Simultaneous removal of NH4+ and PO43- from simulated reclaimed waters by modified natural zeolite. Preparation, characterization and thermodynamics

Natural zeolite was modified by NaCl, AlCl₃ and thermal treatment for the removal of NH₄⁺ and PO₄³⁻ ions. The characteristics of the modified zeolite (AlZ) and its mechanism for the NH₄ ⁺ and PO₄³⁻ removal were studied and compared. The results showed that the surface area and the Na⁺ and Al³⁺ content increased whereas the content of Ca²⁺, K⁺ and Mg²⁺ decreased after zeolite modification. On natural zeolite when activated with the 1 M NaCl and 10 cm³ /g of pillaring dosage, high adsorption efficiencies for the NH₄ ⁺ (97.80%) PO₄³⁻ (98.60%) were obtained. The results of various analyses indicated that the Na⁺ exchange is the main mechanism for NH₄ ⁺ removal whereas the adsorption mechanism for PO₄³⁻ followed the complexation with Al–OH groups present in the AlZ. In addition, the kinetics study showed that the adsorption of NH₄⁺ and PO₄³⁻ followed pseudo-second order model while the adsorption isotherm of NH₄ ⁺ and PO₄³⁻ is consistent with the Langmuir isotherm model. Moreover, the Gibbs free energy change for the simultaneous removal of the ions indicates that NH₄ ⁺ is adsorbed faster compared to PO₄³⁻. The simultaneous removal of NH₄ ⁺ and PO₄³⁻ by AlZ adsorbent is cost effective in water treatment at low ion concentrations.