Adsorção em batelada do herbicida 2,4-d pelos carvões ativados de resíduos de biomassa amazônica

Abstract

The use of chemical pesticides is common for agricultural, industrial and domestic purposes. One herbicide widely used in agriculture is 2,4-D, 2,4-dichlorophenoxyacetic acid, which not only further increases the chances of surface and groundwater contamination, but also has a significant degree of toxicity. Its use leads to contamination of surface and groundwater, and consequently exposure of aquatic and terrestrial species, such as humans. Therefore, the treatment of this water is necessary to avoid contamination of the environment in which the herbicide 2,4-D is used and, consequently, to prevent contamination of the living beings that are part of this ecosystem. One way of treating and purifying effluents is through the batch adsorption method, a process in which a solid adsorbent interacts for a certain period of time with the herbicide molecules present in the effluent, adsorbing them onto its surface. The aim of this study was to evaluate the adsorption efficiency of 2,4-D by activated carbon from Amazonian biomass (açaí bark and cupuaçu stones) by determining its adsorptive capacity in batches to remove the herbicide 2,4-D from contaminated water. The characterizations, such as scanning electron microscopy and BET isotherm, showed that the adsorbents studied had porous morphologies and a high surface area. Cupuaçu activated carbon had a pHpzc of 8.31, favoring adsorption of the herbicide at neutral pH. On the other hand, açaí charcoal had a pHpzc of 3.85, which is lower than the pKa of the herbicide, making it impossible to use it as an adsorbent for 2,4-D. The study of adsorption kinetics fitted the pseudo-second order model, indicating that the overall adsorption rate of the experiment is equal to the square of the available active sites of the adsorbent. The highest adsorption capacity value in the experiment was 64.103 mg.g-1 at pH 7 and 40 minutes equilibrium time at 298 K. The Langmuir isotherm was the best fit to the experimental data, suggesting the occurrence of chemisorption, with the formation of a single monolayer, energetically homogeneous sites and the process reversible only at high energies.