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Chemistry for Sustainable Development

2009 year, number 4

Cadmium Distribution in a Model System Containing Kaolin and Humic Acids

A. A. Kayugin, N. A. Khrytokhin, S. A. Panichev
Keywords: cadmium, kaolin, humic acids, sorption, complexation
Pages: 429-434


Cadmium binding with humic acids (HA) extracted from a sample of a lake bottom sediment is investigated as the dependence on the acidity of the medium in the system (within the pH range 3-10) and on the concentration of cadmium ions (5, 10 and 50 μmol/l). The ion-exchange separation of unbound cadmium ions and its complexes with HA was carried out by means of ion exchange on the sulphocationite followed by analysis by means of the flame atomic absorption spectrometry. Cadmium binding in the system containing kaolin and HA is studied within pH range 3-10. A comparative analysis of the overall cadmium binding in the systems containing kaolin and HA separately and in the system containing them both was carried out for other conditions being the same. The fraction of the metal bound with HA in solution, in precipitate, and on the surface of kaolin was taken into account. It was shown that the additivity of the systems (a decrease in the concentration of the free metal in the ternary system is equal to the sum of the values of concentration decrease in binary systems under the same conditions) is observed within the range pH 4.6-5.8. In other cases, cadmium binding in the ternary system will be lower than in the sum of binary systems: at first, due to HA deactivation due to its adsorption on kaolin surface (in the acid pH region), then due to blocking of the adsorption centres of kaolin (in the neutral and alkaline pH regions).