Adsorptive removal of phosphate ions from aqueous solution using synthetic zeolite

Phosphate ions are responsible for the algal bloom in receiving water bodies and aesthetic problems in drinking water. From the environmental and economic points of view, management of such a contaminant and valuable resource is very important. The present paper deals with the removal of inorganic phosphate ions from aqueous solutions using synthetic HSZ 330 HUD Zeolite (Si/Al ratio: 2.75-3.25) and its Al3+-activated form (Al-HUD) as adsorbents. Equilibrium and kinetic experiments were performed to study the effects of operating conditions such as adsorbent mass, solution pH, coexisting ions, and initial concentration on either the capacity or the rate of phosphate uptake by the zeolites. As a result, it was found that the efficiency of phosphate removal by the zeolites increased with an increase in adsorbent mass and a decrease in solution pH. Outer-sphere complex-forming ions such as nitrate, sulfate, and chloride improved slightly the phosphate removal efficiency while fluoride ions, which form inner-sphere complexes with binding sites, reduced the phosphate uptake capacity of the sorption sites. Equilibrium data were well-fitted with Langmuir, Freundlich, and Dubbinin-Radushkevitch isotherms. In the kinetic study, mass-transfer processes in the external and internal matrix of the sorbent were considered. The overall adsorption process was assumed to be controlled by intraparticle diffusion.