The investigation of kinetic and isotherm of fluoride adsorption onto functionalize pumice stone

https://doi.org/10.1016/j.jhazmat.2012.03.003Get rights and content

Abstract

In this research work, pumice that is functionalized by the cationic surfactant, hexadecyltrimethyl ammonium (HDTMA), is used as an adsorbent for the removal of fluoride from drinking water. This work was carried out in two parts. The effects of HDTMA loading, pH (3–10), reaction time (5–60 min) and the adsorbent dosage (0.15–2.5 g L−1) were investigated on the removal of fluoride as a target contaminate from water through the design of different experimental sets in the first part. The results from this first part revealed that surfactant-modified pumice (SMP) exhibited the best performance at dose 0.5 g L−1, pH 6, and it adsorbs over 96% of fluoride from a solution containing 10 mg L−1 fluoride after 30 min of mixing time. The four linear forms of the Langmuir, Freundlich, Temkin and Dubinin–Radushkevich isotherms model were applied to determine the best fit of equilibrium expressions. Apart from the regression coefficient (R2), four error functions were used to validate the isotherm and kinetics data. The experimental adsorption isotherm complies with Langmuir equation model type 1. The maximum amount of adsorption (Qmax) was 41 mg g−1. The kinetic studies indicated that the adsorption of fluoride best fitted with the pseudo-second-order kinetic type 1. Thermodynamic parameters evaluation of fluoride adsorption on SMP showed that the adsorption process under the selected conditions was spontaneous and endothermic. The suitability of SMP in defluoridation at field condition was investigated with natural groundwater samples collected from a nearby fluoride endemic area in the second part of this study. Based on this study's results, SMP was shown to be an affordable and a promising option for the removal of fluoride in drinking water.

Highlights

► Removal of fluoride from drinking water. ► Pumice as adsorbent functionalized by the cationic surfactant. ► Effects of HDTMA loading. ► Best fit of equilibrium expressions. ► Maximum amount of adsorption.

Introduction

Fluoride is the first element of the halogen family in the periodic table that does not occur in the element state in the environment due to its high reactivity [1]. The presence of fluoride in drinking water in acceptable concentrations is known as an essential constituent for human health, especially in children below 8 years of age [2]. However, when fluoride concentration exceed the acceptable level (1.5 mg L−1), it leads to serious health problems such as skeletal fluorosis, mottling of teeth and lesions of endocrine glands, thyroid, liver and some other organs. Fluoride compounds are used in industry for a wide range of applications, such as: aluminum production, glass fiber [3], phosphate fertilizers, bricks, tiles, ceramics [3], [4], drinking water fluoridation and toothpaste [5]. Weathering of rocks and industrial discharges are the main sources of fluoride in water, air, and soil [1]. In some provinces of Iran, the level of fluoride in drinking water is greater than 1.5 mg L−1, which can lead to endemic fluorosis. This problem is visible in several countries, including China, the United States, Tanzania, Mexico, Kenya, Poland and Pakistan [2]. The levels of human daily exposure/intake of fluoride mainly depend on the geographical conditions and lifestyles [6]. Potable water is the main source of fluoride intake in humans. As previously stated, water in many places of the world contains high concentrations of permissible fluoride ions. Therefore, treatment of fluoride-contaminated water to a level below the permissible value that is recommended by the WHO has become a critical health issue.

Several methods, such as reverse osmosis, ion exchange/adsorption, coagulation, precipitation, and electro coagulation have been used for the removal of excess fluoride from drinking water [7], [8], [9]. Among these methods, adsorption is the most extensively used and is a promising technique for the removal of fluoride. A large number of materials such as activated alumina, red mud, quartz, and fly ash have been suggested for the adsorption of fluoride from water [2], [10], [11], [12]. However, in recent years, studies have been devoted to low-cost materials such as local mineral sorbents for the elimination of pollutants from water. These sorbents can be used in natural or modified forms. One such low-cost material is pumice [13], [14], [15], [16].

Pumice is a light, porous, volcanic stone with a large surface area. It is easily and cheaply found in nature or some kinds of waste. Pumice is composed of highly microvesicular glass pyroclastic with very thin, translucent bubble walls of extrusive igneous rock. Pumice is commonly pale in color, ranging from white, cream, blue, or grey, to green-brown or black. It is formed when volcanic gases exsolving from viscous magma nucleate bubbles, which cannot readily decouple from the viscous magma prior to chilling to glass [16], [17]. It is a common product of explosive eruptions (plinian and ignimbrite-forming) and commonly forms zones in upper parts of silicic lavas. Pumice has an average porosity of 90%, and initially floats on water [18], [19], [20], [21].

Pumice has been widely tested and used in water treatment as an adsorbent, filter bed and support media [17], [18], [20]. Akbal studied the adsorption of phenol and 4-chlorophenol onto surfactant-modified and unmodified pumice from an aqueous solution. Experimental results showed that unmodified pumice cannot adsorb the phenol compound, but modified pumice is an excellent adsorbent of phenol and 4-chlorophenol [22]. Since pumice is a low-cost material with a porous structure and a large surface area widely available and easily processed and modified, thus modified pumice stone would be a suitable candidate as an adsorbent.

Due to the aforementioned advantage of original and modified pumice, to develop its application for removal of pollutant, it is very beneficial to study the performance of surfactant-modified pumice in eliminating other contaminates, such as fluoride. As mentioned above, several methods and many adsorbents in literature have been used to remove fluoride from water; however, to our knowledge from reviewing the literature, pumice and surfactant-modified pumice used for fluoride removal have not yet been reported. Accordingly, in this work, the capabilities of pumice and surfactant-modified pumice were evaluated in the removal of fluoride from water. The main aim of this study is to demonstrate the performance capacity of modified pumice to adsorb fluoride from drinking water. A series of experiments such as surfactant loading, pH, adsorbent dosage, contact time, and environmental water quality was carried out to investigate their effects on the fluoride adsorption capacity of modified pumice. The kinetics and isotherms of fluoride adsorption with modified pumice stone were also studied.

Section snippets

Sorbent

Pumice stone was supplied from Tikmadash mine, located in the south of East Azerbaijan province, in the northwestern area of Iran. It was washed with distilled water several times and dried out at room temperature. The desired particle size (mesh 80–100) of pumice was obtained from sieve pumice, which had been grinded previously. The characteristics of the natural pumice and its modified form were determined by evaluating surface morphology, specific surface area, pore size and volume, and

Pumice characterization

SEM was used to observe the natural and modified pumice morphology, and micrographs are shown in Fig. 1, Fig. 2. The image of the original pumice (Fig. 1) indicated that the pumice surface had a porous surface. The SEM modified pumice (SMP2) is given in Fig. 2. As seen in Fig. 2, the surfaces of original pumice clearly changed after modification, and porous surface could not be seen clearly. The reason is that the external surface of pumice was covered by surfactant (Fig. 2). In other words,

Conclusion

The findings of this study revealed that functionalized original Iranian pumice caused a decrease in its surface area, due to pore blocking. The adsorption process is pH dependent, and the optimum pH was 6. The kinetic studies showed that the adsorption data are fitted well to the pseudo-second order model (type 1). Furthermore, the isotherm equilibrium studies confirmed that the Langmuir-1 form is the best-fitted model for the adsorption process of fluoride by modified pumice. The maximum

Acknowledgements

The authors are grateful to the Hamadan University of Medical Sciences for its technical and financial support of this research.

References (47)

  • A.M. Yusof et al.

    Removal of Cr(VI) and As(V) from aqueous solutions by HDTMA-modified zeolite Y

    J. Hazard. Mater.

    (2009)
  • U. Wingenfelder et al.

    Sorption of antimonate by HDTMA-modified zeolite

    Microporous Mesoporous Mater.

    (2006)
  • Sh. Wang et al.

    Removal of fulvic acids using the surfactant modified zeolite in a fixed-bed reactor

    Sep. Purif. Technol.

    (2006)
  • F. Akbal

    Adsorption of basic dyes from aqueous solution onto pumice powder

    J. Colloid Interface Sci.

    (2005)
  • M. Kitis et al.

    Adsorption of natural organic matter from waters by iron coated pumice

    Chemosphere

    (2007)
  • G. Neri et al.

    Zeolitized-pumice as a new support for hydrogenation catalysts

    Catal. Commun.

    (2008)
  • F. Akbal

    Sorption of phenol and 4-chlorophenol onto pumice treated with cationic surfactant

    J. Environ. Manage.

    (2005)
  • K. Athanasiadis et al.

    Influence of chemical conditioning on the ion exchange capacity and on kinetic of zinc uptake by clinoptilolite

    Water Res.

    (2005)
  • J.J. Orfao et al.

    Adsorption of a reactive dye on chemically modified activated carbons—influence of pH

    J. Colloid Interface Sci.

    (2006)
  • M. Kitis et al.

    Heterogeneous catalytic degradation of cyanide using copper-impregnated pumice and hydrogen peroxide

    Water Res.

    (2005)
  • B. Ersoy et al.

    Characterization of acidic pumice and determination of its electrokinetic properties in water

    Powder Technol.

    (2010)
  • M. Rožic et al.

    Sorption phenomena of modification of clinoptilolite tuffs by surfactant cations

    J. Colloid Interface Sci.

    (2009)
  • A.A.M. Daifullah et al.

    Adsorption of fluoride in aqueous solutions using KMnO4-modified activated carbon derived from steam pyrolysis of rice straw

    J. Hazard. Mater.

    (2007)
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