Journal of Colloid and Interface Science 291 (2005) 588–592 www.elsevier.com/locate/jcis Note Thermodynamic parameters for adsorption equilibrium of heavy metals and dyes from wastewater with low-cost adsorbents A. Ramesh a , D.J. Lee a,∗ , J.W.C. Wong b a Department of Chemical Engineering, National Taiwan University,Taipei 10617, Taiwan b Department of Biology, Hong Kong Baptist University, 224 Waterloo Road, Kowloon Tong, Hong Kong Received 29 January 2005; accepted 26 April 2005 Available online 21 September 2005 Abstract This note revisits the literature evaluating the thermodynamic parameters of adsorption equilibrium uptakes of heavy metals and dyes from water and wastewater streams using low-cost adsorbents derived from agricultural waste, industrial wastes, inorganic particulates, or some natural products. We highlighted the possible flaws in some adsorption studies when their thermodynamic parameters were assessed, since compensation effects during enthalpy and entropy evaluation were possibly overlooked.  2005 Elsevier Inc. All rights reserved. Keywords: Adsorption; Thermodynamics; Heavy metal; Dye; Low-cost adsorbent; Equilibrium 1. Introduction Heavy metals and dyes are found in the wastewater streams of industrial processes, including textiles, paper, paint manufacture, leather tanning, battery manufacture, dyeing, and others; their removal has attracted much practi- cal and academic interest owing to increased concern with their environmental impact. Methods for removing metals or dyes from a water stream include adsorption, which is a highly effective and economical process provided the cor- rect adsorbents are applied in an environment that favors adsorption. Activated carbon is the conventionally adopted adsorbent for removing metals and dyes from water. How- ever, the high cost of activated carbon limits its use as an adsorbent in developing countries. The search for low-cost adsorbents, preferably derived from locally available waste materials, thus has become a main research focus [1,2]. To date, hundreds of studies on the use of low-cost adsorbents have been published. Brown et al. [3] reviewed the pretreat- ment methods used for modifying peat. Shukla et al. [4] * Corresponding author. Fax: +886 2 2362 3040. E-mail address: djlee@ntu.edu.tw (D.J. Lee). reviewed the use of sawdust for removing unwanted mate- rials from water. Babel and Kurniawan [5] reviewed the use of low-cost adsorbents for heavy metals uptake from conta- minated water. Aksu [6] reviewed the use of bioadsorbents to remove organic matter from water. Among the process parameters frequently investigated in the literature, temperature is shown to affect adsorption capacity [7–20]. When adsorption capacity increased with temperature, the process was claimed to be endothermic, and vice versa. The thermodynamic parameters present the es- sential parameters for subsequent engineering evaluation on the ultimate uptake of the adsorbents, and, hopefully, also provide insights to the adsorption mechanisms thus applied for further use in process modification and optimization. 2. Adsorption isotherm model Most adsorption works adopt either the Langmuir or Freundlich isotherm (or both) for adsorption data correla- tion. The Langmuir isotherm is valid for dynamic equilib- rium adsorption–desorption processes on completely homo- geneous surfaces with negligible interaction between ad- 0021-9797/$ – see front matter  2005 Elsevier Inc. All rights reserved. doi:10.1016/j.jcis.2005.04.084