Journal of Hazardous Materials 250–251 (2013) 454–461 Contents lists available at SciVerse ScienceDirect Journal of Hazardous Materials jou rnal h om epa ge: www.elsevier.com/locate/jhazmat Chromium(VI) removal via reduction–sorption on bi-functional silica adsorbents Nataliya Zaitseva a,b , Vladimir Zaitsev b , Alain Walcarius a,∗ a Laboratoire de Chimie Physique et Microbiologie pour l’Environnement, UMR 7564, CNRS–Université de Lorraine, 405, rue de Vandoeuvre, F-54600 Villers-les-Nancy, France b Analytical chemistry department, Taras Schevchenko National University, 60 Volodymyrska Str., Kiev, Ukraine h i g h l i g h t s ◮ SH-functionalized silica is able to reduce Cr(VI) into less toxic Cr(III) species. ◮ Cr(III) can bind to ethylenediaminetriacetate groups in bi-functionalized sorbent. ◮ The reduction–sorption process is very fast and pH dependent (optimum: pH 1–3). ◮ Cr(III) binding is stronger than with sulfonate groups (possible column sorption). ◮ Good chromium sorption performance was observed in the presence of interference. a r t i c l e i n f o Article history: Received 7 November 2012 Received in revised form 7 February 2013 Accepted 11 February 2013 Available online 19 February 2013 Keywords: Grafted silica Chromium removal Reduction–sorption Water purification a b s t r a c t Organically-modified silica gels bearing mercaptopropyl and ethylenediaminetriacetate groups (SiO 2 –SH/ED3A) have been used for reduction and subsequent sequestration of Cr(VI) species. The uptake mechanism involves Cr(VI) reduction by thiol groups (SH) and further immobilization of the so-generated Cr(III) species via complexation to the ethylenediaminetriacetate moieties (ED3A). The most appropri- ate pH range (1–3) for complete Cr(VI) reduction–sorption by SiO 2 –SH/ED3A originates from the balance between full reduction of Cr(VI) by SH, requiring low pH values, and quantitative complexation of Cr(III) by ED3A, which is favored in less acidic media. Such bi-functional adsorbents are considerably more effective at removal of Cr(VI) than those simply modified with thiol groups alone. The whole reduction–sorption process was characterized by fast kinetics, thus permitting efficient use of the SiO 2 –SH/ED3A adsorbent in dynamic conditions (column experiments). Monitoring the amount of immobilized chromium species on the solid was achieved using X-ray fluorescence spectroscopy and UV–vis spectroscopy. Studying the influence of ionic strength and presence of heavy metals revealed few interference on Cr(VI) removal. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Chromium is widely used in diverse industrial processes, includ- ing alloys and steel manufacturing, metal finishing, electroplating, leather tanning, cooling tower blowdown, or pigments synthesis and dyeing [1–3]. In spite of considerable reduction of industrial disposal of chromium observed today, chromium contamination of soil and groundwater remains a significant environmental problem [2,4,5], and there still exists a need to control the occu- pational exposure and emission limit values of anthropogenic chromium as well as to find appropriate treatments likely to lower chromium pollution. Considering the difference in biological activ- ity of the various forms of chromium, the present-day regulations and quality guidelines call for distinction between Cr(VI) and Cr(III) ∗ Corresponding author. Tel.: +33 (3) 83685243; fax: +33 (3) 83275444. E-mail addresses: alain.walcarius@univ-lorraine.fr, alain.walcarius@lcpme.cnrs-nancy.fr (A. Walcarius). species, the former being considered as more toxic than the latter [4,6–8]. Several well-documented reviews or monographs are available dealing with chromium removal from wastewaters [9–16]. It came out that firstly proposed remediation schemes were directed to reduce the carcinogenic, soluble, and mobile Cr(VI) (i.e., in acidic medium, pH ∼2) to the less toxic and less mobile Cr(III), which forms insoluble or sparingly soluble precipitates (i.e., in alkaline medium, above pH ∼9–10). Such methods are only applicable for concentrated industrial wastewater and produce large amounts of chemical sludge [17], generating thereby the search for other approaches. Nowadays existing technologies (see details in Sup- plementary Data) are mainly based on immobilization on solid supports, or separation and filtration processes, associated or not to reduction/precipitation. All these methods exhibit advantages and disadvantages and are most often applied to the removal of chromium from solutions containing relatively high initial chromium concentrations (i.e., >100 mg L -1 ). Adsorption, though likely to generate non negligible amounts of sludge with associated disposal problems, merged recently among the most promising 0304-3894/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jhazmat.2013.02.019