Chemical Engineering Journal 168 (2011) 1024–1031 Contents lists available at ScienceDirect Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej Mineralogical identification, spectroscopic characterization, and potential environmental use of natural clay materials on chromate removal from aqueous solutions Mabrouk Eloussaief a,∗ , Nejib Kallel b , Abdelghani Yaacoubi c , Mourad Benzina a a Laboratoire Eau, Energie et Environnement (LR3E), Code: AD-10-02, Ecole Nationale d’Ingénieurs de Sfax, Université de Sfax, B.P1173.W.3038, Sfax, Tunisia b Unité de Recherche “Geoglob”, Code: 03/UR/10-02, Faculté des Sciences de Sfax, Université de Sfax, B.P802.W.3038, Sfax, Tunisia c Laboratoire de Chimie Organique Appliquée, Unité d’Analyse et de Contrôle Qualité, Département de Chimie, Faculté des Sciences Semlalia, B.P2390, Marrakech, Morocco article info Article history: Received 27 October 2010 Received in revised form 18 January 2011 Accepted 20 January 2011 Keywords: Clays Characterization Low-cost adsorbent Chromium adsorption Model abstract The first part of this study is a chemico-mineralogical characterization of two Cretaceous sedimentary clays taken from Aleg formation of Jebel M’rhila (Tunisia). The clay deposits were localised in different levels; the uppermost (C1) and the lowermost (C2). This research has been carried out by using X-ray diffraction (XRD), infrared spectroscopy (IR), thermal analysis (TG and DT), observations with scanning electron microscopy (SEM) and analytic techniques. The second part of this study consists in evaluating the adsorption capacity of the natural clays in order to facilitate their industrial or environmental appli- cations. At 20 ◦ C and at pH 5, the maximum Cr(VI) adsorption capacities were 10.9 and 4.5 mg g -1 for C1 and C2, respectively. Langmuir, Freundlich and Dubinin–Radushkevich (D–R) isotherm models were used to evaluate the equilibrium data. The Langmuir isotherms fit better the experimental data. The results which were obtained can be introduced in data base for designing an adsorption process using clay, as a low-cost adsorbent for the treatment of the Cr(VI) rich wastewater. © 2011 Published by Elsevier B.V. 1. Introduction Tunisian clays have been the subject of several studies. How- ever, the most part of the reported works dealt with the knowledge of their genesis and/or particular geological features [1–4]. A little attention has been paid to their physicochemical properties [5–7]. Thus, we have undertaken a research program in order to determi- nate such properties, because they may be useful to predict the behaviour of these natural materials. Eventually, they allow the extension of their uses which are limited actually elaboration of traditional products, such as earthen pots and rustic bricks. Owing to their interesting physicochemical properties (lamel- lar structure, high surface area and large cation exchange capacity), clay materials have great potential to fix pollutants, such as heavy metals [8–12]. In this respect, because of their toxicity applica- tions: trivalent chromium Cr(III) and hexavalent chromium Cr(VI) are two common existing oxidation states of chromium found in the environment. Public concerns are mostly related to Cr(VI) due to its high toxic nature to biological systems [13,14]. Major sources of chromium are effluents from electroplating, metal finishing, chromium mining pigments, leather tanning, wood protection, ∗ Corresponding author. Tel.: +216 22 766 584; fax: +216 74 275 595. E-mail address: eloussaiefmabrouk@yahoo.fr (M. Eloussaief). electrical and electronic equipments manufactures and catalysis [15]. Treatment of the Cr effluents poses a serious problem to ecosystems and cause great public concern. Cr(VI) is a powerful carcinogenic agent which modifies the DNA transcription [16]. The recommended limit of chromium in potable water is 0.05 mg L -1 [17]. Several methods have been applied for the removal of heavy metals in wastewater. We can take as examples: chemical pre- cipitation, membrane filtration, ion-exchange, solvent extraction, dialysis/electrodialysis, reverse osmosis, flotation and adsorption [18–21]. Among these methods the adsorption method is more commonly used, thus several studies have been done various low cost adsorbents [22–24,15] and natural materials such as clay are effective adsorbents for the removal of heavy metals. This research paper reports the results of a chemico- mineralogical, kinetic and equilibrium study on tow natural clay materials for Cr(VI) removal application. Whereas the effectiveness of adsorption relies much on operational conditions, parameters that may affect the adsorption including pH, temperature and ini- tial concentration were evaluated. The results can be introduced in data base for using this material as a low-cost adsorbent for the treatment of Cr(VI)-rich effluents. 2. Geological setting The samples come from Jebel M’rhila-Kasserine, Tunisia. Jebel M’rhila area (Fig. 1) shows a 25 km-long NNE-SSW-oriented Atla- 1385-8947/$ – see front matter © 2011 Published by Elsevier B.V. doi:10.1016/j.cej.2011.01.077