jesc.ac.cn Journal of Environmental Sciences 2011, 23(2) 288–293 Mechanism of Cd(II) adsorption by macrofungus Pleurotus platypus R. Vimala, Nilanjana Das * School of Biosciences and Technology, VIT University, Vellore 632014, Tamil Nadu, India. E-mail: vimararagu@yahoo.co.in Received 07 February 2010; revised 31 March 2010; accepted 15 April 2010 Abstract The mechanism of Cd(II) uptake by the dead biomass of macrofungus Pleurotus platypus was investigated using different chemical and instrumental techniques. Sequential removal of cell wall components of the biosorbent revealed that structural polysaccharides play a predominant role in the biosorption of Cd(II). The adsorption kinetics fitted well with the pseudo second-order model suggested that the adsorption of Cd(II) on P. platypus involved a chemisorption process. Transmission electron microscopy of the cadmium exposed biomass confirmed the deposition of the metal mainly in the cell wall. Fourier transform infrared spectroscopic analysis of the metal loaded biosorbent confirmed the participation of –OH, –NH and C–O–C groups in the uptake of Cd(II). Energy dispersive X-ray analysis of the biosorbent before and after metal uptake revealed that the main mechanism of adsorption was ion-exchange. The effectiveness of CaCl 2 in the desorption of cadmium perhaps suggested the exchange of Ca 2+ with Cd(II). Key words: biosorption; mechanism; ion-exchange; Pleurotus platypus; macrofungus; cadmium DOI: 10.1016/S1001-0742(10)60405-6 Citation: Vimala R, Das N, 2011. Mechanism of Cd(II) adsorption by macrofungus Pleurotus platypus. Journal of Environmental Sciences, 23(2): 288–293 Introduction Cadmium receives wide attention by environmentalists as one of the most toxic heavy metals. The increasing presence of cadmium in the environment is mainly due to its use in electroplating, paint pigments, plastics, alloy preparation, mining, ceramics and silver-cadmium batter- ies (Volesky, 1990; Wase and Forster, 1997). Cadmium toxicity may be observed by a variety of syndromes and effects including renal dysfunction, hypertension, hepatic injury, lung damage and teratogenic effects (Yu et al., 1999; Kaewsarn and Yu, 2001; Lodeiro et al., 2006). Because of the toxicity and bioaccumulation, Cd(II) is considered as a priority pollutant by the US Environmental Protection Agency. The permissible limit for Cd(II) as described by World Health Organization is 0.01 mg/L. The usual methods for removal of heavy metal ions from aque- ous solutions are chemical precipitation, ion exchange, solvent extraction, phytoextraction, ultrafiltration, reverse osmosis, electrodialysis, and adsorption (Patterson, 1985; Bhattacharya et al., 2006). However, technical or economic factors limit the feasibility of such processes. Most of these methods suffer from some drawbacks, such as high capital and operational cost or the disposal of the residual metal sludge, and are not suitable for small-scale industries (Kobya et al., 2005). Biosorption which utilizes biological materials as adsor- * Corresponding author. E-mail: nilanjana00@lycos.com bents is an emerging technology for the removal of heavy metals from industrial wastewater. The main advantages of this technique are the reusability of biomaterial, low operating cost, improved selectivity for specific metals of interest, removal of heavy metals from effluent irrespective of toxicity, short operation time, and no production of secondary compounds which might be toxic (Mungasavalli et al., 2007). It employs a wide variety of biomasses, such as fungi, algae and bacteria, for removal of metal ions (Sag and Kutsal, 2000; Gupta et al., 2001; Nourbakhsh, 2002). Although several proprietary biosorption processes such as AlgaSORB TM (Brierley et al., 1986) and AMT- Bioclaim TM (Darnall, 1991) have been developed and commercialized, a lack of understanding of the mecha- nism underlying the metal-sorption process has hindered adequate assessment of process performance and thus the expected widespread application of biosorption. Encourag- ing results from our previous study (Vimala and Das, 2009) has stimulated interest in understanding the mechanism of Cd(II) uptake by the macrofungus Pleurotus platypus. As far as the authors are aware, there are scanty reports in the literature on the mechanism of Cd(II) biosorption by macrofungi. Therefore, the real challenge for the field of biosorption will be to identify the actual mechanism of metal uptake by the biosorbents. Elucidation of metal uptake mechanism may provide a useful basis for manipu- lation and improvement of the biosorbent selectivity for the desired metal (Kuyucak and Volesky, 1989). The objective