Journal of Hazardous Materials 185 (2011) 107–111 Contents lists available at ScienceDirect Journal of Hazardous Materials journal homepage: www.elsevier.com/locate/jhazmat Sorption study of toluene and xylene in aqueous solutions by recycled tires crumb rubber Luis A. Alamo-Nole a , Oscar Perales-Perez a,b , Felix R. Roman-Velazquez a,∗ a Department of Chemistry, University of Puerto Rico, Mayagüez, Puerto Rico b Department of Engineering Science & Materials, University of Puerto Rico, Mayagüez, Puerto Rico article info Article history: Received 3 March 2010 Received in revised form 9 July 2010 Accepted 1 September 2010 Available online 15 September 2010 Keywords: Waste tire Crumb rubber Sorption Recycling Water treatment Scatchard plot abstract Sorption of toluene and xylene by tire crumb rubber (TCR) and its main components: carbon black (CB) and styrene-butadiene polymer (SBP) were evaluated. The 12 starting concentrations of adsorbates in aqueous solutions ranged from 0.05 mg/L to 100.0 mg/L. The amounts of CB and SBP used in the sorption tests were determined considering their typical contents in tire crumb rubber (30% and 60% w/w, respectively). Freundlich’s isotherms and Scatchard plot parameters suggested a two-step sorption process when TCR was used as the sorbent; whereas a single-step route was apparent when the sorption experiments were carried out with CB or SBP. Freundlich’s n parameter was estimated at 0.65 for CB and 1.0 for both TCR and SBP. A removal of 60% of toluene and 81% of xylene from starting 50 ppm solutions was attained in the first 30 minutes of contact using 5 g/L of TCR. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Despite existing environmental protection policies, severe water pollution events are still frequent worldwide. One of the sources of water pollution is petroleum derivatives. For example, high concentrations of aromatic compounds such as ethylbenzene, toluene and xylene have been detected in oil and gasoline spills [1]. These compounds can be mobilized into the aqueous phase, making the contamination problem even worse. It is known that exposure to toluene and xylene can cause disturbances in the central ner- vous system and damage to the kidneys and liver [2]. Accordingly, the maximum contaminant levels (MCL) established by the US- EPA for drinking water are 1.0 and 10 mg/L for toluene and xylene, respectively [1]. Several approaches to remove toluene and xylene from aqueous solutions have been reported; the use of granular activated charcoal (GAC) is the most common alternative. Other options include the use of zeolites, surfactant-modified zeolites and polymeric sorbents [3]. The prohibitive costs involved with the synthesis of the above mentioned sorbents limit their applicability to treat large volumes of polluted effluents. Evidently, the ideal sorbent should exhibit uptake capacities comparable to commercial products while being cost-effective. ∗ Corresponding author. E-mail address: roman felix@yahoo.com (F.R. Roman-Velazquez). It has been estimated that over 10 billion tires are discarded worldwide every year; in 2005, approximately 259 million tires were fabricated in the US. Although the market for the scrap tires utilizes around 80% of used tires, the remaining 20% is stockpiled or put in land fills [4,5]. Tire crumb rubber (TCR) consists of a complex mixture of elastomers including polyisoprene, polybutadiene and styrene-butadiene. Stearic acid (1.2%), zinc oxide (1.9%), extender oil (1.9%) and carbon black (31.0%), are also important components of tires [6]. Carbon black (CB) is used to strengthen the rubber, improve its abrasion resistance and reduce its degradation by UV rays [7]. This nanosize component should exhibit adsorption prop- erties similar to those of activated charcoal, a well known agent used to remove organic and inorganic compounds from aqueous and gaseous effluents [8,9]. Therefore, the levels of CB in waste tires should promote the removal of the targeted dissolved species through adsorption mechanisms [10–14]. Stearic acid could also behave as an ionic exchanger because the carboxylic group can pro- mote ion exchange with metal ions. Moreover, non-polar organic pollutants are expected to interact with the rubber matrix via van der Waals interactions [15]. The present study addresses the evaluation of TCR (as a com- posite material) and its main components as sorbents from organic pollutants in water. CB and SBP have been evaluated separately and their sorption capability has been compared with those from actual TCR in order to understand their role in the overall sorption process. To our knowledge no prior studies about the effect of TCR compo- nents on its sorption capability have been reported. Adsorption data 0304-3894/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2010.09.003