The effect of different green alkali modification processes on the clinoptilolite surface as adsorbent for ammonium ions; characterization and application

Abstract

Abstract Clinoptilolite natural zeolite was modified by different alkali bearing salts (K, Na, Ca, and Mg) by a green process in the presence of green tea extract as promising green adsorbents for ammonium ions. The modified products displayed significant enhancement in the ion exchange capacities, the surface area, and the morphological properties which was supported by different characterization techniques. The novel modified products achieved stunning adsorption capacities for ammonium ions with experimental qmax of 162 mg/g, 190 mg/g, 230 mg/g and 296 mg/g for K/clinoptilolite, Na/clinoptilolite, Ca/clinoptilolite, and Mg/clinoptilolite, respectively. The theoretical values which were obtained from the equilibrium model are 197.5 mg/g, 219.7 mg/g, 256.2 mg/g, and 340 mg/g for the same products in the order. The adsorption systems of all the prepared adsorbents are highly fitted with both the Pseudo-First order and Pseudo-Second order model with preferences for the first model. Additionally, the uptake of ammonium ions by them is of a monolayer form and of higher fitting with the Langmuir model than the other models considering the correlation coefficient and Chi-squared (χ2) values. The theoretical adsorption energies of K/Clinoptilolite (0.64 kJ/mol), Na/Clinoptilolite (0.76 kJ/mol), Ca/Clinoptilolite (0.9 kJ/mol), and Mg/Clinoptilolite (0.81 kJ/mol) signify physisorption mechanism close to the values of zeolite ion exchange process or coulumbic attractive forces. The modified clinoptilolite products are of high reusability values and applied effectively in the purification of real groundwater and sewage water.