Journal of Hazardous Materials 165 (2009) 271–278 Contents lists available at ScienceDirect Journal of Hazardous Materials journal homepage: www.elsevier.com/locate/jhazmat Azadirachta indica leaf powder as a biosorbent for Ni(II) in aqueous medium Krishna G. Bhattacharyya a,∗ , Jyotirekha Sarma a , Arunima Sarma b a Department of Chemistry, Gauhati University, Guwahati 781014, Assam, India b Department of Chemistry, Morigaon College, Morigaon 782105, Assam, India article info Article history: Received 8 June 2008 Received in revised form 6 September 2008 Accepted 29 September 2008 Available online 7 October 2008 Keywords: Adsorption Biosorption Azadirachta indica leaf powder Intra-particle diffusion Isotherm Thermodynamics abstract Azadirachta indica leaves are converted to a fine powder for use as a biosorbent for the removal of metal ions in aqueous solution. In this work, the adsorptive interactions between Ni(II) and the powder were studied under a variety of conditions involving variations in pH, Ni(II) concentration, biosorbent amount, interaction time and temperature, all in single batch processes. The experimental data have been inter- preted on the basis of existing mathematical models of equilibrium kinetics and thermodynamics. The biosorption of Ni(II) increased in the pH range of 2.0–5.0 with ∼92.6% adsorption at pH 5.0 for the high- est amount of the biosorbent (4 g/L). The biosorption followed second-order kinetics and intra-particle diffusion was likely to have significant influence in controlling the process. The Langmuir monolayer adsorption capacity varied from 2.4 to 9.1 mg/g and the equilibrium coefficient from 1.09 to 2.78 L/g with strong indication that the Ni(II) ions were held on the biosorbent surface by formation of an adsorption complex. The thermodynamic parameters showed the process to be exothermic in nature supported by appropriate ranges of values of enthalpy change, entropy change and Gibbs energy change. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Many toxic heavy metals are regularly discharged into the envi- ronment as constituents of industrial emissions, effluents and solid wastes, causing serious soil and water pollution. Even at relatively low concentrations, some of the metal ions could be highly toxic towards plant and animal life [1] and it is necessary to remove and if possible, recover the metals from the industrial discharges before being allowed to interact with the natural environment. Nickel is moderately abundant and is the twenty-second most abundant ele- ment by weight in the earth’s crust [2]. It is mostly found along with sulphides of iron or copper [3]. Nickel is a common pollutant arising from many electroplating and vegetable fat producing industries, metal mining and process- ing as well as other industrial, urban and agricultural activities. Primary base metal smelters are major sources of Ni. The permissi- ble limit of Ni(II) in drinking water is 0.5 mg/L [4]. Ni(II) can cause dermatitis, dizziness, headache, nausea and carcinogenesis. It is also toxic to the plants. Daily intake of nickel from food is 100–300 g/day in most countries. Critical organs for nickel exposure in humans are the res- piratory system, especially the nasal cavities, sinuses and the skin. Exposure to nickel has been known to cause occupational asthma in metal-plating workers [4,5]. Many other respiratory effects due to ∗ Corresponding author. Tel.: +91 361 2571529; fax: +91 361 2570599. E-mail address: krishna2604@sify.com (K.G. Bhattacharyya). exposure to nickel are reported, like chronic sinusitis and bronchi- tis, nasal septal erosions, decreased pulmonary residual capacity, increased respiratory frequency. Nickel and nickel compounds have a strong sensitizing potential on the skin, which is manifested by irritation, eczema and allergic contact dermatitis. Nickel car- bonyl is the most acutely toxic nickel compound. Poisoning can lead to headache, vertigo, nausea, vomiting and severe pneumonia. Chronic irritative effects observed in nickel refinery and nickel- plating workers include rhinitis, sinusitis, perforations of the nasal septum and bronchial asthma. High risks have been reported in nickel refinery workers and workers involved in processes with exposure to soluble nickel e.g. nickel sulphate [6], often combined with some exposure to nickel oxide. Various physicochemical and biological methods are in use for the removal of toxic metal ions from water and the practical appli- cation of these methods are dependent on their operational costs as well as difficulties associated with disposal of wastes gener- ated [1,2–4]. These methods are required to address the inadequacy of the conventional treatment methods of chemical precipitation, evaporation, etc., for treating effluents at low metal loadings [1,5–7] and must represent a cost effective remediation technology [8–12]. Liquid-phase adsorption is one of the most efficient methods for the removal of colors, odors, organic, and inorganic pollutants from industrial effluents. While granular or powdered activated carbon is very effective for relatively low-molar-mass organic com- pounds, the efficiency is much less for metals unless chemically activated [8]. Biosorption, involving use of dead or living biomass, has emerged as a technique with remarkable promise in treating 0304-3894/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2008.09.109