Long-term efficiency and kinetic evaluation of ZVI barriers during clean-up of copper containing solutions K. Komnitsas a, * , G. Bartzas b , K. Fytas c , I. Paspaliaris b a Department of Mineral Resources Engineering, Technical University of Crete, 73 100 Chania, Greece b Laboratory of Metallurgy, School of Mining and Metallurgical Engineering, National Technical University of Athens, Zografos Campus, 157 80 Athens, Greece c Department of Mining, Metallurgical and Materials Engineering, Laval University, Quebec City, PQ, Canada Received 23 February 2007; accepted 14 May 2007 Available online 29 June 2007 Abstract Sixteen continuous column experiments were carried out under dynamic flow conditions in order to study the efficiency of zero-valent iron (ZVI) permeable reactive barriers (PRBs) to remove copper from solutions. The effect of various operational parameters, such as pH of the feed solution (2.5 and 4.5), initial copper concentration (5 and 50 mg/L), pore water velocity (30.48 and 152.40 cm/day) and res- idence time on iron corrosion and degree of copper removal was evaluated. Breakthrough curves showed that higher initial copper con- centration and pore water velocity accelerated iron corrosion and slowed down the rate of copper removal due to the formation of mineral precipitates. The maximum removal rates recorded for initial copper concentrations of 5 and 50 mg/L were 2.68 and 13.33 mg/g of ZVI/sand mixture, after 440 and 227 pore volumes, respectively. The reduction of copper follows a pseudo-first-order kinetics while the rate constants (k obs ) decrease over time from 0.60 to 0.10 h 1 , indicating thus progressive passivation of the ZVI/sand reactive bed. Mineralogical studies of the exhausted reactive mixture, using XRD and SEM/EDX, confirmed the deposition of copper on the ZVI surface and the formation of iron (oxy)hydroxides. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Environmental; Reaction kinetics; Modelling 1. Introduction Copper is a well-known contaminant due to its toxicity in aquatic environments. Elevated levels of copper may cause health implications such as liver and kidney failure or Wilson’s disease (Rengaraj et al., 2004). Copper derives from several sources including power stations, electroplat- ing, combustion, mining and smelting activities. Thus, the clean-up of copper-containing discharges is necessary in order to prevent contamination of surface and groundwater. Recently, attention has been paid to the use of perme- able reactive barriers (PRBs) for the cleanup of acidic plumes and the prevention of groundwater contamination (Wilkin and McNeil, 2003; Kanel and Choi, 2007). PRBs are defined as ‘‘an emplacement of reactive materials in the subsurface designed to intercept a contaminant plume, provide a preferential flow path through the reactive media and transform the contaminant(s) into environmentally acceptable forms to attain remediation concentration goals at points of compliance’’ (U.S.EPA, 1998; Gavaskar et al., 1998). PRBs containing zero-valent iron (ZVI) have been used to remove redox-sensitive inorganic contaminants such as hexavalent chromium (Wilkin et al., 2005), ura- nium (Noubactep et al., 2005) and metalloids such as arsenic (Bang et al., 2005) from leachates. The proposed clean-up mechanisms involve formation of complexes with nascent iron oxides, sorption onto aged corrosion prod- ucts, reductive precipitation and electrochemical reduction 0892-6875/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.mineng.2007.05.002 * Corresponding author. E-mail address: komni@mred.tuc.gr (K. Komnitsas). This article is also available online at: www.elsevier.com/locate/mineng Minerals Engineering 20 (2007) 1200–1209