Journal of Colloid and Interface Science 297 (2006) 489–504 www.elsevier.com/locate/jcis Single, binary and multi-component adsorption of copper and cadmium from aqueous solutions on Kraft lignin—a biosorbent Dinesh Mohan a,c,∗ , Charles U. Pittman Jr. a , Philip H. Steele b a Department of Chemistry, Mississippi State University, Mississippi State, MS 39762, USA b Forest Products Department, Mississippi State University, Mississippi State, MS 39762, USA c Environmental Chemistry Division, Industrial Toxicology Research Centre, Lucknow 226 001, India Received 20 October 2005; accepted 11 November 2005 Available online 20 December 2005 Abstract A new biosorbent for removing toxic metal ions from water/industrial wastewater has been investigated using by-product lignin from paper production. Lignin was extracted from black liquor waste, characterized and utilized for the removal of copper and cadmium from aqueous solutions in single, binary and multi-component systems. Adsorption studies were conducted at different temperatures, lignin particle sizes, pHs and solid to liquid ratios. All the studies were conducted by a batch method to determine equilibrium and kinetic parameters. The Langmuir and Freundlich isotherm models were applied. The Langmuir model fits best the equilibrium isotherm data. The maximum lignin adsorption capacities at 25 ◦ C were 87.05 mg/g (1.37 mmol/g) and 137.14 mg/g (1.22 mmol/g) for Cu(II) and Cd(II), respectively. Adsorption of Cu 2+ (68.63 mg/g at 10 ◦ C and 94.68 mg/g at 40 ◦ C) and Cd 2+ (59.58 mg/g at 10 ◦ C and 175.36 mg/g at 40 ◦ C) increased with an increase in temperature. Copper and cadmium adsorption followed pseudo-second order rate kinetics. From kinetic studies, various rate and thermodynamic parameters such as effective diffusion coefficients, activation energy, and activation entropy were evaluated. Adsorption occurs through a particle diffusion mechanism at temperatures 10 and 25 ◦ C while at 40 ◦ C it occurs through a film diffusion mechanism. The sorption capacity of black liquor lignin is higher than many other adsorbents/carbons/biosorbents utilized for the removal of Cu(II) and Cd(II) from water/wastewater in single and multi-component systems.  2005 Elsevier Inc. All rights reserved. Keywords: Lignin; Black liquor; Multi-component adsorption; Copper; Cadmium; Metal ions removal 1. Introduction Heavy metals are toxic to aquatic flora and fauna even in relatively low concentrations. Some metals can be assimilated, stored and concentrated by organisms [1]. Industries, including mining and electroplating, discharge aqueous effluents contain- ing high levels of such heavy metals as uranium, cadmium, mercury, and copper. Untreated effluents have an adverse im- pact on the environment [2,3]. Cadmium is very toxic, which can cause serious damage to the kidneys and bones. It is best known for its association with itai-itai disease [4]. Cadmium * Corresponding author. Fax: +1 662 325 7611. E-mail address: dm_1967@hotmail.com (D. Mohan). is classified as a soft acid. Cadmium ions have little tendency to hydrolyze at pH values below 8, but above 11 all cadmium exists as its hydroxo-complex [5]. In fresh water at pH 6–8, Cd(II) predominates. CdOH + , Cd(OH) 2 , Cd(OH) 2 , Cd(OH) − 3 , Cd(OH) 2− 4 also exist depending upon the solution pH. The chloro-complexes CdCl + , CdCl 2 , CdCl − 3 predominate in sea water and Cd(II) is present in very small amounts [5]. Free cadmium ions are highly toxic to plants and animals [6]. Cad- mium accumulates in humans, causing erythrocyte destruction, nausea, salivation, diarrhea and muscular cramps, renal degra- dation, chronic pulmonary problems and skeletal deformity [1]. The drinking water guideline recommended by World Health Organization and American Water Works Association (AWWA) is 0.005 mg Cd/l. In many groundwaters that contain bicar- 0021-9797/$ – see front matter  2005 Elsevier Inc. All rights reserved. doi:10.1016/j.jcis.2005.11.023