Zeolite modification for adsorptive removal of nitrite from aqueous solutions

Abstract

Considering the occurrence of nitrite in drinking water sources, this paper investigated the modification of natural zeolite by acid, base, salt, organic surfactant, calcination and ultrasonication for eliminating nitrite from aqueous solutions. The structural and surface properties were analysed by X-ray diffraction (XRD), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) and nitrogen adsorption-desorption isotherm, and were used to explain the nitrite adsorption capacities of the zeolites. The results show that except acid modification, the rest measures did not impose notable influences on the zeolite properties. Modification of zeolite by acids markedly increased the specific surface area and strongly protonated the material, which greatly favored the nitrite adsorption onto the resulting zeolite. The adsorption isotherms were in good agreement with Langmuir-Freundlich models, and indicated an endothermic process. At 25 °C, the nitrite adsorption capacity of the zeolite modified by 0.75 mol L−1 of H2SO4 for 12 h (ACMZ) was 54.5 mg N g−1, being over 7-fold higher than that by the raw zeolite. The adsorption of nitrite onto ACMZ followed pseudo-first order kinetics. These facts suggest that the uptake of nitrite by acid modified zeolite was a chemical adsorption in nature.