Adsorption of hexavalent chromium from aqueous solution by modified corn stalk: A fixed-bed column study Suhong Chen, Qinyan Yue ⇑ , Baoyu Gao, Qian Li, Xing Xu, Kaifang Fu Shandong Key Laboratory of Water Pollution Control and Resource Reuse, School of Environmental Science and Engineering, Shandong University, Jinan 250100, China article info Article history: Available online 3 December 2011 Keywords: Corn stalk Hexavalent chromium Adsorption Fixed-bed column abstract Continuous fixed-bed column studies were carried out by using modified corn stalk (MCS) as an adsor- bent for the removal of Cr(VI) from aqueous solution. The effect of various parameters like bed depths (1.4, 2.2 and 2.9 cm), flow rate (5, 10 and 15 mL/min), influent Cr(VI) concentrations (100, 200 and 300 mg/L) and influent solution pH (2.66, 4.91 and 5.66) was investigated. The exhaustion time increased with increase of bed depth, decrease of flow rate and influent concentration. The Adams–Bohart, Thomas and Yoon–Nelson models were applied to the adsorption under varying experimental conditions to pre- dict the breakthrough curves and to evaluate the model parameters of the fixed-bed column that are use- ful for process design. The Thomas and Yoon–Nelson models were in good agreement with the experimental data. The MCS column study states the value of the excellent adsorption capacity for the removal of Cr(VI) from aqueous solution. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Hexavalent chromium [Cr(VI)] is considered as a major pollu- tant in water pollution and there has been a great increase and accumulation in environment due to the rapid industrialization over the years (Gupta and Babu, 2009a; Kumar and Chakraborty, 2009). Chromium exists in nature in three oxidation states for Cr(II), Cr(III) and Cr(VI), only the latter two of which are stable (Aydın and Aksoy, 2009; Mohan and Pittman, 2006; Sarin and Pant, 2006). Cr(VI) is primarily in the form of chromate ðCrO 4 2 Þ and dichromate ðCrO 7 2 Þ ions is known to be highly mobile, and much more toxic and hazardous than Cr(III) (Malkoc et al., 2006). Chro- mium waste is generated from various industrial processes, such as electroplating, steel fabrication, leather tanning, wood preserva- tions, textile dyeing, paint, and pigments, and petroleum refining processes (Kumar and Chakraborty, 2009; Gupta et al., 2010). The permissible levels of Cr(VI) in potable water, inland surface water and industrial wastewater by WHO (world health organization) are 0.05, 0.1 and 0.25 mg/L, respectively (Aydın and Aksoy, 2009). Therefore, it is necessary to eliminate Cr(VI) from the envi- ronment, and it is also essential that the effluents should be treated before discharging Cr(VI) into aquatic environments. Various physicochemical methods have been developed for re- moval of Cr(VI), including chemical precipitation, electrochemical pre- cipitation, oxidation/reduction, ion exchange, membrane separation, ultrafiltration, flotation, solvent extraction, evaporation, reverse osmo- sis, foam separation, dialysis/electrodialysis, adsorption, biosorption (Gupta and Babu, 2009a; Kumar and Chakraborty, 2009; Aydın and Ak- soy, 2009; Mohan and Pittman, 2006; Sarin and Pant, 2006; Malkoc et al., 2006; Gupta et al., 2010; Pehlivan and Cetin, 2009), etc. Among them, the most commonly used methods are adsorption, reduction, precipitation and ion exchange. However, these techniques, except for ion exchange, have considerable disadvantages, such as incomplete metal removal, expensive equipment and monitoring system, high re- agent and energy requirements, or generation of toxic sludge or waste that requires proper disposal (Pehlivan and Cetin, 2009). In recent years, synthetic ion exchanger is increasingly considered as a simple, effective and inexpensive alternative. Anion exchange resins are gener- ally used to remove metal ions from wastewater. Agricultural by-products are abundant, low-cost, underutilized lingocellulosic materials which show poor ion exchange proper- ties. Therefore, through the introduction of quaternary ammonium groups, their anion exchange capacity can be enhanced (Wartelle and Marshall, 2005). Corn stalk (CS) is also an abundant agricul- tural waste and has a high content of cellulose, which is a large, lin- ear-chain polymer with a large number of hydroxyl groups (Zheng et al., 2010). However, to the best of our knowledge, there has been little research on the use of CS, and the majority of studies mainly focused on the Cr(VI) adsorption capacity in batch experiments. Moreover, in practical industrial water treatment processes, adsorption in fixed-bed columns are preferable, and the experi- mental data obtained from the laboratory scale fixed-bed columns are helpful for industrial application (Baral et al., 2009; Calero et al., 2009). In our previous research, CS was used as an adsorbent for the removal of Cr(VI) ions in batch experiments (Chen et al., 2011b). 0960-8524/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2011.11.110 ⇑ Corresponding author. Tel.: +86 531 88365258; fax: +86 531 88364513. E-mail address: qyyue@sdu.edu.cn (Q. Yue). Bioresource Technology 113 (2012) 114–120 Contents lists available at SciVerse ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech