Separation Science and Technology, Vol.41, No.4, 683-704, 2006
Uptake of fluoride by Al3+ pretreated low-silica synthetic zeolites: Adsorption equilibrium and rate studies
The removal of fluoride from single component aqueous solution using Al 3+ - 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.