Pedosphere 7(3): 257--262, 1997
ISSN 1002-0160/CN 32-1315/P
©1997 Soil Science Society of China
Published by Elsevier B.V. and Science Press
Diffusion of chloride ions in soils: II. Kinetic and thermodynamic characteristics
XU Ming-Gang, Zhang Yi-Ping and LIU Wei-Ning
Department of Soil Science and Agrochemistry, Northwestern Agricultural University, Yangling, Shaanxi 712100 (China)
      The amounts of chloride ions diffused in four soils of different textures at the same water content under different temperature and at varied time were measured by the diffusion cell method using 36Cl-labelled CaCl2 solution. Five kinetic models were used to fit the dynamic process of the diffusion of chloride ions in the soils. It was found that Elovich equation or power function equation was the best model to describe the process. The pseudothermodynamic parameters, i.e. the net reaction energy, the activation entropy, activation enthalpy and activation free energy of the diffusion, were derived from the absolute reaction-rate theory. The results showed that these parameters decreased in the order of loessal soil > black lu soil > lou soil > yellow cinnamon soil, which indicated that the force and the heat-energy barrier to be overcome for diffusion decreased, the diffusion rate increased and the disorder of the soil-solution-ion system due to diffusion decreased successively with the texture becoming heavier in the four soils.
Key Words:  activation enthalpy, activation entropy, chloride ion, diffusion, kinetics
Citation: Xu, M. G., Zhang, Y. P. and Liu, W. N. 1997. Diffusion of chloride ions in soils: II. Kinetic and thermodynamic characteristics. Pedosphere. 7(3): 257-262.
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