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Published in Soil Sci Soc Am J 41:1119-1125 (1977)
© 1977 Soil Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
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Proton Binding in Fulvic Acid Extracted From Sewage Sludge-soil Mixtures1

Garrison Sposito, Kenneth M. Holtzclaw and D. A. Keech2

ABSTRACT

Aqueous solutions of two fulvic acids (FA) extracted from sludge-soil mixtures and converted to K-fulvates were titrated potentiometrically at 25°C with HCl in ionic media of 0.1M and 0.2M KCl. Data were obtained for a range of concentrations of FA, although during a titration experiment both FA concentration and ionic strength were rigorously held constant. A simple model was employed to interpret the formation functions calculated using the titration data. This model ascribes the acidic properties of a FA solution to an assembly of hypothetical macromolecules ("mean fulvic acid units") that contain several distinct classes of functional group and are able to associate through hydrogen bonding. Conditional protonation constants were computed for each class of acidic functional group that protonates in the pH range 3–11. The common logarithms of the average protonation constants at 25°C were found to be 3.9, 6.5, and 9.4 for the three classes of weakly acidic functional groups studied. These values were independent (within experimental error) of FA composition and concentration, and of ionic strength in the range investigated.

NOTES

1 Contribution from the Dep. of Soil and Environ. Sci., Univ. of California, Riverside, CA 92521.

2 Associate Professor of Soil Science, Research Associate, and Graduate Research Assistant, respectively.

Received for publication May 9, 1977. Accepted for publication June 24, 1977.






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