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Adsorption of Pb(II) ions from aqueous solution by native and activated bentonite Kinetic, equilibri

Journal of Hazardous Materials 179 (2010) 332–339

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Adsorption of Pb(II) ions from aqueous solution by native and activated bentonite Kinetic, equilibri

Adsorption of Pb(II) ions from aqueous solution by native and activated bentonite Kinetic, equilibri

Journal of Hazardous

Materials

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Adsorption of Pb(II)ions from aqueous solution by native and activated bentonite:Kinetic,equilibrium and thermodynamic study

Ali Rıza Kul a ,Hülya Koyuncu b ,∗

a Yuzuncu Yil University,Faculty of Art and Science,Department of Chemistry,65080Van,Turkey b

Forensic Medicine Foundation,Felek Street No.45,06300Kecioren,Ankara,Turkey

a r t i c l e i n f o Article history:

Received 6November 2009

Received in revised form 27January 2010Accepted 3March 2010

Available online 9 March 2010Keywords:Pb(II)

Adsorption Kinetics Equilibrium

Thermodynamic

a b s t r a c t

In this study,the adsorption kinetics,equilibrium and thermodynamics of Pb(II)ions on native (NB)and acid activated (AAB)bentonites were examined.The specific surface areas,pore size and pore-size distri-butions of the samples were fully characterized.The adsorption efficiency of Pb(II)onto the NB and AAB was increased with increasing temperature.The kinetics of adsorption of Pb(II)ions was discussed using three kinetic models,the pseudo-first-order,the pseudo-second-order and the intra-particle diffusion model.The experimental data fitted very well the pseudo-second-order kinetic model.The initial sorption rate and the activation energy were also calculated.The activation energy of the sorption was calculated as 16.51and 13.66kJ mol −1for NB and AAB,respectively.Experimental results were also analysed by the Langmuir,Freundlich and Dubinin–Redushkevich (D–R)isotherm equations at different temperatures.R L separation factor for Langmuir and the n value for Freundlich isotherm show that Pb(II)ions are favorably adsorbed by NB and AAB.Thermodynamic quantities such as Gibbs free energy ( G ),the enthalpy ( H )and the entropy change of sorption ( S )were determined as about −5.06,10.29and 0.017kJ mol −1K −1,respectively for AAB.It was shown that the sorption processes were an endothermic reactions,controlled by physical mechanisms and spontaneously.

© 2010 Elsevier B.V. All rights reserved.

1.Introduction

Among the different heavy metals,lead is one of the common and toxic pollutants released into the natural waters from various industrial activities such as metal plating,oil refining,paint and pigment producing and battery manufacturing [1].Lead can enter the human body through inhalation,ingestion or skin contact.As a result when the body is exposed to lead,it can act as a cumula-tive poison.Lead accumulates mainly in bones,brain,kidney and muscles and may cause many serious disorders like anemia,kidney diseases,nervous disorder and sickness even death [2–4].Lead can replace calcium,which is an essential mineral for strong bones and teeth,while play important role in sympathetic actions of nerve and blood vessel for normal functioning of nervous system.It also acts as an enzyme inhibitor in body,e.g.,replaces essential element zinc from heme enzymes.The high level of lead damages cognitive development especially in children [5].Due to toxic effects of lead ions,the removal of them from waters and wastewaters is impor-tant in terms of protection of public health and environment [6].

∗Corresponding author at:Forensic Medicine Foundation,Felek street No:45,06300Kecioren,Ankara,Turkey.Tel.:+903123407324;fax:+903123406629.

E-mail address:hkoyuncu@yyu.edu.tr (H.Koyuncu).The conventional methods for heavy metal removal from water and wastewater include oxidation,reduction,precipitation,reverse osmosis,ion exchange,electrolysis and adsorption.Among all the methods adsorption is highly effective and economical [7].How-ever,the main disadvantage of adsorption treatment is the high price of the adsorbents,which increases the price of wastewater treatment.Thus,adsorbents with low cost and high efficiency for Pb(II)adsorption should be developed.Clay minerals have great potential as inexpensive and efficient adsorbents due to their large quantities,chemical and mechanical stability,high specific surface area,and structural properties.Bentonite is mainly composed of montmorillonite,which is a 2:1-type aluminosilicate.The inner layer is composed of an octahedral sheet situated between two SiO 4tetrahedral sheets.Substitutions within the lattice structure of trivalent aluminium for quadrivalent silicon in the tetrahedral sheet and of ions of lower valence,particularly magnesium,for trivalent aluminium in the octahedral sheet result in a net neg-ative charge on the clay surfaces.The charge imbalance is offset by exchangeable cations such as H +,Na +or Ca 2+on the layer surfaces [8–10].In aqueous solutions,water molecules are inter-calated into the interlamellar space of bentonite,leading to an expansion of the minerals [11].The chemical nature and pore structure of bentonites generally determine their adsorption abil-ity [12,13].Treatment of clay minerals with concentrated inorganic acids usually at high temperature is known as acid activation.

0304-3894/$–see front matter © 2010 Elsevier B.V. All rights reserved.doi:10.1016/j.jhazmat.2010.03.009

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