GEOC 63 |
| Ping Zhou, Baohua Gu, and Hui Yan. Environmental Science Division, Oak Ridge National Laboratory, P. O. Box 2008, MS 6036, Oak Ridge, TN 37831 |
| Some of metal ions such as Ni can be toxic to microorganisms which are responsible for uranium reduction in groundwater remediation. A potential technique to attenuate the toxicity of metal ions is the introduction of humic substance into contaminated groundwater. By doing this, the solubility and mobility of metal ions can be reduced by binding to humic substance and the activities of microorganisms can be enhanced. However, the complexation of toxic metal ions with humic substance can be decreased with the presence of other metal ions (such as Ca or Al) with high concentrations. A surface complexation model has been applied to model the competitive complexation of Ni, Ca and Al onto humic substance. The humic substance was characterized by two binding sites: a low pH site and a high pH site which were reflections of carboxylic and phenolic functional groups. Potentiometric titrations were used to characterize the intrinsic acidity constants of the two sites and the concentrations of the different surface functional groups. The surface complexation constants of each metal ions were determined. Based on the analysis of surface complexation constants, it was found that the affinities of the three metal ions for the humic substance were in the order of Ni ~ Ca > Al. The presence of Ca and Al could decrease the complexation of Ni complexation. However, Al showed little influence on the complexation of either Ni or Ca with the humic substance when Al concentration was high enough to form precipitation. At low pH value, the complexation of metal ions to the weak binding site was minor. However, at high pH values, the role of weak acid sites in binding metal ions became significant. The complexation of Ni with the humic substance in the contaminated groundwater as functions of both pH and humic substance concentration was developed using the intrinsic surface complexation constants obtained in the experiment. It was found that the presence of high concentration of Ca in the contaminated groundwater can strongly inhibit the complexation of Ni and the increase of both pH and the humic substance concentration can reduce the effect of competitive complexation significantly. |
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Chemistry of Metals in Terrestrial and Aquatic Systems
8:00 AM-11:30 AM, Tuesday, March 30, 2004 Marriott -- Marquis NE, Oral
Division of Geochemistry |