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In this work, the adsorption of Pb(II) from aqueous solution was investigated on various types of activated carbon fibers (ACFs) manufactured from polyacrylonitrile and phenolic resin. The textural and physicochemical properties of the ACFs were determined by the N 2 -BET method and acid-base titration. The experimental adsorption equilibrium data of Pb(II) on the ACFs were obtained in a batch adsorber, and the Langmuir isotherm model better fitted the experimental data. The effects of the type of ACF and precursor of ACF, solution pH and temperature upon the adsorption of Pb(II) on the ACFs were examined in detail. The adsorption capacity was highly dependent upon the precursor of ACF. The Pb(II) adsorption capacity of the ACFs augmented when the solution pH and temperature were increased from 2 to 4 and from 288 to 308 K, respectively. The effect of the pH was attributed to the interactions between the surface of the ACF and Pb 2+ ions present in the water solution. The Pb(II) adsorption capacity of the ACFs was enhanced by oxidation with HNO 3 solution and the enhancement factor was between 1.1 and 1.4. The reversibility of the adsorption of Pb(II) was investigated by first adsorbing Pb(II) on an ACF and then desorbing the Pb(II). It was noticed that Pb(II) was substantially desorbed from ACF while reducing the solution pH to 2. It was concluded that the Pb(II) was mainly adsorbed on the ACFs by chemisorption, electrostatic interactions and ion exchange.

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Palabras clave: materiales lignocelulósicos, mecanismo de bioadsorción, sitios activos, microprecipitación RESUMENEl plomo ha sido reconocido como uno de los metales más tóxicos por su efecto negativo sobre el ambiente. En el presente trabajo se evaluó el uso potencial de residuos de Agave lechuguilla Torr. (lechuguilla) y Yucca carnerosana (Trel.) McKelvey (yuca) procedentes de la industria ixtlera para remover iones Pb (II) presentes en solución acuosa. Los datos del equilibrio de bioadsorción mostraron que al aumentar el pH de la solución de 2.0 a 5.0, la capacidad de bioadsorción de ambos materiales se incrementa. Este efecto se explicó considerando que la carga superficial negativa de estos materiales es mayor al aumentar el pH y por ello se favorece la remoción de Pb (II). El efecto de la temperatura de la solución en las isotermas de bioadsorción, expuso la naturaleza endotérmica del proceso. La energía libre de Gibbs y la entropía calculada (ΔG° y ΔS°) indicaron la espontaneidad de la bioadsorción y la afinidad del Pb (II) en solución por los bioadsorbentes, respectivamente. La variación de las capacidades de bioadsorción de la lechuguilla y la yuca se atribuyó a la diferencia en el contenido de sitios ácidos y lignina, lo que condujo a la presencia de diversos mecanismos de bioadsorción. En ambos materiales, la bioadsorción de Pb (II) ocurre por los mecanismos de interacciones π-catión, atracciones electrostáticas e intercambio iónico; además en el caso de la lechuguilla se evidenció un proceso de microprecipitación.Key words: lignocellulosic materials, biosorption mechanism, active sites, microprecipitation ABSTRACT Lead has been recognized as one of the most toxic metals due to its negative effect on the environment. In the present work, the potential use of Agave lechuguilla Torr.

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