Sorption of non-ionic organic pollutants onto a humic acids-zeolitic tuff adduct: Thermodynamic aspects Vincenzo Leone a , Pasquale Iovino a,b , Stefano Salvestrini a,b , Sante Capasso a,b,⇑ a Department of Environmental, Biological and Pharmaceutical Sciences and Technologies, Second University of Naples, Via Vivaldi 43, 81100 Caserta, Italy b Interuniversity Consortium ‘‘Chemistry for the Environment’’ (INCA), Via delle Industrie, 21/8, 30175 Venezia, Marghera, Italy highlights  We studied sorption of organic compounds onto a humic acids-zeolitic tuff adduct.  Sorption of hydrocarbon compounds was exothermic.  Sorption of hydroxyl compounds was endothermic.  Entropy increment during sorption may be related to release of solvating water.  Sorption/desorption could be controlled by operating on the temperature. article info Article history: Received 1 March 2013 Received in revised form 29 July 2013 Accepted 7 August 2013 Available online xxxx Keywords: Humic acids-zeolitic tuff adduct Non-ionic organic pollutants Sorption Isosteric enthalpy abstract Sorption isotherms from water solutions for toluene, cyclohexane, o-xylene, benzyl alcohol, phenol and cyclohexanol onto a humic acid-zeolite adduct were determined at 4, 14, 24 and 34 °C and utilized to cal- culate the isosteric enthalpy (D ads H i ) and isosteric entropy (D ads S i ) of the process. For hydrocarbon com- pounds, toluene, cyclohexane and o-xylene, both D ads H i and D ads S i were negative, the process was exothermic. In contrast, for hydroxyl compounds, benzyl alcohol, phenol and cyclohexanol, D ads H i and D ads S i were positive, the increase in entropy possibly reflecting the release of water molecules during sorption. The results suggest that sorption/desorption of either class of compounds could be controlled by operating on the temperature. Ó 2013 Published by Elsevier Ltd. 1. Introduction Environmental and health problems associated with the pres- ence of organic pollutants in groundwater and surface water have stimulated the research for efficient cleaning procedures. Sorption by natural or synthetic sorbents is a favored choice because of its relatively high efficiency, low cost, and simplicity. Activated carbon is the sorbent of most common application in liquid–solid sorption and consequently its sorbing properties for organic pollutants have been analyzed extensively, including kinetics and thermodynamic aspects (Al-Sarawy et al., 2005). Other sorbents widely used for the removal of organic pollutants are silica and zeolites (Martucci et al., 2012). Zeolites are naturally-occurring aluminosilicates char- acterized by high surface areas, high cation-exchange capacity, and a three-dimensional cage-like structure with channel apertures in the order of few angstroms (Newsam, 1986). Treatment with surfactants conferring a more hydrophobic character to the active surface significantly improves zeolite ability to bind organic com- pounds (Karapanagioti et al., 2005). Non-ionic organic pollutants tend to localize at the interface between hydrocarbon chains of the surfactant and water. The resulting sorption isotherms have a linear shape and, as expected, sorption efficiency increases with the octanol/water partition coefficient of the sorbate considered (Xie et al., 2012). Recently, a novel organo-zeolite adduct obtained by immobiliz- ing humic acids (HA) on the surface of natural zeolite crystals has been found to be an efficient sorbent for non-ionic organic pollu- tants dispersed in water (Leone et al., 2013). Humic acids are nat- ural polymers with a broad molecular-weight distribution and high chemical heterogeneity; produced in nature by the biological decomposition of organic matter, they consist of a skeleton of cross-linked aromatic blocks with abundant carboxylic and pheno- lic groups that confer the molecule an acidic character (Hayers, 1998). The HA-zeolite adduct combines the well known cation 0045-6535/$ - see front matter Ó 2013 Published by Elsevier Ltd. http://dx.doi.org/10.1016/j.chemosphere.2013.08.019 ⇑ Corresponding author at: Department of Environmental, Biological and Phar- maceutical Sciences and Technologies, Second University of Naples, Via Vivaldi 43, 81100 Caserta, Italy. Tel.: +39 (0)823274623; fax: +39 (0)823274605. E-mail addresses: vincenzo.leone@unina2.it (V. Leone), pasquale.iovino@ unina2.it (P. Iovino), stefano.salvestrini@unina2.it (S. Salvestrini), sante.capasso@ unina.it (S. Capasso). Chemosphere xxx (2013) xxx–xxx Contents lists available at ScienceDirect Chemosphere journal homepage: www.elsevier.com/locate/chemosphere Please cite this article in press as: Leone, V., et al. Sorption of non-ionic organic pollutants onto a humic acids-zeolitic tuff adduct: Thermodynamic aspects. Chemosphere (2013), http://dx.doi.org/10.1016/j.chemosphere.2013.08.019