Desenvolvimento de carvão ativado a partir de tabaco visando remediação de águas contaminadas por metais tóxicos

Abstract

Water resources are fundamental elements in the development of living beings and when contaminated can cause problems of environmental, economic and social proportions. Numerous alternatives allow the remediation of this environmental compartment, among them the adsorption. It can be an economically feasible process and it presents high efficiency in the removal of metals. A material with great potential for pollution, which currently does not have an environmentally adequate destination, and can be transformed into adsorbent for decontamination of water resources is the cigarette that is a product originated from seizures carried out by the Federal Police in border regions. An alternative that can solve the problem of disposal of these wastes and subsequently its application in a sustainable way in the remediation of contaminated water is the production of modified adsorbents (activated carbon) using as precursor material the tobacco. Thus, the present work aims to transform these pollutant residues into sustainable adsorbents in the form of activated carbon aimed the remediation of water compartments contaminated by toxic metals (Cd and Pb). For this purpose, carbons were developed under different activation methods (thermal, physical and chemical) and with different modifying agents (NaOH, ZnCl2, 1 mol L-1 H3PO4). After the development of the activated carbons, the materials were characterized by chemical composition, zero load point (pHPCZ), scanning electron microscopy (SEM), infrared spectra (FT-IR), porosimetry and adsorption tests by means of dose and pH studies, kinetics, equilibrium, thermodynamic and desorption. According to the chemical characterization of the materials, it was observed that the in natura material presents concentrations of toxic metals that remained present in the activated carbon. In addition, the SEMs allowed to verify that the different activations were responsible for changes in the structural formations in the materials, being verified tubular and spongy structures. By the FT-IR it is observed the presence of hydroxyl, phenolic, aromatic and carboxylic groups in the materials and carbonate group only in the activated carbon conferring characteristics favorable to the adsorption. The activating solutions changed the zero load point of the tested adsorbents being observed the follow values: 5.40 for T in natura, 10.39 for CT Biochar, 11.11 for CT in natura + CO2, 9.59 for CT H3PO4 + CO2, 7.74 for CT ZnCl2, 9.05 for CT ZnCl2 + CO2, 12.84 for CT NaOH and 10.86 for CT NaOH + CO2. The optimal adsorption conditions of the Cd2+ and Pb2+ ions were: pH: 5.0; dose of the adsorbent: 4 g L-1 and equilibration time of 45 min for all the adsorbents tested. In general, the Langmuir, Freundlich and Sips models fit the experimental data, suggesting adsorption in mono and multilayer. The pseudo-second order model suggested the predominance of chemosorption in the materials. The removal of the contaminants presented low desorption rates, corroborating with the results of thermodynamics. The materials developed have potential for remediation of water contaminated with Cd and Pb higher than in natura material.