artículo chemosphere.pdf

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Technical Note Oxidation of Orange G by persulfate activated by Fe(II), Fe(III) and zero valent iron (ZVI) S. Rodrig uez , L. Vasquez, D. Costa, A. Romero, A. Santos Dpt. Ingenieria Química, Facultad Químicas, Universidad Complutense, 28040 Madrid, Spain h i g h l i g h t s Oxidation of Orange G (azo dye) with iron activated persulfate was studied.  An oxidation pathway was proposed for OG oxidation by activated persulfate.  The inuence of iron valence (0, II and III) on the activity was studied.  Product distribution, mineralization and detoxication were also studied. a r t i c l e i n f o  Article history: Received 30 July 2013 Received in revised form 11 December 2013 Accepted 12 December 2013 Available online 16 January 2014 Keywords: Dye Orange G Persulfate Oxidation pathway Iron valence Ecotoxicity a b s t r a c t Persulfate (PS) was employed in the oxidation of Orange G (OG), an azo dye commonly found in textile wastewaters. Activation of PS was conducted with iron to generate sulfate free radicals (SO 4  ) with high redox potential capable to oxidize most of the organics in water. Identication of oxidation intermediates was carried out by analyzing at different times organic by-products generated from treatment of a con- centrate dye solution (11.6 mM) with 153 mM of PS and 20 mM of Fe(II) at 20  C. Intermediate reaction products (mainly phenol (PH) and benzoquinone (BQ), and in less extent aniline, phenolic compounds and naphthalene type compounds with quinone groups) were identied by GC/MS and HPLC, and an oxi- dation pathway was proposed for the oxidation of OG with iron activated PS. The effect of iron valence (0, II and III) in the oxidation of an aqueous solution of OG (containi ng 0.1 mM) was studied in a 0.5 L batch reactor at 20 C. Initial activator and PS conce ntrati ons employed were both 1 mM. Compl ete pollutant removal was achieved within the rst 30 min when iron II or III were employed as activators. Quinone intermediates generated during pollutant oxidation may act as electron shuttles, allowing the reduction of Fe(III) into Fe(II) in the redox cycling of iron. Therefore, activation of PS by Fe(III) allowed complete OG removal. When zero valent iron (ZVI) was employed (particle diameter size 0.74 mm) the limiting step in SO 4  generation was the surface reaction between ZVI and the oxidant yielding a lower oxidation rate of the dye. An increase in the oxidant dosage (0.2 mM OG, 2 mM Fe(III) and 6 mM PS) allowed complete pollutant and ecotoxicity removal, as well as mineralization close to 75%.  2013 Elsevier Ltd. All rights reserved. 1. Introduction Textile industries generate considerable amounts of wastewa- ters pollut ed with dyes (over 1 Mt of diff eren t dyes produc ed annually in the world ( Peng et al., 2008). Among them, azo dyes (with a chromophore group  AN@NA) can be considered one of the most important commer cial dyes as they repre sent around 60% of the world market for dyes used by the textile industries (Kunz et al., 2002; Azam and Hamid, 2006 ). However, their poten- tial disadvantages from an environmental point of view such as toxicity, non-biodegradation and carcinogenic potential must be taken into account ( Chen et al., 2003; Peng et al., 2008 ). Therefore, the removal of these kinds of pollutants is of great interest, since conventional biological treatment technologies are not able to do it efciently. Seve ral adva nced oxid atio n proc esses, empl oyin g Fent on ´ s Reag ent (Fer nan dez et al., 1999; Xu et al. , 2004; Hsueh et al., 2005), TiO 2  mediated photocatalysis (Vinodgopal et al., 1996; Xie and Li, 2006; Yu et al., 2008 ), potassium permanganate (Xu et al., 2005; Aleboyeh et al., 2009 ) and oxone/Co 2+ reagent (Fernandez et al., 2004), have been examined for the degradation of dyes. Re- cently, PS (S 2 O 2 8  ), a strong two-electron oxidiz ing agent with a re- dox potential of 2.01 V, has proved to be efcient in textile dyes removal (Kusic et al., 2011). Moreover, PS is typically activated to generate reactive SO 4  (Liang et al., 2004a; Rodriguez et al., 2012 ) with oxidation–reduction potential of 2.6 V ( Berlin, 1986), which can oxidize most of the organics in water. Besides of the high redox 0045-6535/$ - see front matter   2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.chemosphere.2013.12.037 Corresponding author. Tel.: +34 913944173. E-mail address:  [email protected] (S. Rodriguez). Chemosphere 101 (2014) 86–92 Contents lists available at  ScienceDirect Chemosphere journal homepage:  www.elsevier.com/locate/chemosphere

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