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Soil Science Society of America Journal Abstract -

Kinetics of Ammonium Adsorption and Desorption by the Natural Zeolite Clinoptilolite


This article in SSSAJ

  1. Vol. 62 No. 3, p. 622-629
    Received: Feb 4, 1997

    * Corresponding author(s): PaulJ@em.agr.ca
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  1. M. Kithome,
  2. J. W. Paul ,
  3. L. M. Lavkulich and
  4. A. A. Bomke
  1. Agriculture and Agri-Food Canada, Pacific Agri-Food Research Centre, P.O. Box 1000, Agassiz, BC, Canada V0M 1A0
    Dep. of Soil Science, Univ. of British Columbia, Vancouver, BC, Canada V6T 1Z4



The kinetics of NH+4 adsorption and desorption were investigated on the natural zeolite clinoptilolite to ascertain its ability to adsorb and release the important plant nutrient N in its NH+4 form at various pH values and initial NH+4 concentrations. Kinetics of NH+4 adsorption were evaluated on the samples using solutions containing 140.1, 280.2, 560.4, and 840.6 mg L−1 of NH+4-N at pH 4, 5, 6, and 7, equilibrated for 5, 10, 15, 20, 30, 45, 60, 75, 90, and 120 min. Samples for NH+4 desorption were equilibrated with 70.1, 280.2, 560.4, and 1401 mg L−1 NH+4-N solution at pH 4, 5, 6, and 7 for 2.5 h, and adsorbed NH+4 extracted with 2 M KCl for 5, 10, 20, 30, 45, 60, 90, 120, 150, 180, and 300 min. Equilibrium time for NH+4 adsorption ranged from 60 min for 140.1 mg L−1 initial NH+4-N concentration at pH 4 to 120 min for 840.6 mg L−1 initial NH+4-N concentration at pH 7. Desorption was nearly complete in 150 min for low initial NH+4 concentrations and 200 min for high initial NH+4 concentrations. Amounts of NH+4 sorbed increased with increasing pH and initial NH+4 concentrations. Models evaluated included the first-order kinetics, modified Freundlich, parabolic diffusion, Elovich, and heterogeneous diffusion. All the models adequately described the NH+4 adsorption process, with r2 values ranging from 0.955 to 0.999. With the exception of first-order kinetics, they also described the desorption process well, with r2 values ranging from 0.897 to 0.999, for all pH and initial NH+4 concentrations. Reaction rate coefficients (k) were calculated from the modified Freundlich model and ranged from 0.134 to 0.193 min−1 for the adsorption process, and 0.129 to 0.226 min−1 for the desorption process. The models indicated that NH+4 adsorption and desorption by the zeolite was diffusion controlled. Data from this study indicated the potential use of the tested natural zeolite as an NH+4 adsorbent and a controlled-release NH+4 fertilizer.

Pacific Agri-Food Research Centre Contribution no. 562.

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