Adsorção de ácido acetilsalicílico em solução aquosa por carvão ativado e bagaço de cana-de-açúcar

Abstract

Among the environmental contaminants, mention should be made of the drugs, frequently found in low concentrations in the water bodies in the order of ng.L -1 and mg.L -1, making it difficult to remove them in the conventional stages of water treatment for drinkable water. Adsorption in activated carbon has been studied as a complement to these steps. In this context, the objective of this work was to investigate the adsorption of acetylsalicylic acid (ASA) in sugar cane bagasse, in natura and carbonized, as an alternative to commercial activated charcoal and to evaluate the desorption potential of these adsorbents. Chemical and physical characterization of the adsorbent materials was carried out, as well as kinetic studies and isotherms at pH 2.0, 3.5, pHPCZ and 10.0, adsorption / desorption, and thermodynamics. In addition, spectra were determined in the infrared region by FTIR and by ATR, pHPCZ, functional groups by the Boehm method, micrographs (MEV / EDs) of these adsorbents. Norit® 1240 W activated carbon (CAN) presented microporosity and a higher specific surface area compared to the sugar cane bagasse in natura (BCN) and carbonized (BCC). Carboxylic, phenolic, lactonic and basic groups were not very sensitive to the Boehm method for CAN. The pHpcz values were 7.2, 5.9 and 7.02 for CAN, BCN and BCC, respectively. The pseudo-second order kinetic model better fitted the CAN and BCC and Langmuir-Freundlich experimental data to the CAN data for the studied pH values and BCC at pH 2.0 and Freundlich for BCC at pH 3.5. The highest amounts adsorbed on CAN and BCC were in acid midst due to the attraction between the AAS molecule and the surface of the adsorbent and may be related to chemistry. The thermodynamic study showed an increase in adsorbed amount of AAS at 45 ºC for adsorbents at pH 2.0. Negative ΔG° values indicated spontaneous and favorable process occurrence. Positive ΔS° and ΔH° values suggest an increase in the solid / fluid interface disorder and endothermic nature. The adsorbent most efficient in the removal of AAS was Norit® 1240 W activated carbon in acid pH (92.88 and 77.80 mg.g -1), and the alternative of using sugarcane bagasse was not viable. The desorption study of the adsorbents, using deionized water as a regenerating agent, indicated a better fit with the kinetic model of pseudo-second order for the CAN. The desorption velocity was higher than that observed for adsorption with these adsorbents. The CAN and BCC had no possibility of regeneration as observed in the adsorption / desorption cycles.