Biosorption of heavy metals from aqueous solutions with tobacco dust B.C. Qi, C. Aldrich * Department of Chemical Engineering, University of Stellenbosch, Stellenbosch, Private Bag X1, Matieland 7602, South Africa Received 21 November 2006; received in revised form 19 October 2007; accepted 24 October 2007 Available online 21 December 2007 Abstract A typical lignocellulosic agricultural residue, namely tobacco dust, was investigated for its heavy metal binding efficiency. The tobacco dust exhibited a strong capacity for heavy metals, such as Pb(II), Cu(II), Cd(II), Zn(II) and Ni(II), with respective equilibrium loadings of 39.6, 36.0, 29.6, 25.1 and 24.5 mg of metal per g of sorbent. Moreover, the heavy metals loaded onto the biosorbent could be released easily with a dilute HCl solution. Zeta potential and surface acidity measurements showed that the tobacco dust was negatively charged over a wide pH range (pH > 2), with a strong surface acidity and a high OH  adsorption capacity. Changes in the surface morphology of the tobacco dust as visualized by atomic force microscopy suggested that the sorption of heavy metal ions on the tobacco could be asso- ciated with changes in the surface properties of the dust particles. These surface changes appeared to have resulted from a loss of some of the structures on the surface of the particles, owing to leaching in the acid metal ion solution. However, Fourier transform infrared spec- troscopy (FTIR) showed no substantial change in the chemical structure of the tobacco dust subjected to biosorption. The heavy metal uptake by the tobacco dust may be interpreted as metal–H ion exchange or metal ion surface complexation adsorption or both. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Biosorption; Heavy metals; Lignocellulose; Tobacco 1. Introduction The increased attention on the harmful effects of heavy metal ions on human health and the environment over the past few decades has led to a concomitant focus on improved water quality. Since industrial effluents in partic- ular are a major contributor to heavy metal contamination, the removal of such metals from these effluents has been a priority in the tightening and enforcement of environmen- tal regulations. Removal of these contaminants can be accomplished by use of physical or chemical methods, including the use of chemical reagents, ion exchange, acti- vated carbon sorption and membrane technology. Most of these approaches have significant disadvantages. For example, chemical reagents are costly (Kadiverlu et al., 2001), as the active agents cannot be recovered for use in successive treatment cycles. Moreover, the end product is usually a low volume, highly concentrated metalliferous sludge that may be difficult to dewater and dispose of (San- dau et al., 1996). Likewise, ion exchange and membrane systems could be expensive, especially in small-scale pro- cesses, with the resins or membranes prone to fouling or oxidation. Similarly, activated carbon, the most widely used adsorbent in the treatment of waste water, is expen- sive and may also require complexing agents to improve its ability to remove inorganic matter (Babel and Kurnia- wan, 2002). Biosorption, which is the ability of certain biomaterials to bind and concentrate heavy metals from even the most dilute aqueous solutions, offers a technically feasible and economically attractive alternative to the conventional technologies for removal of heavy metal from the contam- inated effluents (Davis et al., 2000; De Carvalho et al., 2001; Esposito et al., 2001; Demir and Arisoy, 2007). Various biomaterials produced or harvested from natural resources or agricultural products, mostly in metabolically 0960-8524/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2007.10.042 * Corresponding author. Tel.: +27 21 808 4485; fax: +27 21 808 2059. E-mail address: CA1@sun.ac.za (C. Aldrich). Available online at www.sciencedirect.com Bioresource Technology 99 (2008) 5595–5601