Research article Immobilization in cement mortar of chromium removed from water using titania nanoparticles Ahmed Husnain, Ishtiaq Ahmed Qazi, Wasim Khaliq * , Muhammad Arshad National University of Sciences and Technology (NUST), Islamabad, Pakistan article info Article history: Received 6 December 2015 Received in revised form 14 February 2016 Accepted 16 February 2016 Available online xxx Keywords: Adsorption Toxic chromium Titania nanoparticles Mortar Compressive strength Chromium leachate abstract Because of the high toxicity of chromium, particularly as Cr (VI), it is removed from industrial effluents before their discharge into water bodies by a variety of techniques, including adsorption. Ultimate disposal of the sludge or the adsorbate, however, is a serious problem. While titania, in nanoparticle form, serves as a very good adsorbent for chromium, as an additive, it also helps to increase the compressive strength of mortar and concrete. Combining these two properties of the material, titania nanoparticles were used to adsorb chromium and then added to mortar up to a concentration of 20% by weight. The compressive strength of the resulting mortar specimens that replaced 15% of cement with chromium laden titania showed an improved strength than that without titania, thus confirming that this material had positive effect on the mortar strength. Leachate tests using the Toxicity Characteristics Leaching Procedure (TCLP) confirmed that the mortar sample chromium leachate was well within the permissible limits. The proposed technique thus offers a safe and viable method for the ultimate disposal of toxic metal wastes, in general, and those laden waste chromium, in particular. © 2016 Elsevier Ltd. All rights reserved. 1. Introduction Chromium a naturally occurring element found in rocks, soil, animals, plants and volcanic dust and gases, is one of the most abundant element in the Earth's crust. It exists in oxidation states ranging from IV to þVI inclusively, with the most stable forms being trivalent (III) chromium and hexavalent (VI) chromium (Becquer et al., 2003). In nature Cr is chiefly found in the trivalent form (Kota s and Stasicka, 2000) while Cr (VI) in the environment is almost totally derived from human activities (Schneider et al., 2012). Whereas, the metallurgical, chemical, and refractory in- dustries are the fundamental users of chromium (Dayan and Paine, 2001), leather tanning and chrome plating processes are the major sources of chromium pollution (Sharma et al., 2012). Chromium in the hexavalent oxidation state, Cr (VI) is of grave concern because of its toxicity, high solubility, and mobility in water (Rashid et al., 2011) makes it 500 times more toxic than the Cr (III) and it has been recognized as a pulmonary carcinogenic along with causing other health effects such as respiratory, skin, carcinogenic, renal, hepatic, haematological problems while being genotoxic and mutagenic (Saha et al., 2011). Cr (VI) is carcinogenic to rats and mice after chronic oral exposure (Stout et al., 2009). Penetration of Cr (VI) in skin will cause painless erosive ulceration “chrome holes” with delayed healing and increased stomach and lung cancer risks in humans due to Cr (VI) exposure has also been reported (Beaumont et al., 2008). Toxic effects of accumulated Cr on plant growth and development include alteration in the germina- tion process and effect on the growth of roots, stems and leaves has also been observed (Shanker et al., 2005). Methodologies have been developed in removing chromium from industrial wastewater by chemical precipitation, ion ex- change, electrochemical treatment, membrane filtration, flotation, coagulation flocculation and adsorption (Barakat, 2011). Although, precipitation method is used for its simplicity process and is inexpensive but, it is ineffective when metal ion concentration is low and can produce large amount of sludge which needs to be treated with great difficulties (Fu and Wang, 2011). Thus, adsorp- tion is considered as one of the most suitable chromium removal methods due to its cost effectiveness, higher efficiency, and ease of operation (Djellabi and Ghorab, 2015) and the availability of a wide range of adsorbents like silica composites (Kumar et al., 2007), activated carbon (Sekhar et al., 2012), fly ash (Veni and Ravindhranath, 2012) and microbes (Liu et al., 2013). Further, various low cost adsorbents (Bailey et al., 1999) and microbial * Corresponding author. NUST Institute of Civil Engineering (NICE), School of Civil and Environmental Engineering, NUST Campus, Sector H-12, Islamabad, Pakistan.. E-mail address: wasimkhlaiq@nice.nust.edu.pk (W. Khaliq). Contents lists available at ScienceDirect Journal of Environmental Management journal homepage: www.elsevier.com/locate/jenvman http://dx.doi.org/10.1016/j.jenvman.2016.02.026 0301-4797/© 2016 Elsevier Ltd. All rights reserved. Journal of Environmental Management 172 (2016) 10e17