An Equilibrium Ion‐Exchange Study on the Removal of NH₄⁺ Ion from Aqueous Effluent Using Clinoptilolite

Abstract

The present work concerns an equilibrium study of naturally occurring clinoptilolite as an ion‐exchange medium; the clinoptilolite has been used for the removal of the NH₄ ⁺ ion from a model aqueous effluent of the Landfill Leachate Assisted Froth Flotation (LLAFF) process. The other principal cations involved were sodium and calcium, and the anion was chloride. A number of experimental tests with constant ionic strength in solution were conducted; these were performed to further validate the feasibility of using clinoptilolite to remove NH₄ ⁺ ion from the LLAFF effluent. The experimental data obtained were well described by the law of mass action. A binary‐component equilibrium study revealed a value for the binary separation factor α_{NH4 ⁺, Na⁺} of 5.5; this value was relatively unaffected by the total salinity under the experimental conditions. Values for the intra‐particle diffusion coefficient and the maximum ion‐exchange capacity were also obtained; the latter was affected by total salinity. Results from the binary‐component and multicomponent studies have revealed the selectivity of clinoptilolite for ammonium over other cations under the compositional conditions of the model LLAFF effluent: The selectivity sequence is K⁺ > NH₄ ⁺ > Na⁺ > Ca²⁺. The factors that influence the selectivity of clinoptilolite for NH₄ ⁺ in LLAFF effluent have been ascertained; in particular, it has been found that small quantities of Ca²⁺ in the effluent have a deleterious effect on both selectivity toward ammonium and ammonium ion‐exchange capacity.

Keywords:

• Ion‐exchange equilibrium
• Clinoptilolite
• Ammonium ion removal
• Aqueous effluent
• Mass action
• Separation factor
• Competing cations
• Selectivity sequence