Ion adsorption mechanisms in oxidic soils; implications for point of zero charge determinations

Stoop, W A (1980) Ion adsorption mechanisms in oxidic soils; implications for point of zero charge determinations. Geoderma, 23 (04). pp. 303-314. ISSN 0016-7061

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In order to clarify the adsorption mechanisms for various ions (e.g., P, K, Ca, Mg), ion adsorption studies were carried out on a range of soils of widely different mineralogical compositions. The soils were classified as: Hydrandept, Gibbsihumox, Eutrustox and Haplustoll and belonged, respectively, to the Honokaa, Halii, Wahiawa and Waialua soil series in Hawaii. Soils containing mostly hydrous Fe and Al oxides, thus colloids of the variable-charge type, retain ions through various types of adsorption mechanisms. As a result, certain interactions between cation adsorption and anion adsorption occur which affect the ion exchange processes and thereby the determination of the point of zero charge (PZC). In this study adsorbed phosphate increased the adsorption of cations and lowered the PZC and adsorbed Ca interfered with PZC determinations unless these were carried out with CaCl2 as supporting electrolyte. It is likely that this latter interference will have influenced the results of many earlier studies because of the very strong adsorption of Ca by oxidic colloids. In this study only part of the adsorbed Ca could be recovered from the two most highly weathered soils, by repeated extractions with NH4-acetate at pH 7. The results indicate that many soils of the tropics can be characterized effectively by their PZC's. One should be aware, however, of the effects of strongly adsorbed ions commonly present in these soils and thus use those supporting electrolytes for the PZC determinations which counteract these effects.

Item Type: Article
Uncontrolled Keywords: Oxidic soils, Soils
Subjects: Others > Soil
Depositing User: Mr Ramesh K
Date Deposited: 13 Sep 2016 08:15
Last Modified: 13 Sep 2016 08:15
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Acknowledgement: The investigations were carried out in the Department of Agronomy and Soils, University of Hawaii, Honolulu, as part of the Ph.D. dissertation of the author. Many thanks are due to the members of the Department of Agronomy and Soils at the University of Hawaii. I am particularly indebted to Dr. Robert L. Fox for providing the assistantship, which made this study possible, but also for his valuable advise and criticism during the course of the various investigations. Furthermore, I would like to acknowledge the encouragement received from Dr. J.A. Mann in dealing with the colloid chemical aspects of this study.
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