Pedosphere 31(5): 736--745, 2021
ISSN 1002-0160/CN 32-1315/P
©2021 Soil Science Society of China
Published by Elsevier B.V. and Science Press
Observation of specific ion effects in humus aggregation process
Rui TIAN, Xinmin LIU, Xiaodan GAO, Rui LI, Hang LI
Chongqing Key Laboratory of Soil Multi-scale Interfacial Process, College of Resources and Environment, Southwest University, Chongqing 400715 (China)
Corresponding Author:Rui TIAN
      Specific ion effects play a vital role in a variety of colloidal and interfacial processes. However, few studies have reported the specific ion effects in the humus aggregation process, which strongly influence the transport and fate of environmental pollutants. In this study, soil humus colloids were prepared and characterized, and the specific ion effects on humus aggregation in electrolyte solutions were investigated at a variety of concentrations and pH values using dynamic light scattering methods. Activation energy (△E), which is known to reflect the dynamics and stability of a colloidal system, was used to quantitatively characterize the specific ion effects. The results showed that given △E value of 2.48×103 J mol-1 at pH 3.0, the electrolyte concentrations were 91.6, 58.2, 3.8, and 0.8 mmol L-1 for Na+, K+, Mg2+, and Ca2+, respectively, thus indicating significant specific ion effects in the humus aggregation process. Most importantly, decreasing the electrolyte concentrations increased the differences in the △E value between two cation species with the same valence (i.e., △ENa - △EK and △EMg - △ECa), while increasing the pH increased the magnitude of △EMg - △ECa. However, the classic Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory and the double layer theory, as well as the currently widely used ionic hydration and dispersion effects, failed to predict the experimentally observed increase in the specific ion effects with decreasing electrolyte concentrations in a quantitative sense. These results have implications for the necessity of involving specific ion effects for a better understanding of humus aggregation and interactions in aqueous and soil systems. Key Words: Derjaguin, Landau, Verwey, and Overbeek theory, double layer theory, ionic dispersion, ionic hydration, supramolecular aggregates
Key Words:  Derjaguin,Landau,Verwey,and Overbeek theory,double layer theory,ionic dispersion,ionic hydration,supramolecular aggregates
Citation: Tian R, Liu X M, Gao X D, Li R, Li H. 2021. Observation of specific ion effects in humus aggregation process. Pedosphere. 31(5): 736–745.
View Full Text

Copyright © 2023 Editorial Committee of PEDOSPHERE. All rights reserved.
Address: P. O. Box 821, 71 East Beijing Road, Nanjing 210008, China    E-mail:
Technical support: Beijing E-Tiller Co.,Ltd.