Voltammetric analysis of the competition between calcium and heavy metals for complexation by humic material

• Published in: Colloids and surfaces. A, Physicochemical and engineering aspects Vol. 95; no. 2; pp. 305 - 313
• Main Authors: van den Hoop, Marc A.G.T., van Leeuwen, Herman P., Pinheiro, JoséPaulo, Mota, Ana M., Simões Gonçalves, Maria de L.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 20.02.1995; Elsevier
• Subjects: Alkaline earth cations; Analytical chemistry; Chemical Sciences; Chemistry; Competition; Earth Sciences; Environmental Sciences; Exact sciences and technology; General and physical chemistry; Geochemistry; Global Changes; Heavy metals; Humic acids; or physical chemistry; Sciences of the Universe; Solution properties; Solutions; Theoretical and; Voltammetry; Competition; Voltammetry; Humic acids; Alkaline earth cations; Heavy metals; Complexation; Calcium complex; Zinc complex; Theoretical study; Transition metal Complexes; Experimental study; Cadmium ion; Alkaline earth metal ion; Heavy metal; Calcium ion; Titration curve; Concentration effect; Cadmium complex; Zinc ion; Humic acid
• ISSN: 0927-7757; 1873-4359
• DOI: 10.1016/0927-7757(94)03037-Z

The competition between calcium and the heavy metals zinc(II) and cadmium(II) in their interaction with humic substances has been studied by differential pulse anodic stripping voltammetry at constant ionic strength. Two experimental methodologies were employed: (1) addition of humic acid to a solution of heavy metal; and (2) addition of heavy metals to a humic acid solution, both using various concentrations of calcium. The former method leads to complexation curves from which an overall mean stability for the heavy metal complex can be obtained. In the latter procedure, mean stability values are obtained at each titration point from the fractions of free and bound heavy metal ions. In the presence of competing ions like calcium, the association of heavy metals with the humic material can be well understood by incorporation of an additional equilibrium reaction for calcium with the humate polyanion. Hence, we are able to obtain information successfully on heavy metal speciation in more complex systems like natural waters, which contain competing cations such as calcium.