons de speciatie te berekenen. Ter
illustratie is op basis hiervan voor een van de Cd/complexen een K-waarde
geschat van 1900 l/mol exp-1. Middels variatie in depositietijd is
mogelijke adsorptie van liganden aan het kwikelectrode-oppervlak onderzocht.
Voor de zes onderzochte metaal/oppervlaktewatermonsters is geen
noemenswaardige adsorptie geconstateerd, waardoor de interpretatie van het
voltammetrisch signaal relatief eenvoudig blijft.
Within the framework of metal speciation and bioavailability research, the kinetics of the association and dissociation reactions of heavy metals with various complexes in natural systems play an important role in understanding the chemical properties of these systems. In this respect, the lability of various natural heavy metal/complexes was studied under stripping voltammetric conditions. Three surface water samples were selected varying in pH, complexation capacity, salt concentration and concentrations of competitive cations. On the basis of the obtained relationship between voltammetric response and time scale of the experiment (in this case the rotation frequency of the stirrer) qualitative information was obtained with respect to the lability of Cd, Cu and Pb/complexes. The Cd/complexes were found to be most labile in all cases. The lability of the Cu and Pb/complexes was highly dependent on the type of surface water. For labile and static metal complexes, theory is available for calculating the actual speciation on the basis of the voltammetric response. Following this procedure, for the labile Cd/complexes a K-value of 1900 l/mol exp.-1 was estimated. In addition, by varying the deposition time information was obtained with respect to possible adsorption of the natural ligands on the surface of the mercury electrode. For the present set of samples, the adsorption was found to be absent or negligible and, hence, the interpretation of the voltammetric reponse remains quite simple.
Within the framework of metal speciation and bioavailability research, the kinetics of the association and dissociation reactions of heavy metals with various complexes in natural systems play an important role in understanding the chemical properties of these systems. In this respect, the lability of various natural heavy metal/complexes was studied under stripping voltammetric conditions. Three surface water samples were selected varying in pH, complexation capacity, salt concentration and concentrations of competitive cations. On the basis of the obtained relationship between voltammetric response and time scale of the experiment (in this case the rotation frequency of the stirrer) qualitative information was obtained with respect to the lability of Cd, Cu and Pb/complexes. The Cd/complexes were found to be most labile in all cases. The lability of the Cu and Pb/complexes was highly dependent on the type of surface water. For labile and static metal complexes, theory is available for calculating the actual speciation on the basis of the voltammetric response. Following this procedure, for the labile Cd/complexes a K-value of 1900 l/mol exp.-1 was estimated. In addition, by varying the deposition time information was obtained with respect to possible adsorption of the natural ligands on the surface of the mercury electrode. For the present set of samples, the adsorption was found to be absent or negligible and, hence, the interpretation of the voltammetric reponse remains quite simple.
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