Ammonia removal from water using sodium hydroxide modified zeolite mordenite

Natural and modified mordenite zeolites were used to remove ammonium ions from aqueous solution and Koi pond water. The zeolite modification was conducted using sodium hydroxide solutions of different strengths at 75 °C for 24 h. Langmuir, Freundlich, Sips, and Toth equations with their temperature dependent forms were used to represent the adsorption equilibria data. The Langmuir and its temperature dependent forms could represent the data better than the other models. The pseudo-first order model has better performance than the pseudo-second order model in correlating the adsorption kinetic data. The controlling mechanism of the adsorption of NH₄ ⁺ from aqueous solution onto the natural zeolite and the one treated with 6 M sodium hydroxide solution was dominated by physical adsorption. The competition with other ions occurred through different reaction mechanisms so it decreases the removal efficiency of ammonium ions by the zeolites. For the treated zeolite, the removal efficiency decreased from 81% to 66.9%. A Thomas model can represent the experimental data for both adsorption of ammonia from aqueous solution or from Koi pond water.