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Adsorption of soil-derived humic acid by seven clay minerals; a systematic study

Rebecca A. Chotzen, Tamara Polubesova, Benny Chefetz and Yael G. Mishael
Adsorption of soil-derived humic acid by seven clay minerals; a systematic study (in Clays in critical zone, Paul A. Schroeder (editor))
Clays and Clay Minerals (October 2016) 64 (5): 628-638


Humic acid (HA)-clay complexes are well known for their contribution to soil structure and environmental processes. Despite extensive research, the mechanisms governing HA adsorption are yet to be resolved. A systematic study was conducted to characterize the adsorption of a soil-derived HA to seven clay minerals. Clay surfaces affected HA adsorption directly due to structural differences and indirectly by altering solution pH. The following order of HA removal was obtained for the clay minerals at their natural pH: illite >> palygorskite > kaolinite > sepiolite > montmorillonite = hectorite >> talc. Removal of HA (precipitation and adsorption) by kaolinite and illite was attributed to the low pH they induce, resulting in protonation of the clay and HA surfaces. In spite of the low pH, the zeta potential for HA remained negative, which promoted HA adsorption to the protonated clay surfaces by ligand exchange. Ionic strength did not affect HA adsorption to clay minerals with low zeta potentials, indicating that charge screening is not a major mechanism of HA adsorption for these minerals, and supporting the suggestion that ligand exchange is the main adsorption mechanism to pH-dependent sites. The increase in ionic strength did, however, promote HA adsorption to clay minerals with high zeta potentials. At pH 8-9 the order of HA affinity for clay minerals was: palygorskite > sepiolite > montmorillonite = hectorite > kaolinite > illite > talc, emphasizing strong HA interactions with the fibrous clays. This strong affinity was attributed to their large surface areas and to strong interactions with OH groups on these clay surfaces. Results indicated that HA did not enter the intracrystalline channels of the fibrous clays but suggested that their macro-fiber structure facilitates HA adsorption. The sorption of HA to kaolinite further increased in the presence of Cu (super 2+) , and the sorption of Cu (super 2+) increased in the presence of HA, due to a number of synergistic effects. This study emphasizes the diverse effects of clay structure and solution chemistry on HA adsorption.

ISSN: 0009-8604
EISSN: 1552-8367
Serial Title: Clays and Clay Minerals
Serial Volume: 64
Serial Issue: 5
Title: Adsorption of soil-derived humic acid by seven clay minerals; a systematic study
Title: Clays in critical zone
Author(s): Chotzen, Rebecca A.Polubesova, TamaraChefetz, BennyMishael, Yael G.
Author(s): Schroeder, Paul A.editor
Affiliation: Hebrew University of Jerusalem, Department of Soil and Water Sciences, Food and Environment, Rehovot, Israel
Affiliation: University of Georgia, Department of Geology, Athens, GA, United States
Pages: 628-638
Published: 201610
Text Language: English
Publisher: Clay Minerals Society, Chantilly, VA, United States
Meeting name: 2015 EuroClay conference
Meeting location: Edinburgh, GBR, United Kingdom
Meeting date: 20150705July 5-10, 2015
References: 52
Accession Number: 2017-014454
Categories: Geochemistry of rocks, soils, and sedimentsEnvironmental geology
Document Type: Serial Conference document
Bibliographic Level: Analytic
Illustration Description: illus. incl. 2 tables
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, Copyright, Clay Minerals Society. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201710
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