Enhanced adsorptive removal of ammonium on the Na+/Al3+ enriched natural zeolite

Biological methods for removing ammonium from surface water are ineffective at low ammonium concentrations and temperatures. Herein, in combination with calcination, natural zeolite (NZ) is modified using sodium aluminate (SA, NaAlO2) to determine its ammonium removal efficiency. The NZ impregnated with a 0.50 M SA solution and treated with calcination at 573 K exhibits the best ammonium removal rate, which increases by 21.20% compared to that with NZ under the same conditions. Regeneration through the NaCl solution impregnation further improves the ammonium removal efficiency of the modified NZ. More adsorption sites are created through Na+–cation exchange and Al3+ engrafting into the NZ skeleton. The average pore size and mesoporous volume percentage are also increased. Ammonium adsorption onto the modified NZs is a diffusion-controlled endothermic process. The isotherm better fits the Freundlich model because of the coarse surface functionalized using SA and calcination. The effect of coexisting ions, pH, and dosage on ammonium adsorption is also determined.