Experimental data show that the adsorption of potassium on clinoptilolite after 7-hour relatively fast start eventually becomes diffusion-controlled and slows down. The rate and capacity of adsorption does not depend on the type of solution used – KNO₃ or KCl, but favours higher temperatures. It was found that potassium adsorption is similar to chemisorption and this assumption was confirmed by both equilibrium and kinetic modeling. The applicability of Langmuir and Dubinin–Radushkevich models indicated a non-uniform nature of the clinoptilolite surface and suggested the formation of an adsorbate monolayer, which was used to calculate the clinoptilolite active surface area. The kinetic modeling showed that the pseudosecond order kinetic model was the most suitable for the obtained experimental data, which once more confirmed the chemical nature of potassium adsorption. Despite diffusion-limited potassium adsorption, the release of potassium proceeds at much higher rate in the presence of counter ions and equilibrium can be reached about 10 times faster.

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