Adsorption of lindane from water onto GAC: effect of carbon loading on kinetic behavior

https://doi.org/10.1016/S1385-8947(01)00223-6Get rights and content

Abstract

Batch kinetic experiments of adsorption of lindane in dilute aqueous solution onto F-400 granular activated carbon (GAC) with different carbon weight and initial concentration were analyzed. Concentration decay of lindane was measured by means of SPME (solid phase micro extraction). A high level of energetic and structural heterogeneity of the F-400 activated carbon was observed by means of TG analysis. An adsorption model including film-, macropore-, and micropore-diffusion based on the branched pore model was fitted to experimental data. The effect of carbon loading on model parameters can be summarized as follows: (i) the effective macropore diffusivity, including pore and surface diffusivity, and the micropore rate coefficient have little dependence on carbon loading, and (ii) the fraction of adsorptive capacity in macropores depends strongly on carbon loading, which is attributed to the difference in adsorptive affinity in macro- and micropores.

Introduction

Organic pesticides have been present in raw water supplies since about 1940. They are toxic and hazardous to various target organisms, including humans. The chemical and biological stability of many pesticides, together with their hydrophobic behavior, has made adsorption onto activated carbon a feasible and effective treatment for their removal. Lindane (γ-isomer of hexachlorocyclohexane) is one example of these compounds [1]. This pesticide has a broad range of application [2], and it is included in the environmental protection agency’s (EPA) list of organic priority pollutants [3]. This contaminant has been detected in surface water sources at residual levels up to 0.15 μg l−1 [4]. There is some information in the literature concerning the adsorption of lindane on activated carbon [1], [5]. These studies show that activated carbon can be used to reduce the concentration of this pesticide down to the potable level, but no information is given about the parameters needed to describe the dynamics of the system. Kouras et al. [4] studied the aqueous adsorption kinetics of lindane onto powdered activated carbon, using an empirical model to describe the experimental results. Although this kind of models are widely used to design adsorption systems, models with a theoretical basis have some advantages in this respect because a wider range of conditions, as well as a larger number of variables, can be considered.

The design of adsorption systems requires to obtain the solute concentration decay curves for the sorbate/sorbent system as the starting point, as well as the adsorption capacity of the sorbent as a function of sorbate concentration (adsorption isotherm). The description of adsorption kinetics involves the comparison of the experimental concentration decay curves with those predicted with a model, which can have an empirical or theoretical basis, in order to estimate the kinetic parameters. Several models can be proposed depending on the mechanism of transport assumed inside the particle, which can be diffusion in the liquid-filled pores, diffusion in the adsorbed phase (surface diffusion) and both mechanisms in parallel. The literature is rich with research work on the description of adsorption systems with theoretical models. The pore diffusion model was used by Liapis and Rippin [6] to describe literature data of the adsorption of alcohols on activated carbon and by Garcia et al. [7] for the adsorption of phenolic mixtures on a polymeric adsorbent. The model that has probably received more attention is the homogeneous solid diffusion model (HSDM), which is based on the assumption that the concentration in the internal liquid-phase is negligible and surface diffusion dominates. This model has been used by Crittenden and Weber [8], [9], Al-Duri and McKay [10] and McKay [11]. Chatzopoulos et al. [12] used this model taking into account that surface diffusivity depends on concentration. Models considering both mechanisms in parallel have been used by Neretnieks [13], Fritz et al. [14], Costa et al. [15] and Calleja et al. [16]. Advanced models take into account the structural heterogeneity of activated carbon by assuming a bidisperse structure [17].

The aim of this paper is to study the adsorption kinetics of lindane onto granular activated carbon (GAC) in a batch system. A wide concentration interval was considered both in equilibrium and kinetic experiments, reaching the maximum level permitted by European legislation (0.1 μg l−1). A model assuming a bidisperse structure (macro- and micropores), each region having different adsorption isotherm, was used to describe the system, and the effect of carbon loading on kinetic behavior was studied by changing both the initial concentration of sorbate and the sorbent weight.

Section snippets

Materials and methods

Lindane (99%) was supplied by Sigma. Alachor (2-chloro-2′,6′diethyl-N-methoxymethylacetanilide) (99.4%) was supplied by Chem Service. Solutions were prepared with distilled water passed through a Milli-Q water purifier (Millipore Corporation). The sorbent was a commercial GAC, Filtrasorb 400, supplied by Chemviron Carbon. The sieve fraction between 0.84 and 1 mm was selected. The activated carbon was stored at 110 °C, boiled in water during 20 min, and cooled by adding water prior to use. The

Model description

A model based on the biporous structure proposed by Peel et al. [17] was used to describe the kinetic behavior of the system lindane–GAC. In this model, the carbon particle is partitioned into two regions: macropores, in which an initial rapid uptake occurs; and micropores, in which restricted diffusion takes place and the remaining capacity to equilibrium is utilized. As micropores branch off macropores, mass transfer proceeds through three different steps coupled in series: (i) mass transfer

Numerical methods

The best parameter values for all the fitting procedures performed in this work were calculated as those that minimize the root mean square (RMS) of the normalized residuals, defined in Eq. (19)RMS=1Ni=1i=Nyexp,i−ycal,iyexp,i212×100where N is the number of experimental points and y the dependent variable. This objective function was used because the range of yexp (concentration) was of several orders of magnitude, all the values of yexp having the same importance in Eq. (19). A fortran

Adsorption equilibrium

Fig. 1 presents equilibrium data for lindane in aqueous solution onto F-400 activated carbon at 25 °C. The experimental points were fitted to several well-known equations for adsorption isotherms. Results are presented in Table 2. The Langmuir isotherm gave the poorest fit, deviating considerably at high liquid concentrations, which can be attributed to the energetic heterogeneity of the activated carbon surface. The Freundlich isotherm yielded a better fit, but this equation cannot account for

Conclusions

Kinetic and equilibrium data were obtained for the adsorption of aqueous lindane onto GAC for long time periods in a batch system. The best fit to equilibrium data among several well-known two-parameters isotherms was given by the Dubinin–Radushkevich equation. By means of TG analysis, a high level of energetic and structural heterogeneity of the sorbent was observed. These results agree with the energetic heterogeneity inferred from the adsorption equilibrium data.

An adsorption model including

Acknowledgements

We gratefully acknowledge financial support from Comunidad Autónoma de Madrid (Project 07M/0350/1997).

References (35)

  • A. Leitao et al.

    Modelling of solid–liquid adsorption: effects of adsorbent heterogeneity

    Chem. Eng. J.

    (1993)
  • E. Ruckenstein et al.

    Sorption by solids with bidisperse pore structures

    Chem. Eng. Sci.

    (1971)
  • R.A. Hyde, Removal of trace organics from water-1-adsorption of haloforms and chlorinated pesticides by granular...
  • K.A. Hassal, The Biochemistry and Uses of Pesticides, Structure, Metabolism, Mode of Action and Uses in Crop...
  • S.D. Faust, O.M. Aly, Adsorption Processes for Water Treatment, Butterworths, Boston,...
  • N.P. Thacker et al.

    Removal technology for pesticide contaminants in potable water

    J. Environ. Sci. Hlth. B

    (1997)
  • A. Garcia et al.

    Binary adsorption of phenol and m-cresol mixtures onto a polymeric adsorbents

    Adsorption

    (1999)
  • Cited by (39)

    • Novel activated cotton as eco-adsorbent for solvent vapor

      2014, Microporous and Mesoporous Materials
      Citation Excerpt :

      It passed a condenser at room temperature before entering into the TGA. The thermal desorption of vapor-adsorbed samples was evaluated via temperature programmed desorption (TPD) with TGA soon after the Vads measurement [17,18]. About 7 mg vapor-adsorbed sample was loaded into the TGA sample holder rapidly after taking out from the chamber.

    • Removal of lindane from an aqueous solution by using aminopropyl silica gel-immobilized calix[6]arene

      2013, Journal of Hazardous Materials
      Citation Excerpt :

      Adsorption of some OCPs by using clay minerals and activated carbon has been widely studied [5–8] because of its simplicity, low-cost and effectiveness, especially for medium or low pollutant concentrations [9,10]. For example, granular activated carbon [11], Rhizopus oryzae biomass [12], clinoptilolite [13] and organo-zeolites [14] have been used for the sorption of lindane from aqueous solutions. Calixarenes [15,16] are belong to the class of cavitands known in host–guest chemistry.

    • Effect of natural particles on the transport of lindane in saturated porous media: Laboratory experiments and model-based analysis

      2013, Journal of Contaminant Hydrology
      Citation Excerpt :

      Therefore groundwater contamination by this pesticide remains a current issue and needs to be solved. Many studies have concentrated on the adsorption and degradation of lindane (e.g., Buser and Mueller, 1995; Elliott et al., 2009; Kouras et al., 1998; Liu et al., 2003; Sotelo et al., 2002), some on its transport through soil and aquifer systems under specific conditions (e.g., Chen and Zhu, 2005; Ehlers et al., 1969a, 1969b), and some on its leachability in soil (e.g., Ali and Jain, 2000; Caicedo et al., 2011). Many investigations on the transport of lindane through saturated porous media failed to understand its removal from groundwater because the evidence that colloidal particles could very well enhance its transport was not considered.

    • Surface diffusion in porous media: A critical review

      2011, Microporous and Mesoporous Materials
      Citation Excerpt :

      The above theoretical models may be readily modified to take into account the heterogeneity of the surface (by considering an energy or pore-size distribution like in the models, Eqs. (37) and (38)), pellets with other than a slab shape (k other than 0), or the presence of dead-end pores (like by Do and Do [64]). In fact, several modifications to the original branched pore kinetic model, Eq. (47), have appeared and have been successfully applied [88–92]. The DP method [10,93–98] was originally developed to study the transport of gases, and it is thus presented here (its related versions and/or recent applications can be found in [99–102], for example).

    View all citing articles on Scopus
    View full text