Chemical Engineering Journal 168 (2011) 909–917 Contents lists available at ScienceDirect Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej Removal of Cr(VI) from aqueous solution using modified corn stalks: Characteristic, equilibrium, kinetic and thermodynamic study Suhong Chen, Qinyan Yue ∗ , Baoyu Gao, Qian Li, Xing Xu Shandong Key Laboratory of Water Pollution Control and Resource Reuse, School of Environmental Science and Engineering, Shandong University, No. 27 Shanda South Road, Jinan, Shandong 250100, China article info Article history: Received 11 October 2010 Received in revised form 17 January 2011 Accepted 17 January 2011 Keywords: Modified corn stalks Adsorption Kinetics Isotherms Thermodynamics abstract The adsorbent modified from corn stalks was synthesized after the reaction between epichlorohydrin and triethylamine by using diethylenetriamine (DETA) as modifying agent in the presence of N,N- dimethylformamide (DMF). The performance of the modified corn stalks (MCS) was characterized by BET, SEM, zeta potential, FTIR and thermogravimetric analysis. The adsorption of Cr(VI) from aqueous solutions with MCS which contained amine groups was studied at varying adsorbent dose, initial Cr(VI) concentration, pH, contact time and temperature. Results showed that the Cr(VI) adsorption depended insignificantly on pH but significantly on temperature. The batch equilibrium data fitted well to the Langmuir isotherm. Maximum adsorption capacity of MCS for Cr(VI) was 200.00 mg/g at 303 K which was relatively large compared to some adsorbents as reported. Kinetic data were best fitted with the pseudo-second-order kinetic model. The intra-particle diffusion model was applied to investigate the adsorption mechanisms. The obtained thermodynamic parameters showed that the adsorption of Cr(VI) onto the adsorbent was an spontaneous and endothermic process. These results showed that the anion exchanger could be considered as a potential adsorbent for the removal of Cr(VI) ions from aqueous solutions. © 2011 Elsevier B.V. All rights reserved. 1. Introduction There is growing attention to the health risks on humans and animals due to the existence of heavy metals in the environment. The accumulation of which in living tissues throughout the food chain poses a serious health problem [1]. Even though some of these heavy metal ions in traces play a significant role in human metabolic system, their higher concentrations are toxic which can cause severe physiological or neurological damage. Among the various heavy metals, chromium (Cr) is one of the most toxic pollu- tants generated by the electroplating, fungicides, leather tanning, metal finishing, steel fabrication, textile industries and chromate preparation. Cr in nature exists in two most common and sta- ble oxidation states, trivalent chromium [Cr(III)] and hexavalent chromium [Cr(VI)]. Cr(VI) is more hazardous than Cr(III) as it can diffuse as CrO 4 2- or HCrO 4 - through cell membranes and oxidize biological molecules [2], and has been reported as one of the top-priority toxic pollutants defined by the US Environ- mental Protection Agency (EPA), and the Chinese Environmental Protection Board (EPB) [1,3]. The maximum permissible limits of Cr(VI) for discharge into potable water, inland surface water and ∗ Corresponding author. Tel.: +86 531 88365258; fax: +86 531 88364513. E-mail addresses: qyyue@sdu.edu.cn, qyyue58@yahoo.com.cn (Q. Yue). industrial wastewater are 0.05, 0.1 and 0.25 mg/L, respectively [4]. To comply with the stringent discharge limits, it is deemed necessary that industries treat their final effluents in order to reduce the Cr(VI) ions concentration in wastewater to the accept- able levels before discharge into the municipal sewers. Treatment technologies applied for removing Cr(VI) from wastewater include adsorption, biosorption, coprecipitation, electrodialysis, chemical precipitation, electrochemical precipitation, membrane filtration, solvent extraction, reverse osmosis and ion exchange [1,3,5]. Although activated carbon, as the classical inorganic adsorbent, is currently the best known and most efficient adsorbent owing its high specific surface area, while its high cost and expensive regen- eration cost restrict its comprehensive use [6]. Cr(VI) is present in the form of anions species in the aqueous solutions, thus, to remove these toxic metal ions from water, the adsorbent must have the anion exchange properties [7]. Agricultural by-products are abundant, low-cost, underutilized lingocellulosic materials that are normally poor anion exchange resins; however, through the introduction of quaternary ammo- nium groups, their anion exchange capacity can be enhanced [8]. The lignocellulosic materials mainly constitute of cellulose, hemi- celluloses, lignin and extractive matters [9]. Corn stalks (CS), rich in natural cellulose, are most abundant in agricultural residues, but most of them are disposed of by direct burning in the field 1385-8947/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.cej.2011.01.063