Biosorption of cadmium metal ion from simulated wastewaters using Hypnea valentiae biomass: A kinetic and thermodynamic study Aravindhan Rathinam, Bhaswant Maharshi, Sreeram Kalarical Janardhanan, Raghava Rao Jonnalagadda * , Balachandran Unni Nair Chemical Laboratory, Central Leather Research Institute, Sardar Patel Road, Adyar, Chennai, India article info Article history: Received 7 April 2009 Received in revised form 4 August 2009 Accepted 4 August 2009 Available online 26 August 2009 Keywords: Biosorption Cadmium Hypnea valentia Kinetics Thermodynamics abstract Present study deals with the evaluation of biosorptive removal of cadmium by red macro alga Hypnea val- entiae. Experiments have been carried out to find the effect of various parameters such as initial cadmium concentration, experimental pH and temperature on the biosorption potential of H. valentiae. Optimum pH for biosorption of cadmium was found to be 6 ± 0.3. A maximum removal of about 17 mg of cadmium per g of micro algae was observed at pH 6.0 for 250 mg L 1 solution of cadmium. Kinetics of cadmium biosorption by H. valentiae biomass is better described by pseudo first order kinetic model. The equilib- rium isotherm data are very well represented by Langmuir isotherm equation, which confirmed the monolayer coverage of cadmium onto H. valentiae biomass. Various thermodynamic parameters such as change in enthalpy, free energy and entropy were estimated. It was also clearly observed that the pres- ence of neutral salts and other metal ions affected the cadmium uptake behavior of the biomass considerably. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Cadmium is among the heavy metals, which is regarded as an element of high toxicity. The cadmium exposure leads to adverse health effects to human viz. renal dysfunction, liver damage, bone degradation and hypertension (Nordberg et al., 1993). Due to this cadmium has been included in red list of priority pollutants by Department of Environment, UK (UK Red List Substances, 1991) and in List I (the ‘‘black list”) of Directive 76/464/EEC (Council direc- tive, 1976). USEPA has also classified cadmium as group B1 carcin- ogen (USEPA, 1999). The most commonly employed methodologies for the treatment of cadmium containing wastewaters include chemical precipitation, evaporation, ion exchange and membrane separation. Although the effectiveness of these methods has been proved, they suffer from a major disadvantage, namely lack of cost effectiveness. Other limitations include energy intensive process- ing, low efficiency, not feasible to reduce the cadmium concentra- tion to levels as low as required by environmental legislation and production of toxic chemical sludge, which needs additional treat- ment. Therefore there is a need for the development of economical, effective and safe methods for removal of cadmium. Biosorption is relatively a new treatment methodology for removing heavy metal ions from dilute solutions. Biosorption has received considerable attention owing to be an efficient, clean and cheap technology for treatment of wastewater. Lot of research has been carried out for developing and employing inexpensive biosorbents for the treatment of wastewaters containing heavy metals (Pollard et al., 1992; McHale and McHale, 1994; Kapoor and Viraraghavan, 1995; Veglio’ and Beolchini, 1997; Bailey et al., 1999; Babel and Kurniawan, 2003; Wang and Chen, 2006; Demirbas, 2008; Sud et al., 2008; Vijayaraghavan and Yun, 2008). Of the many types of biosorbents used by several investigators, seaweed has proved to be the most efficient biomass for the re- moval of heavy metal ions from wastewaters. Apart from its com- patibility with almost all the heavy metal ions, its macroscopic appearance, rigidity and easy availability are important factors, which make seaweed an ideal candidates for heavy metal re- moval from wastewaters (Davis et al., 2003; Aravindhan et al., 2004a,b). Hypnea valentiae is a red macro alga found abundantly in coast- al regions of Southern India. Red macro algae in general find use in food industry as a source of agar and carrageenan. However, the usage of H. valentiae is limited in food industry owing to the pres- ence of lower quantities of these polysaccharides when compared to other red macro algae. Hence, this abundantly available red macro algae H. valentiae has been employed as a biosorbent for cadmium removal. Kinetics of biosorption process and the role of various parameters like pH, temperature initial concentration and adsorbent dosage on the biosorption process have been addressed. 0960-8524/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2009.08.008 * Corresponding author. Tel.: +91 44 24411630; fax: +91 44 24911589. E-mail addresses: aravindhanr78@gmail.com (A. Rathinam), rao_clri@yahoo.com (R.R. Jonnalagadda). Bioresource Technology 101 (2010) 1466–1470 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech