Preparation of colloidal hydrated alumina modified NaA zeolite derived from rice husk ash for effective removal of fluoride ions from water medium

Alumina is found to be a good adsorbent for the removal of fluoride. In the present study, rice husk ash-derived NaA zeolite has been modified with colloidal hydrated alumina in a cost-effective process for efficient removal of fluoride ions. The prepared NaA zeolite powder was added into colloidal hydrated alumina under stirring at 70°C/2 h followed by drying at 100°C/6 h to obtain modified zeolite. The product reveals enhanced adsorption efficiency (95–99%) for the removal of fluoride ions at wide ranges of adsorbate concentration (~5–200 mg/L), adsorbent concentration (0.5–10 g/L), pH (3–10), and temperature (30–70°C). Regeneration study shows that adsorption remained >90% up to third cycle followed by gradual decrease of adsorption for consecutive cycles. Kinetics study of fluoride adsorptions shows best fit for pseudo-second-order model demonstrating chemisorption process through a monolayer formation. The adsorption isotherm reveals that Langmuir isotherm is the best fit model indicating maximum adsorption capacities of 104.16, 68.12 and 36.13 mg/g for the adsorbent doses of 0.5, 1 and 2 g/L, respectively. Colloidal hydrated alumina modified NaA zeolite derived from rice husk ash could be utilized as low cost adsorbent for effective removal of fluoride ions from water.