Aplicação de argilas bentonitas modificadas na remoção de atrazina em sistema aquoso

Abstract

Pesticides application has been spread significantly as agricultural productivity and crop diversity develop. It is worth mentioning that such application has affected even non-target organisms and caused severe negative impacts on the environment. Atrazine is an herbicide widely applied for broadleaf and grassy weeds in corn, sugarcane, and sorghum crops. It is considered toxic due to its long half-life, high mobility, high leaching capacity, and bioaccumulation power. It is classified as Class III in toxicity (intermediate level) and Class II in environmental hazard (very dangerous). Atrazine has a maximum allowed contaminant level of 2 µg L-1 in drinking water in Brazil and is forbidden in the Europe Union. It is related to several diseases in humans and animals, mainly due to its endocrine-disrupting properties. Its environmental contamination has happened due to its incorrect disposal after its application managements in agriculture, wind and rain actions, by surface runoff, and soil leaching, which allow this herbicide to reach surface and groundwater. Several techniques are applied to remove pesticides, such as advanced oxidation processes, electrochemical processes, bioremediation and adsorption. Adsorption is commonly applied due to its ease, high efficiency, and low cost. The most important adsorbents are activated carbon, biochar, alumina, organic resins, and clays. Bentonite clays, particularly, are relevant for their large surface area, chemical stability, high cation exchange capacity, and availability. Clay modification techniques have been applied to enhance adsorption efficiency in treating contaminated water. Studies have shown improved adsorption capacity due to increased surface area and porosity of those studied clays. Thus, this study aims to modifying bentonite clay to produce an effective adsorbent for atrazine removal from aqueous solutions. Bentonites samples were provided by T-Minas company and modified by acid and thermal treatments, as well as the best changing conditions for adsorption were evaluated. Equilibrium and adsorption kinetics tests were carried out to evaluate clays adsorption capacity. Then, a mathematical modeling was applied to investigate the mechanism that best controlled the atrazine adsorption process. Characterization was carried out by X-ray diffraction (XRD), scanning electron microscopy (SEM, identification of surface functional groups, present by Fourier-transform infrared spectroscopy (FTIR).