Wednesday, 9 November 2005 - 2:30 PM
271-4

Tannate-Induced Structural Perturbation of Aluminum Hydroxides and the Impact on Cadmium Adsorption Kinetics.

G. Yu, U.K. Saha, L.M. Kozak, and P. M. Huang. Dept. of Soil Science, Univ. of Saskatchewan, 51 Campus Drive, Saskatoon, SK S7N5A8, Canada

The impeding effect of organic substances on crystallization of Al precipitation products have been studied for more than three decades; however, impact of the organics-induced structural perturbation and the resultant surface alteration of Al transformation products on their kinetics and mechanisms of adsorption of trace metals still remains to be uncovered. The objective of the present study was to investigate the kinetics of Cd adsorption on the short-range ordered(SRO)Al precipitation products formed under the influence of tannate. The kinetics of Cd adsorption on the SRO Al precipitation products formed at initial tannate/Al molar ratios(MRs)of 0, 0.001, 0.01 and 0.1 was studied at an initial Cd concentration of 0.89 micromole per liter, pH 5.5 and background electrolyte of 0.01 mole NaNO3 per liter at 278, 288, 298 and 313K. The results show that, among the six kinetic models tested, the second-order rate equation best described the kinetic data. The structural perturbation of Al precipitation products by tannate and the resultant development of their microporosity and alteration of surface and charge properties greatly enhanced the rate constants of both the fast and slow reaction processes of Cd adsorption. The heat of activation values for the fast reaction indicate that diffusion is the rate-limiting step in Cd adsorption; by contrast, for the slow reaction, the rate-limiting step is a chemical process. The pre-exponential factor, an index of the frequency of Cd collision with the surface of Al precipitation products, significantly increased with the increase of the initial tannate/Al MR. The role of natural organics, which vary in the structure and functionality, in developing the microporous structure of Al precipitation products and the impact on the dynamics and mechanisms of Cd transformation and transport in natural environments deserves close attention.

Back to Symposium--Humic Substances as Environmental Sorbents: III
Back to S02 Soil Chemistry

Back to The ASA-CSSA-SSSA International Annual Meetings (November 6-10, 2005)