Reutilização da sílica-gel como adsorvente para remoção de nitrato de águas

Abstract

Underground and superficial water contamination, such as lakes and rivers, by nitrates, come mainly from the excessive use of nitrogen fertilizers and from the inadequate disposal of animal, urban and industrial waste in the environment. The presence of nitrate in water can cause health risks to children and pregnant women, thereby, limiting the direct use of these resources to humane consumption, since this contaminant presents high solubility and stability, and conventional treatments are not able to remove it. Therefore, this essay proposed the study of a treatment to remove nitrate from water through adsorption technique, using as absorbent reused silica gel, after a cleaning process. First, it was made a cleaning process of silica gel used as sanitary sand for cats, in order to remove organic residues presented on it, and decontaminate it. The water in question was synthesized in lab to contain the determined concentration of nitrate. It was determined the zero loading point and it was defined pH to the adsorption tests. Adsorption tests were performed at three temperatures and four different concentrations. The adsorption kinetics and the thermodynamic parameters of the adsorption were determined. In the adsorption tests, the solutions presented balance in the first few minutes of contact and indicated that as higher is the initial concentration, higher will be the adsorbed amount. At 30 ºC the kinetic model of pseudo second order fitted better to the data. In the first adsorption minutes the adsorbed values are equivalent in relation to temperature, over time there is a decrease in nitrate removal with the decrease in temperature. The thermodynamic parameters indicate that the process is exothermic and physical in nature.