On the acid-base properties of humic acid in soil.

Cooke, James D. and Hamilton-Taylor, John and Tipping, Edward (2007) On the acid-base properties of humic acid in soil. Environmental Science and Technology, 41 (2). pp. 465-470. ISSN 0013-936X

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Humic acid was isolated from three contrasting organic-rich soils and acid−base titrations performed over a range of ionic strengths. Results obtained were unlike most humic acid data sets; they showed a greater ionic strength dependency at low pH than at high pH. Forward- and back-titrations with the base and acid revealed hysteresis, particularly at low pH. Previous authors attributed this type of hysteresis to humic acid aggregates—created during the isolation procedure—being redissolved during titration as the pH increased and regarded the results as artificial. However, forward- and back-titrations with organic-rich soils also demonstrated a similar hysteretic behavior. These observations indicate (i) that titrations of humic acid in aggregated form (as opposed to the more usual dissolved form) are more representative of the acid−base properties of humic acid in soil and (ii) that the ionic strength dependency of proton binding in humic acid is related to its degree of aggregation. Thus, the current use of models based on data from dissolved humic substances to predict the acid−base properties of humic acid in soil under environmental conditions may be flawed and could substantially overestimate their acid buffering capacity.

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Journal Article
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Environmental Science and Technology
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16 Dec 2009 15:21
Last Modified:
19 Sep 2023 00:24