Characteristics of thermodynamic, isotherm, kinetic, mechanism and design equations for the analysis of adsorption in Cd(II) ions-surface modified Eucalyptus seeds system U. Pearlin Kiruba a , P. Senthil Kumar b, *, C. Prabhakaran b , V. Aditya b a EDRC—Civil, Larsen & Toubro Limited, Chennai 600 089, India b Department of Chemical Engineering, SSN College of Engineering, Chennai 603 110, India 1. Introduction Water is the basic needs for all living organisms. The availability of the fresh water in the world is affected/polluted by the over population, unplanned urbanization and industrial activities. This may be due to the discharge of untreated sanitary waste, toxic industrial wastes, dumping of industrial effluents and the runoff from the agricultural fields. In particular, the wastewater from the textile, leather, tannery, electroplating, galvanizing, dyes and pigments, metallurgical, paint and other metal processing and refining industries contains the considerable amount of toxic heavy metal ions. The presence of the heavy metals in the wastewater discharged into the water bodies from these industries always pose a serious threat to the humans and also other living environment, even at very low concentrations. Cadmium is one of the toxic metals used in different industries such as metal plating, battery, metallurgical alloying, mining, ceramics, paints and pigment, chemical and petrochemical industries [1–3]. Cadmium ions are released from these industries with various concentra- tions into the environment. These metal ions are not biodegradable and it can be readily absorbed into the human body through food chain. Cadmium toxicity produces adverse health effects such as bone lesions, cancer, lung insufficiency and hypertension. The drinking water guideline value recommended for this element by the BIS is 0.003 mg/L [4]. Hence the removal and recovery of cadmium ions from water and wastewater is highly important to protect the living environment. Many treatment methods such as coagulation, flocculation, precipitation, solvent extraction, ion exchange, adsorption, reverse osmosis, ultrafiltration and electro- dialysis process have been applied for the removal of toxic metal ions [1–3]. In particular, the adsorption process was identified as an effective and economic method for the removal of metal ions from the wastewater [5–7]. Commercial activated carbon is a widely used adsorbent for the removal of pollutants/contaminants from the water and wastewater [8,9]. However, the cost of the activated carbon was found to be relatively high, which has restricted its widespread applications [10]. This problem induced the search of low-cost adsorbents which are alternative to the existing commercial adsorbents and also to remove the heavy metals from the aqueous solution successfully. Some of the alternative adsorbents were available for the removal of cadmium ions reported is as follows: mango peel waste [11], Scolymus hispanicus L. [12], chemically modified orange peel [13], orange waste [14], almond shell [15], hazelnut shell [15], corn cob [16], Journal of the Taiwan Institute of Chemical Engineers 45 (2014) 2957–2968 A R T I C L E I N F O Article history: Received 14 May 2014 Received in revised form 17 July 2014 Accepted 16 August 2014 Available online 6 September 2014 Keywords: Cd(II) ions Isotherms Intraparticle diffusion Kinetics Boyd kinetic model A B S T R A C T The adsorption of Cd(II) ions from synthetic wastewater was performed using two types of newly prepared adsorbent: (i). Surface modified Eucalyptus seeds by sulphuric acid (SMES-S) and (ii). Surface modified Eucalyptus seeds by hydrochloric acid (SMES-H). SMES-S showed better performance for the Cd(II) ions removal than the SMES-H. The thermodynamics of the Cd(II) ions–SMES system was feasible, spontaneous and exothermic in nature. The maximum monolayer adsorption capacities of the adsorbents were found to be 71.15 mg/g (SMES-S) and 64.16 mg/g (SMES-H). The kinetics of the system followed the pseudo-second order kinetic model. The effective diffusivity values were calculated for the SMES-S: 2.0578  10 11 , 2.2641  10 11 , 2.3382  10 11 , 2.5022  10 11 and 2.5445  10 11 m 2 /s for the initial Cd(II) ions concentration from 20 to 100 mg/L, respectively. The SMES-S can be used as an effective adsorbent for the removal of Cd(II) ions. ß 2014 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +91 9884823425. E-mail address: senthilchem8582@gmail.com (P.S. Kumar). Contents lists available at ScienceDirect Journal of the Taiwan Institute of Chemical Engineers jou r nal h o mep age: w ww.els evier .co m/lo c ate/jtic e http://dx.doi.org/10.1016/j.jtice.2014.08.016 1876-1070/ß 2014 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.