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Published October 1994 | metadata_only
Journal Article

Adsorption of aquatic humic substances on colloidal-size aluminum oxide particles: Influence of solution chemistry


The adsorption of Suwannee River humic substances (HS) on colloidal-size aluminum oxide particles was examined as a function of solution chemistry. The amount of humic acid (HA) or fulvic acid (FA) adsorbed decreased with increasing pH for all solutions of constant ionic strength. In NaCl solutions at fixed pH values, the adsorption of HA and FA increased with increasing ionic strength. The presence of Ca²⁺ enhanced the adsorption of HA but had little effect on FA. For identical solution conditions, the amount (by mass) of HA adsorbed to alumina was always greater than FA. Adsorption densities for both HA and FA showed good agreement with the Langmuir equation, and interpretations of adsorption processes were made from the model parameters. For FA, ligand exchange appears to be the dominant adsorption reaction for the conditions studied here. Ligand exchange is also a major adsorption reaction for HA; however, other reactions contribute to adsorption for some solution compositions. At high pH, cation and water bridging become increasingly important for HA adsorption with increasing amounts of Na⁺ and Ca²⁺, respectively. At low to neutral pH values, increases in these same two cations make hydrophobic bonding more effective. Calculations of HS carboxyl group densities in the adsorbed layer support the proposed adsorption reactions. From the adsorption data it appears that fewer than 3.3 HS-COO⁻ groups per nm² can be bound directly as inner-sphere complexes by the alumina surface. We propose that the influence of aqueous chemistry on HS adsorption reactions, and therefore on the types of HS surface complexes formed, affects the formation and nature of organic coatings on mineral surfaces.

Additional Information

© 1994 Published by Elsevier Ltd. Received 30 November 1992, Accepted 25 July 1994. We gratefully acknowledge Liyuan Liang and Mike Scott for their help in the preliminary stages of this investigation and Elizabeth Carraway for the nonlinear least-squares curve-fitting program used to analyze adsorption data. We would also like to thank Pat Johnsson and two anonymous reviewers for their constructive comments. This work was supported by grants from the Andrew W. Mellon Foundation, William and Flora Hewlett Foundation, Smith and Louise Lee Memorial Endowment, San Francisco Foundation (Switzer Foundation Environmental Fellowship), and the American Water Works Association (Larson Aquatic Research Support Ph.D. Scholarship).

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August 20, 2023
August 20, 2023