Development of chemically modified clinoptilolite granules for enhanced ammonia removal

Zeolites are widely studied and applied in water and wastewater treatment owing to their favorable adsorption properties. Among the various types of zeolites, clinoptilolite (hereafter referred to as Clin) is one of the most abundant natural forms. However, despite its abundance, natural Clin relatively low efficiency for ammonia removal, which has motivated chemical modification to improve its performance. In this study, a chemically modified granular adsorbent with improved adsorption performance was developed through the chemical modification of Clin using sodium chloride (NaCl), magnetite (Fe₃O₄), sodium aluminate (NaAlO₂) and sodium hydroxide (NaOH) to improve ammonia uptake. Among the tested modifications, NaAlO₂‑modified Clin (NaAlO₂/Clin) exhibited the highest adsorption capacity under the examined conditions. It reached up to 39.84 mg/g at pH 8, an adsorbent dosage of 4 g/L, a contact time of 120 min, and an initial ammonia concentration of 100 mg/L. To enhance practical applicability, NaAlO₂/Clin was granulated using polyvinyl alcohol (PVA) as a binder, resulting in a mechanically stable granular adsorbent suitable for handling and reuse, with a maximum adsorption capacity of 24.42 mg/g. The adsorption data for both powdered and granular forms were well described by the Langmuir and Freundlich isotherm models. Furthermore, the granules retained moderate reusability over multiple regeneration cycles, which suggests their potential applicability for ammonia removal in wastewater treatment.