Adsorção de atrazina: avaliação de adsorventes, cinética e equilíbrio

Abstract

Raising awareness of environmental issues resulting from the use of pesticides in agricultural production encouraged the search for methodologies for the treatment and removal of these compounds from the environment. In view of the use of the herbicide Atrazine in crops such as corn and sugar cane, and its legalized use in Brazil, treatment technologies have been sought. With regard to environmental contamination from washing sprays, the adsorption process has gained prominence, as it is an organic compound. With this, sustainable adsorbents have been evaluated, citing coconut and rice husk as biocarbons as an example. In addition to acting as biocarbons, the management of these residues in the agricultural industry is essential in terms of proper final destination. Thus, the present study aimed to test different adsorbents for the removal of atrazine from synthetic effluent, the CA of coconut and rice husk, for both, yet, an additional process of chemical activation was proposed The study of the kinetics and the adsorption balance was carried out with the use of coal that showed greater capacity for adsorption in the experiment carried out. The methodology applied for the balance tests consisted of batch experiments, at temperatures of 25, 35 and 45 ºC, in concentrations ranging from 5 to 50 mg L-1 in a fixed adsorbent mass of 0.1 g for 600 minutes. For kinetics, the time varied from 0 to 660 minutes, with a fixed initial concentration of 30 and 10 mg L-1 and a constant temperature of 35 °C. The analysis methodology was performed by LC-ESI-MS, equipped with standard atrazine identification methodology. Still, the experimental data were evaluated by means of mathematical modeling for kinetic and equilibrium models. It was proposed to evaluate the precision and accuracy of the models tested by the Akaike criterion. The preliminary evaluation of adsorbents allowed to list that the CA of rice husk is the most suitable for the adsorption of atrazine in the tested conditions, being this adopted for the kinetic and equilibrium study. The Freundlich isotherm (R2 = 0.9342 and AICc = 54.9) is able to represent the isotherm of atrazine adsorption with rice husk activated carbon under the conditions employed. It is concluded from the thermodynamic study that the adsorption of atrazine with activated charcoal from rice husk is spontaneous and favorable. In the evaluation of kinetics, the pseudo first order model, PFO, was the one that obtained the best results in adjusting the data (R2 = 0.9857 and AICc = -7.6). Therefore, it is possible to use rice husk CA in the adsorption of atrazine in projects that adapt the methodology to larger scales.