Estudo da adsorção do corante reativo preto 5 sobre carvão ativado: caracterização do adsorvente e determinação de parâmetros cinéticos e termodinâmicos




In this work the adsorption of black five reactive dye was investigates using activated carbon as adsorbent. The results emphasize the kinetic and thermodynamic parameters of this process. The characterization of the adsorbent showed the following results: surface area (BET) = 439,28 m2/g, micropores volume (DR) = 0,22 cm3/g and width of the micropores (DR) = 67,19 Å. These data justify the adsorption properties of the activated carbon. The zeta potential of activated carbon was negative for all range of pH investigated. The adsorption studies were carried out in a thermostatic bath using 150 rpm of agitation. For a 50 cm3 dye solution, 1,0 g of the activated carbon was added. The pseudosecond order model fitted the kinetic results and the diffusion intraparticle is involved in the adsorption mechanism. For the thermodynamic equilibrium studies, the results show better adjustment to the Langmuir equation. An elevation in the temperature of the system provokes increase in the amount adsorbed and also in the time for the system to reach the equilibrium. The pseudo-second rate constant decreases with increasing temperature, while the half life time increases. The activated energy value, Ea = -27,83 kJ.mol-1, shows that the process is of physical nature. The activation parameters obtained from Eyring equation were: H* = -29,68 kJ.mol-1, S* = -319,77 J.mol-1.K-1 and G* = 65,61 kJ.mol-1 (25 C). An increase in the initial concentration of the dye resulted in the increasing the adsorbed amount of the dye and also in the time necessary for the system to reach the equilibrium. The rate constant diminishes when the initial dye concentration is increased until a certain value of C0. The addition of an electrolyte to the adsorption system caused an increase in the dye adsorbed amount and a decrease in the rate constant. The pH does not influence significantly the amount of dye adsorbed in the equilibrium, however, an increase of the rate constant is registered when pH is elevated. The thermodynamic parameters: Hads = 10,53 kJ.mol-1, Sads = 41,02 J.K-1.mol-1 and Gads = -1,69 kJ.mol-1 (25 C), indicate that the process is of endothermic nature, spontaneous and favorable. The study of dye stability shows that its structure is not altered along the time of the adsorption. Finally, the dessorption studies involving different medium showed that ethanol was the only solvent to present some recovering of the dye


adsorption carvão ativado carbono ativado; corantes - absorção e adsorção processos químicos parâmetros cinéticos e termodinâmicos adsorção kinetic and thermodynamic parameters activated carbon quimica

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