Removal of ammonium from aqueous solution by three modified molecular sieves: a comparative study

Molecular sieves (Ms) modified either by treatment with a NaCl solution, or by microwave treatment, or by both NaCl and microwave treatment were employed to promote the removal of ammonium from aqueous solution. Parameters such as NaCl concentration, NaCl stirring time, microwave power and microwave irradiation time were optimized with respect to ammonium removal. The specific surface area, structural characteristics and porous properties of both raw and modified Ms were studied using N₂ adsorption-desorption, scanning electron microscopy, X-ray fluorescence, and energy dispersive spectroscopy. The results demonstrate that NaCl-microwave modified Ms had the highest capacity to remove ammonium (4.32 mg g^-1), followed by NaCl modified Ms (3.41 mg g^-1), microwave modified Ms (3.40 mg g^-1), and raw Ms (2.37 mg g^-1). Optimization of the modification conditions using a response surface methodology resulted in a 1.94 mol L^-1 NaCl solution, a microwave power of 400 W and an irradiation time of 5.1 min. NaCl-microwave modification effectively increased the removal capacity of ammonium by increasing the sodium content, modifying the surface morphology, and enlarging both the surface area and the pore volume for the Ms.