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  • IJRRAS 12 (3) September 2012 www.arpapress.com/Volumes/Vol12Issue3/IJRRAS_12_3_26.pdf

    536

    ADSORPTION- DESORPTION FOR SOME HEAVY METALS IN THE PRESENCE OF SURFACTANT ON SIX AGRICULTURAL SOILS

    Rounak M. Shariff 1

    & Lawen S. Esmail 2

    1,2 The University of Salahaddin- Erbil, College of Science, Department of Chemistry, Kurdistan Region, Iraq

    ABSTRACT

    The present work investigate the effects of surfactant on the sorption of some heavy metals as Zinc, Nicle and

    Copper at different initial concentrations on six selected soil samples through batch equilibrium experiments. The

    pH-adjusted for each metal has been varied from 3 to7. Linear, Freundlich and Langmuir models were used to

    describe the sorption processes. The sorption data fitted very well with both Freundlich and Langmuir isotherm

    model which gave high correlation coefficients. Freundlich coefficient KF values for adsorption process varied

    between 1.582 - 2.121 mlg-1

    , 1.781- 2.054 mlg-1

    and 1.291- 1.958 mlg-1

    for Zinc, Nicle and Copper respectively.

    Langmuir coefficient KL values for adsorption process varied between 0.012 - 0.029 mlg-1

    , 0.017 - 0.057 mlg-1

    and

    0.008- 0.021 mlg-1

    for Zinc, Nicle and Copper respectively. The pseudo- second order kinetic model was most

    agreeable with the experiments. An inionic surfactants sodium dodecyl sulfate (SDS) at critical micelles

    concentration (cmc ) were tested for their adsorption-desorption potential, was found to be fairly effective to

    removal of more than 61, 64, and 68% of sorbed metals Zinc, Nicle and Copper respectively. The Freundlich

    coefficient for desorption processes KFdes values varied between 1.637 - 1.944 mlg-1

    , 1.652- 2.311 mlg-1

    and 1.546-

    2.304 mlg-1

    for Zinc, Nicle and Copper respectively. Langmuir coefficient KLdes values for desorption process varied

    between 0.025 - 0.080 mlg-1

    , 0.083 - 0.117 mlg-1

    and 0.041- 0.222 mlg-1

    for Zinc, Nicle and Copper respectively.

    Keywords: Adsorption- Desorption Isotherms, Zinc, Nicle, Copper, Surfactant.

    1. INTRODUCTION

    Heavy metals are toxic to our environmental quality, and pose a threat to groundwater through that metal

    contaminants can remain on site for long time until they are been removed. Remediation of heavy metal

    contaminated soils represents a formidable challenge [1]. The Sorption of heavy metals onto soil particles affects the

    movement and fate of heavy metals in soil. Therefore, accurate description of the retention or sorption process of

    heavy metal is important. The sorption desorption of heavy metals from soils can affected by many factors as pH,

    temperature, and residence time. The effective remediation of contaminated soils should be explained through the

    mechanism of heavy metal interaction with soil and factors that affect their retention and /or release from these

    particles [2&3].

    Surfactants have shown some potential for remediation of heavy metal from soil. It is possible that surfactant

    adsorption may displace adsorbed metals, thereby mobilizing them. Factors affecting soil washing/soil flushing

    processes include clay content, humic material, metal concentration, particle size distribution/soil texture, separation

    coefficient, and wash solution [4]. The mechanism of surfactant enhanced heavy metal removal from soil surface is

    ion exchange, precipitation-dissolution, and counterion binding [5&6]. It is necessary to take into account the

    characteristics of the surfactant (e.g., chemical structure, hydrophilic-lipophilic balance [HLB], or its concentration

    in the soil-water system, the solubility and hydrophobicity of the characteristics of soil (e.g., OM, clay content)

    [7&8]. The concentration at which micelles form is known as the critical micelle concentration (cmc), surfactants

    above the cmc level may greatly increase the solubility of less hydrophilic organic pollutants. Surfactants are

    classified according to the nature of the hydrophilic portion of the molecule [9&10]. Zinc is the most common

    elements in the earth's crust it is highly soluble and therefore very mobile in aquatic system [11]. Nickel is a very

    abundant natural element. Pure nickel is a hard, silvery-white metal .Nickel is carcinogenic metal and associated

    with reproductive problems and birth defect [12] . Copper is a reddish-colored metal; it has its characteristic color

    because of its band structure [13].

    2. MATERIALS AND METHODS

    2.1. Soils

    Fresh soil samples were collected from six main agricultural locations in kurdistan region representing a range of

    physico-chemical properties. Subsamples of homogenized soils were analyzed for moisture content, organic matter

    content, particle size distribution, texture, pH, loss on ignition and exchangeable basic cations. The detail was

    characterized in our previous article[8].

  • IJRRAS 12 (3) September 2012 Rounak & Esmail Adsorption- Desorption for Some Heavy Metals

    537

    2.2. Metals

    Analytical grad substituted heavy metals (Zn, Ni, and Cu) were selected for adsorption studies. Zn(NO3)2.6H2O

    (fluka AG, Chemische fabrik, CH-9470 Buchs). NiCl2.6H2O (fluka, Garntie,MG 237.71, Switzend). CuCl2.H2O

    (B.D.H.laboratory chemicals, trade mark product No.10088,England). The anionic sodium dodecyl sulphate (SDS),

    ( B.D.H), formula is C18H29SO4Na, and the molecular weight is 448 g moL-1

    , while the cmc is 2.38 gL-1. All chemicals used were of analytical grade reagents and used without pre-treatments. Standard stock solutions of the

    metals were prepared in deionised water.

    2.3. Adsorption Experiments

    Kinetic studies indicated that metal ion adsorption were characterized by a rapid adsorption processes, for Zn, Ni,

    and Cu were carried out through batch method[14&15]. Duplicate air-dried soil samples were equilibrated with

    different metal initial concentration (50, 100, 150 and 200) gml-1

    , were for each metal alone at the soil solution

    ratios 1:10 gml-1

    , in 18 ml glass tube fitted with Teflon-lined screw caps. The samples plus blanks (no metal) and

    control (no soil). The samples were shaken continuously at temperature controlled (25 0C) water bath shaker (185

    rpm) for different contact time intervals (15, 30, 60, 120, 180, 240, 480 and 600) hours. The tubes were centrifuged

    for 20 min. at 3500 rpm. The clear supernatant was removed and analyzed for the metal ion of Zn, Ni, and Cu

    solution with by atomic absorption spectrophotometer AAS. The initial pH solution values were adjusted at 6.0 for

    Zn, 5.6 for Ni, and 5.9 for Cu using 0.1M NaOH and 0.1M HCl. The total amount of metal adsorbed in the

    adsorption processes was calculated from the difference between the amount added initially and that remaining in

    solution after equilibration. The measured liquid phase concentrations were then used to calculate the adsorption

    capacity. Desorption experiments were done as each test tube was placed in a thermostated shaker at 25C after

    equilibration for 24 h with different metals concentrations (50, 100, 150, and 200) g ml-1

    , the samples were

    centrifuged, 5ml of supernatant was removed from the adsorption equilibrium solution and immediately replaced by

    5ml of SDS and was this repeated for four times. The resuspended samples were shaken for (15, 30, 60, 120, 180,

    240, 480 and 600) min for the kinetic study. Desorption of the metal that remained on soil at each desorption stage

    was calculated as the difference between the initial amount adsorbed (the amount of metal sorbed at equilibrium

    concentration corresponding to the initial concentration) and the amount desorbed (after each removing), all

    determinations were carried out in duplicate.

    Competitive metal ion adsorption-desorption between soil and surfactant in the soil-metal-water-surfactant system,

    in the presence SDS, at concentrations of 0.1cmc, cmc, and 10cmc were conducted adsorption-desorption

    isotherms[12&16]. The same procedure were repeated in the presence of SDS for the three metals alone and for the

    same agitation time, and the desorption done by removing 5ml from the adsorption equilibrium solution and

    immediately replaced by 5ml of water and was this repeated for four times.

    3. DATA ANALYSIS

    3.1. Kinetic Model

    The amount of metals adsorbed (qt) per gram of soil (gg-1

    ) at time t, was calculated as follows[14]:

    (1)

    (2)

    (3)

    Co and Ct are the metal concentration in liquid phase at the initial and time t (in g.ml-1

    ) respectively, M is the

    weight of the soil (g), and V is the volume of the solution (ml). For the desorption intestate of (Co : Ce is used

    which means the equilibrium metal concentration), equation 2 calculate the sorption capacity, and equation 3

    calculate the recovery or percent of metal removal. Fig. 1-a,b, and c plotted the R% vis pH for 100 gml-1

    for a-

    Zinc b-Nicle, and c- Copper.

    3.1. 1. Pseudo-First Order Equation

    The pseudo-first order rate expression known as Lagergren equation which describes the adsorption rate based on

    the adsorption capacity, generally expressed as [17&18]:

    M

    VCCq tot *)(

    1000**)(

    M

    VCeCq oe

    0

    100*)(%

    CCeCR o

  • IJRRAS 1

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