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This article in SSSAJ

  1. Vol. 53 No. 5, p. 1378-1385
     
    Received: Feb 6, 1989
    Published: Sept, 1989


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doi:10.2136/sssaj1989.03615995005300050013x

Mechanisms of Dissolved Organic Carbon Adsorption on Soil

  1. P. M. Jardine ,
  2. J. F. McCarthy and
  3. N. L. Weber
  1. Environmental Sciences Div., Oak Ridge National Lab., P.O. Box 2008, Oak Ridge, TN 37831-6038
    Chemistry Dep., Blackburn College, Carlinville, IL 62626

Abstract

Abstract

The subsurface transport of inorganic and organic contaminants may be strongly related to the movement of dissolved organic carbon (DOC) through a soil profile. A variety of soil chemical and hydrologic factors control the mobility of the DOC, which may enhance or impede the transport of the associated contaminants. In this study, the sources of DOC adsorption on two proposed waste-site soils are defined, and the chemical mechanisms operative during the adsorption process are specified. Adsorption isotherms for the two soils determined at constant pH, ionic strength (I), and temperature indicated that DOC adsorption increased with increasing soil profile depth. Different adsorption capacities were exhibited by the two soils, however, which was related to their contrasting indigenous organic matter contents and mineralogies. The adsorption of DOC by the soils was not a function of solution I (I = 0.001 to 0.1 mol L−1 using NaCl); however, DOC adsorption was dependent on solution pH, with maximum adsorption occurring at ≃4.5. Competitive ion-exchange studies using Na2SO4 as an ionic-strength adjuster suggested that a portion of the DOC was electrostatically bound to the soil via anion exchange. By using thermodynamic principles, the predominant mechanism of DOC retention by the soil was found to be physical adsorption driven by favorable entropy changes. This is supported by preferential adsorption of the hydrophobic organic solutes to the soil relative to the hydrophilic organic solutes.

Joint contribution from Oak Ridge National Lab., Univ. of Tennessee, Knoxville, and Blackburn College. This research was funded by the Subsurface Science Program of the Ecological Research Div., Office of Health and Environmental Research, U.S. Dep. of Energy under contract DE-AC05-84OR21400 with Martin Marietta Energy Systems, Inc. Publication no. 3354.

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