ORIGINAL RESEARCH article
Front. Soil Sci.
Sec. Soil Organic Matter Dynamics and Carbon Sequestration
Volume 5 - 2025 | doi: 10.3389/fsoil.2025.1452870
This article is part of the Research TopicSoil Organic Matter for Global Soil Health and DecarbonizationView all 6 articles
Comparison for Colloidal Stability and Aggregation Behavior of Fluvic and Humic Acids: Effects of Cations and pH
Provisionally accepted
- 1Agrosphere (IBG-3), Institute of Bio- and Geosciences, Julich Research Center, Helmholtz Association of German Research Centres (HZ), Jülich, North Rhine-Westphalia, Germany
- 2Northwest A&F University, Xianyang, China
- 3Henan University of Science and Technology, Luoyang, Henan Province, China
- 4China Agricultural University, Beijing, Beijing Municipality, China
- 5State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Northwest A&F University, Xianyang, Shaanxi Province, China
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Fulvic acid (FA) and humic acid (HA) are organic materials that can form complexes with metal ions, playing a crucial role in predicting the behavior of organic colloids. The colloidal stabilities of FA and HA vary with pH and specific cations, but this has rarely been comprehensively examined. This study systematically compared the aggregation kinetics and colloidal stability of FA and HA and the mechanisms behind their behavior based on particle interaction theory. Results showed that higher pH values stabilized FA and HA colloids by increased electrostatic repulsive energy.Additionally, increased electrolyte concentration destabilized FA and HA colloids by cationic polarization (chemical bond formation). The cations aggregation ability followed Ca 2+ > Mg 2+ > K + > Na + order, showing that the specific ion effects induced by non-classical polarization resulted from the strong electric field of the highly negatively-charged FA and HA. With pH values ranging from 5 to 7 and 9 , FA and HA were stabilized through raising critical coagulation concentrations (CCCs) in NaCl and KCl. With increasing pH, the enhanced electrostatic repulsive energies in Na + and K + systems resulted in weaker aggregation behaviors due to the deprotonation of hydroxyl and carboxyl groups of colloids. Compared with HA, FA had lower Hamaker constant, higher surface negative charges, larger CCCs, and stronger dispersion stability. This work will contribute to the understanding of organic colloidal aggregation mechanisms and act as reference for predicting their environmental behaviors.
Keywords: Critical coagulation concentration, electrostatic repulsive energy, Fourier transformed infrared, Hamaker constant, Specific ion effects
Received: 21 Jun 2024; Accepted: 21 May 2025.
Copyright: © 2025 Wang, Xu, Ma, Li, Hu and Zhao. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence: Chen-yang Xu, Northwest A&F University, Xianyang, China
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