Adsorção de nitrogênio amoniacal empregando a zeólita Watercel ZE® modificada

Abstract

Disposal of effluents without treatment in water bodies and the presence of deepwater contaminants has been one of the main environmental problems of modern. The presence of ammoniacal nitrogen (NH3-N) is related to eutrophication of water bodies and the presence of nitrate (NO3 - ) and nitrite (NO2) in drinking water is related to diseases caused by harmful effects on the metabolism of living beings. The objective of this work was to evaluate the kinetics, equilibrium and thermodynamics of the ammoniacal nitrogen adsorption process using as an adsorbent the Zeolite Watercell ZE modified with alkaline NaOH treatment. The adsorbent was characterized by X-ray fluorescence (FRX), N2 physisorption analysis, scanning electron microscopy (SEM) with dispersive energy spectrometry probe (EDS) and surface charge as a function of pH. Balance batch studies and process thermodynamics (at temperatures of 30, 40 and 50ºC) were conducted, as well as kinetic studies employing different initial concentrations and temperatures. Characterization studies of the adsorbent were carried out and X-ray fluorescence (FRX) results were suggested, the predominance of the natural zeolite Clinoptilolite [𝐴𝑙6𝑆𝑖30𝑂72] 6− was suggested as the cation exchange base), which was supported by the results of low specific surface area, low pore volume and macroporosity, from the N2 fisistion analysis. Scanning electron microscopy (SEM) showed the formation of crystal aggregates and the coupled EDS probe confirmed the elements determined by FRX, in addition to showing good distribution on the surface of the material. The surface charge of the material was positive at pH < 5 and negative at pH > 9, with a zero load region between these values. The equilibrium of the process at temperatures between 30 and 50° C and initial pH between 4.0 and 8.0 was best represented by the Freundlich isotherm. For this conclusion, a non-linear regression strategy was employed in which the equilibrium constant was described as a function of temperature through thermodynamic relationships. The results showed the competition of H+ ions between adsorbent-adsorbate at pH 4, explained by the positive surface charge of the adsorbent and the cationic character of NH4 + . The process was spontaneous and favorable and the magnitude of ΔH° indicated the predominance of the mechanism of chemisorption. The adsorption kinetics were best described by the Elovich model, which reinforced the suggestion that the process consists of chemical adsorption. It is noteworthy from several tested conditions that the material capacity reached 149 mg g-1 at pH 8.0 and at 50°C, showing a promising material for application in the removal of ammoniacal nitrogen in aqueous solutions. Finally, the data and models obtained can serve as a basis for the design of NH4 + adsorption systems in wastewater.