Journal of Hazardous Materials B137 (2006) 1149–1155 Adsorption of copper and lead in aqueous solution onto bentonite modified by 4 ′ -methylbenzo-15-crown-5 Liu Yun, Shen Xing, Xian Qiming, Chen Haidong, Zou Huixian ∗ , Gao Shixiang State Key Laboratory of Pollution Control and Resource Reuse, School of Environment, 22 Hankou Road, Nanjing University, Nanjing 210093, China Received 22 December 2005; received in revised form 26 March 2006; accepted 27 March 2006 Available online 7 April 2006 Abstract The adsorption of heavy metal ions (Cu 2+ and Pb 2+ ) onto organobentonite modified by 4 ′ -methylbenzo-15-crown-5 (MB15C5) from bentonite compared with natural bentonite (N-Bentonite) is described in this paper. The kinetic parameters of the models are calculated and discussed, and closely fitted a pseudo-second-order model in all cases. For bentonite modified with MB15C5 (MB15C5-Bentonite) and N-Bentonite, the equilibrium data closely fitted the Langmuir model and showed the following affinity order: Pb 2+ > Cu 2+ , and the adsorption capacity of MB15C5- Bentonite is higher than that of N-Bentonite for Pb 2+ and Cu 2+ . The effect of pH is examined over the range 1.5–6. The adsorption of Cu 2+ and Pb 2+ increases with increasing pH and the adsorption of Cu 2+ and Pb 2+ reaches a maximum at pH 3.5–6. © 2006 Elsevier B.V. All rights reserved. Keywords: 4 ′ -Methylbenzo-15-crown-5; Adsorption; Bentonite; Heavy metal 1. Introduction Toxic metals at trace levels contamination of soil and poten- tial fouling of groundwater is a complex and common problem, and it is well known that heavy metal pollution is a serious threat to the environment. Pb, Cd, Cu, Hg, Cr, Ni and Zn are the main trace elements that are of greatest concern. In order to prevent contamination of subsoil, groundwater and surface water by these elements, there has recently been a grow- ing interest in the development of materials capable of adsorbing heavy metals [1–3]. Effective adsorbents with a strong affinity and, subsequently, a high loading capacity for targeted metal ions have been prepared by modifying the surface of various substrates, such as silica gel [4], aerobic granules [5,6], zeolite [7] and clay [8,9], with heavy metal complexing agents (e.g., surfactant [10] and thiols [11,12]). Because of high specific surface areas, low cost and ubiq- uitous presence in most soils, clay is usually chosen to prevent heavy metals being released into the environment [13]. One such clay is bentonite, which is a 2:1 type of clay, and its unit layer ∗ Corresponding author. Tel.: +86 25 83596823; fax: +86 25 83707304. E-mail address: hxzou@nju.edu.cn (H. Zou). structure consists of one Al 3+ octahedral sheet placed between two Si 4+ tetrahedral sheets. The isomorphous substitution of Al 3+ for Si 4+ in the tetrahedral layer and Mg 2+ or Zn 2+ for Al 3+ in the octahedral layer results in a net negative surface charge on the clay [14]. This charge imbalance is offset by exchangeable cations (e.g. H + , Na + and Ca 2+ ) at the clay sur- face. The most important factors regulating heavy metals in clay include the type of clay, the metal involved, its concentration and pH [15,16]. Many research studies have focused on clay and clay constituents, such as clay minerals, metal (hydr)oxides and organic matter [17–21]. Crown ether is known to complex with numerous metals [22]. Bruening and co-workers [23] and Izatt et al. [24] used silica gel modified by crown ether to remove metal cations from organic solvents and aqueous solution. Crown ether modified bentonite was first reported in 1978 by Ruiz-Hitzky and Casal [25]. They pointed out that crown ethers could be intercalated between the layers of 2:1 bentonite saturated with alkaline or alkaline-earth cations. They also found that crown ether modified bentonite was very stable. Sivaiah et al. has studied adsorption of cesium and strontium to dicyclohexano-18-crown-6 modified bentonite [26]. However, few research studies have focused on the inter- actions of heavy metal with the surface of bentonite modified by 4 ′ -methylbenzo-15-crown-5 (MB15C5). 0304-3894/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2006.03.057