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International Journal of Environment Science and Technology, Vol. 6, No. 4, Autumn, 2009, pp. 629-632 Evaluating the effectiveness of a hybrid sorbent resin in removing fluoride from water 1M. Rahmani Boldaji; 2*A. H. Mahvi; 1,3S. Dobaradaran; 1S. S. Hosseini 1School of Public Health, Tehran University of Medical Science, Tehran, Iran *Corresponding Author Email: ahmahvi@yahoo.comTel.: +98912 321 1827; Fax: +9821 8895 0188 Received 25 June 2009; revised 22 July 2009; accepted 15 August 2009 Code Number: st09069 ABSTRACT In some regions of the world, the concentration of fluoride in groundwater is high. To reduce the amount of fluoride to acceptable drinking water standard, it is highly recommended to treat the water. Fluoride adsorption in aqueous solution by a hybrid resin was studied in this research because of its functional groups likeness with goethite. Kinetic data showed that F adsorption was rapid in the beginning and maximum uptake occurred in within 10 min and equilibrium reached within 100 min. The experimental results showed that fluoride adsorption was influenced by pH of solution and optimum operating pH was in the range of 3 to 5.5. Langmuir model was applicable to the present study and F ions were exchanged with hydroxide ions in nano-scaled structure on the surface of sorbent. This adsorbent with 61 % efficiency is suitable for the regions where F concentration is less than 4 mg/L. Keywords: Fluoride removal; Functional groups; Goethite; Hybrid resin; Langmuir model Introduction Fluoride is an essential mineral that in permissible guideline level (WHO, 2006) is beneficial to mankind in dental protection and excessive intake led to various disorders and diseases such as crippling skeletal fluorosis, brittle bones, cancer (lung and bladder), infertility in women, brain and hepatit damage and Alzheimer syndrome (Chinoy, 1991; Shivarajashankara et al., 2001; Guo et al., 2003; Jamode et al., 2004; Mahvi et al., 2006a; Dobaradaran et al., 2008a). Wide varieties of minerals, including fluorspar, rock phosphate, cryolite, apatite, mica and thermal waters especially with high pH have significant level of F. Aluminum smelters that use the F salt cryolite, brick and iron work, coal fired power stations which discharge wastewater with high F concentrations are contributing to entry F to the environment (De la Puente et al., 1997; Abe et al., 2004; Dobaradaran et al., 2009a) .Groundwater as drinking water is usually the main source of F intake (Dobaradaran et al., 2009b), groundwater with high F concentrations occurs in India, Pakistan, West Africa, Thailand, China, Sri Lanka, Southern Africa, Iraq, Iran, Sudan, Ethiopia, Uganda, Kenya and the United Republic of Tanzania (WHO, 2006; Abdel-Ghani et al., 2007; Kumar et al., 2009) and because of daily fluoride intake importance, there are many studies about fluoride contents in water and black tea (Mahvi et al., 2006b; Nouri et al., 2006; Dobaradaran et al., 2008b). Precipitation, ion exchange (Hichour et al., 1999), membrane separation (Ndiaye et al., 2005) and adsorption (Abe et al., 2004) are examples of several technologies that have been developed for F removal. Among various techniques, adsorption is a promising technology, in which F is concentrated onto a small adsorbent mass. Sorption media, including bone charcoal, activated alumina and clay are packed in columns and used for a period of time; this material after saturating are renewed or regenerated. Several researches have been studied and confirmed with a large number of natural materials (Magnesite, natrolite, clinoptilolite, goethite, kaolinite, bentonite, zeolite(s), serpentine, alkaline soil, kaolinitic clay, China clay) for F removal (Bower and Hatcher, 1967; Rao and Viraraghavan, 2002; Fan et al., 2003). Iron and aluminum oxides such as GFH (Kumar et al., 2009), goethite (Jinadasa et al., 1993), activated alumina (Hiemstra and Van Riemsdijk, 1999; Ku and Chiou, 2002) and alumina cement granules (Tang et al. 2009) play an important role in removal of anions from aqueous solutions. In the present study, the adsorption potential of innovative hybrid sorbent (Lewatit FO 36) consisting of a combination of a polymeric anion exchange resin and an iron oxide with a goethite (á-FeOOH) structure has been assessed for F removal from water. This research was performed in Tehran University of medical science from September until December 2008. Materials and Methods Materials Lewatit FO 36 was purchased from the producer (LANXESS Company, Germany). It is a macroporous, monodispersed, polystyrene-based resin which is doped with a nano-scaled film of iron oxide covering the inner surface of the pores of the polymer bead. Appearance of the adsorbent is brown and mean bead size of the material is 0.35 mm. This adsorbent stability is at pH range of 4-14. A stock F solution was prepared by dissolving 221 mg of NaF (Merck) in 1.0 L of distilled water. The pH of distilled water was in the range of 6.8 to 7.3. The batch method by stirring (390 rpm) was used to study the adsorption of F on Lewatit FO 36 and the effects of contact time and pH were investigated. Standard acid and base solutions (0.1N H2SO4 and NaOH solutions) were used for pH adjustment. The pH of solution was measured using pH meter (metrohm E520). Batch experiment with 1000 mL volume were carried out at room temperature (25 ± 2 ºC) by stirring a fixed mass of dry resin and 6 mg/L F solution until equilibrium was reached. After agitation for a specified period of time, solid phase was separated with sedimentation and the concentration of F was determined by UV-vis spectrophotometer (Hatch-Long DR-5000). All experiments were performed in duplicates and the average values were reported. The amount of F adsorbed at time t, qt, was determined from the mass balance equation qt = (C0– Ct ) V / m Results and discussion Effect of pH pH is one of the important factors that influences most of adsorption processes. F adsorption was investigated for 6 mg/L F concentration in the pH range of 3 to 9 as shown in Fig. 2. The highest adsorption of 61 % was observed at pH = 5.5. F adsorption was clearly affected by pH of the solution and decreased with increasing pH (Jinadasa et al., 1993; Ayoob et al., 2008; Kumar et al., 2009) . Surface hydroxyl groups in the structure of functional groups are amphoteric and can act as either an acid or base by adsorbing or desorbing H+. In high pH presence of OH- ions can interference with F adsorption because of the same charge and radius of F and hydroxide ions and the competition for the active site by OH- and electrostatic repulsion of F ions by the negatively charged adsorbent surface at high pH (Ayoob et al., 2008; Kumar et al., 2009). (Any FeOOH dissolution did not appear at pH 3). Effect of contact time F adsorption as a function of contact time was studied for determining the equilibration time. Effect of contact time on amount of F adsorbed with Lewatit FO 36 is shown in Fig. 1. Maximum uptake was obtained within the first 10 min of contact time that increased rapidly and after that rose slowly in the following 100 min. A further increase in contact time had a negligible effect on the adsorption. In some studies a similar trend was also observed during the adsorption of F onto other metal oxy-hydroxide materials (Tang et al., 2009). Equilibrium of adsorption Fruindlich and Langmuir isotherms are useful models for the description of adsorption process by different adsorbents. Equilibrium adsorption of F was conducted at seven different concentrations, ranging from 3 to 6 mg/L at pH = 5.5. The Freundlich model (Freundlich, 1906) refers to surface heterogeneity of the adsorbent: Log (qe) = log K f + 1/n log Ce Where, Kf and 1/n are Freundlich constants, associated with adsorption capacity and adsorption intensity, respectively. The Freundlich plots between log qe and log Ce are shown in Fig 3. Langmuir model assumes uniform energies of adsorption onto the surface and no transmigration of the adsorbate in the plane of the surface. 1/qe=1/qm+1/qmbCe Where, qe is amount adsorbed at equilibrium concentration Ce, qm and b are the Langmuir constants representing adsorption capacity and Langmuir constant energy of adsorption, respectively. The plots of 1/qe as a function of 1/Ce for the adsorption of F are shown in Fig. 3. The monolayer capacity (qm) has been evaluated from intercept of this plots and Langmuir constant (b) has been evaluated from the slope of graph. The plots were found liner with > 0.98 correlation coefficients that showed that Langmuir model was applicable to the present study. This means that the F adsorption is in the form of monolayer coverage on the surface of the adsorbent (Jinadasa et al., 1993). In this study, it has been demonstrated that Lewatit FO 36 can remove fluoride with 61% efficiency where F concentration is less than 4 mg/L. The optimum removal was observed at 3 to 5.5 pH ranges and Langmuir model was applicable for this study. References
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