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Kinetics of Ammonium Adsorption and Desorption by the Natural Zeolite Clinoptilolite
Author(s) -
Kithome M.,
Paul J. W.,
Lavkulich L. M.,
Bomke A. A.
Publication year - 1998
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1998.03615995006200030011x
Subject(s) - clinoptilolite , adsorption , chemistry , desorption , zeolite , ammonium , kinetics , diffusion , freundlich equation , inorganic chemistry , nuclear chemistry , catalysis , organic chemistry , physics , quantum mechanics , thermodynamics
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 r 2 values ranging from 0.955 to 0.999. With the exception of first‐order kinetics, they also described the desorption process well, with r 2 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.