Uptake of Fluoride by Al³⁺ Pretreated Low‐Silica Synthetic Zeolites: Adsorption Equilibrium and Rate Studies

Abstract

The removal of fluoride from single component aqueous solution using Al³⁺‐ pretreated low‐silica synthetic zeolites (Al‐Na‐HUD, Al‐HUD, Al‐F9, and Al‐A4) was studied. The effects of adsorbent mass, initial solution pH, and initial concentration on fluoride removal in a batch system were evaluated. Equilibrium data were simulated using simple isotherms such as the Freundlich (F), Langmuir‐Freundlich (LF), Redlich‐Peterson (RP) and Dubinin‐Radushkevitch (DR) isotherms. From the DR model, initial pH effects and desorption studies, it was considered that the fluoride adsorption onto the zeolites proceeded by ion‐exchange or chemisorption mechanism. In interpreting the kinetic results, reaction kinetics (using Elovich equation) and mass transfer processes (both external mass transfer and intraparticle diffusion) were considered. Equilibrium and kinetic results of fluoride adsorption onto the adsorbents demonstrated the following order of performance: Al‐Na‐HUD>Al‐F9> Al‐HUD>Al‐A4.

Keywords:

• Fluoride
• low‐silica zeolites
• adsorption
• equilibrium
• kinetics

Acknowledgement

The authors wish to express their sincere gratitude to Dr. Yoshitake Masuda and Prof. Kunihito Koumoto of the Department of Applied Chemistry, Nagoya University, for carrying out the zeta potential measurements. One of the authors, M.S. Onyango, thanks the Japanese Ministry of Education, Culture, Sports, Science, and Technology, for offering a scholarship for pursuing the present work.