Pedro Alonso-Davila Oliva L. Torres-Rivera Roberto Leyva-Ramos Raul Ocampo-Perez Centro de Investigacion y Estudios de Posgrado, Facultad de Ciencias Quimicas, Universidad Autonoma de San Luis Potosi, San Luis Potosi, Mexico Research Article Removal of Pyridine from Aqueous Solution by Adsorption on an Activated Carbon Cloth Pyridine is a very toxic pollutant that has to be removed from wastewater. In this work, adsorption of pyridine on activated carbon cloth (ACC) is studied as a possible alterna- tive for eliminating pyridine from aqueous solution. The ACC was produced from polyacrylonitrile. The adsorption equilibrium data of pyridine on ACC was obtained in a batch adsorber. The experimental data was interpreted with the isotherms of Langmuir, Freundlich, and Prausnitz-Radke (PR), and the PR isotherm better represented the experimental data. The capacity of ACC for adsorbing pyridine was favored increasing the solution pH from 3 to 6, and this effect was due to the p–p dispersive and electrostatic interactions between the pyridine species in solution and the surface complexes of ACC. The modified Langmuir model fitted reasonably well the influence of pH on the adsorption capacity. In this model was assumed that both neutral pyridine and pyridinium were simultaneously adsorbed on ACC accordingly to the experimental results. The adsorption capacity was almost independent of tempera- ture. The reversibility study revealed that 75% of the pyridine can be desorbed from ACC indicating that part of the pyridine was irreversibly adsorbed, and possibly chemisorbed. Keywords: Activated carbon cloth; Adsorption; Desorption; Pyridine Received: January 28, 2011; revised: June 7, 2011; accepted: June 27, 2011 DOI: 10.1002/clen.201100049 1 Introduction Pyridine is a pale, combustible and malodorous liquid, volatile, and very soluble in water. Pyridine and its derivatives are commonly used as intermediates in the manufacture of herbicides, insecticides, and pharmaceuticals [1, 2]. It is also employed as a solvent for paint, rubber products, adhesives, and waterproof compounds [1, 2]. Pyridine has been detected in both surface and groundwater due to wastewater discharges from various industrial activities [3]. The con- centration of pyridine in the wastewater from a pharmaceutical plant ranged from 20 to 300 mg/L [2]. Biodegradation of pyridine in aqueous solutions can be very slow and the presence of pyridine can cause serious pollution problems to diverse ecosystems [3]. Water pollution caused by toxic organic compounds has moti- vated the development of new removal technologies. The polluted waters can be treated by various processes such as biological, con- ventional (thermal oxidation, chlorination, and ozonation), and advanced oxidation methods. However, in some cases these pro- cesses are unsatisfactory because they are expensive and inefficient or their intermediate reaction products are even more toxic than the original pollutants. Adsorption has been demonstrated to be an excellent alternative for treating and purifying wastewater. The activated carbon is the most commonly used adsorbent because of its great capacity for adsorbing diverse organic compounds such as dyes, heavy metals, pesticides, pharmaceuticals, and surfactants [4–7]. Several materials have been tested to adsorb pyridine from water solutions. Among these adsorbents are spent Rundle oil shale [8] and combusted oil shale [9], rice husk ash (RHA) [10], bagasse fly ash (BFA) [2], granular activated carbons prepared from coconut shell (CSAC) and coconut shell fibers [11], and peanut shells activated carbon (PSAC) [12], strong acid ion exchange resins [13], natural and syn- thetic apatites [14], activated carbon cloth (ACC) [11], and oxidized carbon nanotubes (CNTs) [15]. The capacity for adsorbing pyridine was considerably dependent upon the nature of the adsorbent and its preparation procedure as well as the solution pH and temperature. The adsorption capacities of the activated carbons from coconut shells were substantially increased by raising the solution pH from 2 to 6 and remained almost constant in the pH range 6–10 [11]. The pyridine adsorption capacity of oxidized and pristine CNTs, and BFA exhibited a maxi- mum at pH 8.55 [15] and pH 6 [2], respectively, whereas the capacity of RHA for adsorbing pyridine was not practically dependent upon solution pH [10]. In all these works, the dependence of the adsorption capacity on the solution pH was argued using the initial pH, but the solution pH changed during the adsorption of pyridine. Bouyarmane et al. [14] observed this behavior in the retention of pyridine on apatites. The adsorption equilibrium was reached at the final pH, and the results have to be argued using the final pH. Correspondence: Dr. R. Leyva-Ramos, Centro de Investigacion y Estudios de Posgrado, Facultad de Ciencias Quimicas, Universidad Autonoma de San Luis Potosi, Avenida Dr. Manuel Nava No. 6, San Luis Potosi, SLP 78210, Mexico E-mail: rlr@uaslp.mx Abbreviations: AC, activated carbon; ACC, activated carbon cloth; BFA, bagasse fly ash; CNTs, carbon nanotubes; CSAC, coconut shell activated carbon; ML, modified Langmuir; PAN, polyacrylonitrile; pH PZC , pH of point of zero charge; PR, Prausnitz-Radke; PSAC, peanut shells activated carbon; RHA, rice husk ash Clean – Soil, Air, Water 2012, 40 (1), 45–53 45 ß 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.clean-journal.com