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Removal of fluoride from drinking water by adsorption onto alum-impregnated activated alumina


Separation and Puri?cation Technology 50 (2006) 310–317

Removal of ?uoride from drinking water by adsorption onto alum-impregnated activated alumina
Sushree Swarupa Tripathy a,? , Jean-Luc Bersillon a,1 , Krishna Gopal b,2
a

Laboratoire Environnment et Mineralurgie, ENSG-INPL, Vandoeuvre Les Nancy Cedex, France b Industrial Toxicology Research Centre, Lucknow 226001, UP, India

Received 22 December 2004; received in revised form 24 November 2005; accepted 28 November 2005

Abstract The ability of the alum-impregnated activated alumina (AIAA) for removal of ?uoride from water through adsorption has been investigated in the present study. All the experiments are carried out by batch mode. The effect of various parameters viz. contact time, pH effect (pH 2–8), adsorbent dose (0.5–16 g/l), initial ?uoride concentration (1–35 mg/l) has been investigated to determine the adsorption capacity of AIAA. The adsorbent dose and isotherm data are correlated to the Bradley equation. The ef?cacy of AIAA to remove ?uoride from water is found to be 99% at pH 6.5, contact time for 3 h, dose of 8 g/l, when 20 mg/l of ?uoride is present in 50 ml of water. Energy-dispersive analysis of X-ray shows that the uptake of ?uoride at the AIAA/water interface is due to only surface precipitation. The desorption study reveals that this adsorbent can be regenerated following a simple base–acid rinsing procedure, however, again impregnation of the regenerated adsorbent (rinsed residue) is needed for further de?uoridation process. ? 2005 Elsevier B.V. All rights reserved.
Keywords: Fluoride; Impregnation; Activated alumina; Adsorption; EDAX; Desorption

1. Introduction Fluoride is a naturally occurring element in minerals, geochemical deposits and natural water systems and enters food chains through either drinking water or eating plants and cereals. Fluorine and its compounds are valuable and extensively used in industry such as fertilisers, production of high purity graphite, semiconductors, electrolysis of alumina, etc. Fluoride is bene?cial in human body for the calci?cation of dental enamel and maintenance of healthy bones when present within the permissible limit. But when ?uoride is present in excess of 1.5 mg/l, it causes molting of teeth and lesion of endocrine glands, thyroid, liver and other organs [1,2]. The most commonly symptoms of chronic ?uoride exposures are skeletal ?uorosis, which can lead to the permanent bone and joint deformations and dental ?uo-

Corresponding author. Tel.: +33 3 83 59 62 66/6 26 21 62 91; fax: +33 3 83 59 62 55. E-mail addresses: sushreeswarupa@yahoo.com (S.S. Tripathy), jean-luc.bersillon@ensg.inpl-nancy.fr (J.-L. Bersillon), kgdubey@hotmail.com (K. Gopal). 1 Tel.: +33 3 83 59 62 66; fax: +33 3 83 59 62 55. 2 Tel.: +91 522 2213786; fax: +91 522 2228227. 1383-5866/$ – see front matter ? 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.seppur.2005.11.036

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rosis. According to WHO, the permissible limits of ?uoride in drinking water is 1 mg/l. Fluoride pollution has been observed not only in various minerals and chemical processes but also in some natural water systems over large areas in Asia, Africa, America, Europe, where the ?uoride concentration can range from 0.01 to 3 mg/l in fresh water and 1–35 mg/l in ground water [3]. Due to high toxicity of ?uoride to mankind, there is an urgent need to treat ?uoride-contaminated drinking water to make it safe for human consumption. The most commonly used methods for the de?uoridation of water are adsorption [4,5], ion exchange [6], precipitation [7], Donnan dialysis [2,8] and electrodialysis [9]. Among these methods, adsorption is the most widely used method for the removal of ?uoride from water. Several techniques have been developed for removal of ?uoride from drinking water by adsorption and precipitation processes. Bulusu et al. (1979) developed a technique in which ?uoride can be removed from drinking water by treatment with alkali, chlorine and aluminium sulphate or aluminium chloride or both [10]. Though this technique has been extensively used in India, but due to its high cost, alkaline pH and large dosage, it was not suitable for ?eld application. Recently, Reardon and Wang have proposed a ?uoride

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precipitation technique by using a limestone reactor [11]. But, it is also not suitable for drinkable purpose as it removes ?uoride only up to 2 mg/l. Therefore, an economically viable and easy method for de?uoridation of drinking water is highly desirable. Different materials, which have been used for de?uoridation such as activated alumina [12], amorphous alumina [13], activated carbon [14], low-cost adsorbents such as calcite, clay charcoal, tree bark, saw dust, rice husk, ground nut husk [4,5,15–17] and rare earth oxides [18]. However, the lowest limit for ?uoride reduction by most of the adsorbents is greater than 2 mg/l, therefore, they are not suitable for the drinking water treatment purpose, especially as some of them can only work at an extreme pH value, such as activated carbon which is only effective for ?uoride removal at pH less than 3.0 [19]. Activated alumina has a great capacity for ?uoride adsorption, which is dependent upon the crystalline form, the activation process and the solution pH and alkalinity [20]. The most important factors in?uencing adsorption are pH of water and the crystalline form of the adsorbent. It has been reported that, in case of activated alumina, the optimum pH for maximum adsorption is between 5 and 7 [21,22]. Although activated alumina is considered to be a good adsorbent for the de?uoridation of water, but it could remove ?uoride from water only up to 70% at pH 7, 4 g/l AA and initial ?uoride concentration 13.2 mg/l [22]. The authors experimentally found that at pH 7.5 and 16 g/l AA, 76% of ?uoride can be removed by activated alumina at 12 mg/l initial concentration of ?uoride in the water. In recent years, a considerable amount of work has been done on developing new adsorbents by impregnation of low-cost porous solids with chemicals for better de?uoridation performance [14,17]. Lanthanum(III) and ytterbium(III) impregnated on alumina have shown very promising results for de?uoridation of water [23]. To enhance the adsorption ef?cacy, the surface of activated alumina was modi?ed by impregnation with alum which has a high ?uoride adsorption capacity and this adsorbent is used in the present study. The main objective of this investigation is to study the removal of ?uoride from drinking water using alumimpregnated activated alumina. The removal tests were carried out by varying contact time, effect of pH, adsorbent dose and initial ?uoride concentration. Desorption study was carried out to regenerate the adsorbent so as to reuse it after impregnation with alum. Energy-dispersive analysis of X-ray study was performed for the ?uoride-adsorbed alum-impregnated activated alumina to understand the sorption phenomena at solid/liquid interface. 2. Experimental 2.1. Fluoride solution All the reagents used were of analytical grade. Doubledistilled water was used in all the experiments. A stock solution of 1000 mg/l ?uoride was prepared by dissolving appropriate amount of sodium ?uoride (Merck, Germany) in double-distilled water and all the solutions for removal experiment and analysis were prepared by appropriate dilution from the freshly prepared stock solution.

2.2. Preparation of alum-impregnated activated alumina The activated alumina was impregnated [24] with alum by adding 200 ml of 5% NaHCO3 and 200 ml of 1 M Al2 (SO4 )3 · 16H2 O solution to 100 gm of activated alumina. pH of the solution was maintained 3.4–3.5 by addition of 0.1N HCl. The alum solution remained in the contact with activated alumina until equilibrium was reached. Preliminary runs showed that 3 h were enough for loading. Then the alum-loaded activated alumina was washed thoroughly with double-distilled water until the runoff was clear and dried for 4–5 days at ambient temperature, stored in a reagent bottle. Activated alumina prepared in this way is referred as alum-impregnated activated alumina (AIAA). 2.3. Characterisation of the alum-impregnated activated alumina The X-ray diffraction patterns of AIAA were recorded by a D8 Bruker X-ray diffractometer (Germany). The XRD data were matched with standard JCPDS data ?les. The BET surface area was determined by the low temperature N2 adsorption method. The particle size distribution of the AIAA was measured by using a Malvern Master Sizer, UK. The spectroscopic studies were performed by using a scanning electron microscopy (SEM, Hitachi S 2500) to detect the impregnation of alum on activated alumina and by energy-dispersive analysis of X-ray (EDAX, Thermo NORAN System VANTAGE) to know the sorption mechanism of ?uoride-adsorbed AIAA. The isoelectric point of AIAA was determined by measurement of zeta potential of the charge particle by a zeta-phoremeter. 2.4. Removal of ?uoride by alum-impregnated activated alumina The removal experiments were carried out by batch method. The natural pH of the distilled water is about 6.5 and all the experiments were carried out in room temperature. A known quantity of AIAA and desired concentration of ?uoride solutions were taken in a 100 ml Te?on-coated bottle. The pH of the solution was adjusted by using dilute HCl or NaOH solution. The ?nal volume was made up to 50 ml with distilled water. All the experiments were carried out in a horizontal shaker (HS 501 digital, IKA Labortechnik) at 50 spm. Preliminary investigation showed that 3 h was necessary to attain equilibration. After equilibration period, the suspension was ?ltered through a Whatman no. 42 ?lter paper. The ?ltrate was then analysed for residual ?uoride. The experimental parameters studied are contact time (0–24 h), pH effect (2–12), isotherm experiments at pH 4, 6.5 and 9 with varying ?uoride concentration (1–35 mg/l), adsorbent dose (0.5–16 g/l). The ?uoride concentration was measured with a speci?c ion electrode (ISE25F) by using total ionic strength adjustment buffer (TISAB) solution (58 g of NaCl, 57 ml of CH3 COOH and approximately 150 ml of 6 M NaOH in a volume of 1000 ml) to maintain pH 5.3 and to eliminate the interference of complexing ions. The ?uoride samples and the standard solutions were diluted to 1:1 with TISAB [25]. Fluoride concentration and

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pH were determined by an ion meter (PHM 250, Ion Analyser, France). The instrument was calibrated each time the analysis was done. The amount of ?uoride removal was calculated by subtracting the ?uoride remaining in the solution from initially taken. In all cases, mass balance was con?rmed. 2.5. Desorption study Desorption studies were carried out by using the ?uorideadsorbed AIAA adsorbent. First the ?uoride-adsorbed AIAA is generated by adsorbing 25 mg/l ?uoride solution on 8 g/l AIAA at pH 6.5. After the equilibration, the residue was ?ltered and the ?ltrate was measured for ?uoride content. Then this ?uoride-adsorbed AIAA were subjected for desorption studies by maintaining the pH values (2–12) by addition of 0.1 M NaOH or 0.1 M HCl solution in each ?ask and the suspensions were conditioning for 30 min at 50 spm. Then the suspensions were ?ltered and the adsorbent is neutralised by acid or alkali. 2.6. Data accuracy Each removal experiment was conducted twice to obtain reproducible results with an error of less than 5%. The original ?uoride solution (control) was used in all the analysis that further reduces considerably the absolute error associated with the ?uoride analyser to <3%. 3. Results and discussion 3.1. Characterisation of alum-impregnated activated alumina The X-ray diffraction pattern shows that the adsorbent is well crystallised form with strong basal plane re?ections at 6.11 and

? 3.15 A due to boehmite (Fig. 1). The other important re?ections ? are observed at 2.34, 1.85 and 1.76 A in the diffraction pattern that may be attributed to amorphous precipitate associated to the alum coating on the surface of activated alumina. Fig. 2a and b shows the scanning electron microscope pictures of unimpregnated and alum-impregnated activated alumina, respectively. Fig. 2b shows small particles of amorphous precipitate adhering on boehmite crystal. It is most probable that these particles are amorphous Al(OH)3 . Such type of precipitate is not seen in the unimpregnated activated alumina (Fig. 2a). The speci?c surface area of unimpregnated activated alumina and AIAA as determined by the low-temperature N2 adsorption method were found to be 113 and 176 m2 /g, respectively. On impregnation surface area of impregnated adsorbent should decreases due to the diffusion of impregnating particles into the pores of the adsorbent [26]. But experimentally it is found that the surface area of AIAA increases after impregnation of alum on activated alumina. This increase of surface area might be due to the uniform coating (as amorphous precipitate of Al(OH)3 ) of alum on the surface of the activated alumina hence increases the pore volume. It is believed that the af?nity of the amorphous precipitate of Al(OH)3 on activated alumina in AIAA favours greatly for adsorption of ?uoride. However, the surface area value found for the activated alumina is much smaller than what is usually reported in literature (i.e. 250 m2 /g) [12]. This is attributed to possible variation in the activation technique applied to the alumina. The mean particle size (d50 ) of AIAA is found to be 96 m. 3.1.1. Electrophoretic studies The isoelectric point (iep) of both activated alumina and AIAA were determined by electrophoretic mobility in two different concentrations of NaCl solutions. Fig. 3a and b shows the pH versus zeta potential (mV) curves for activated alumina

Fig. 1. XRD pattern of alum-impregnated activated alumina.

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Fig. 3. Zeta potential of activated alumina and alum-impregnated activated alumina at an ionic strength of (a) 0.001 M NaCl and (b) 0.01 M NaCl.

and neutralised some of the positive charge of the surface, thus causing a decrease in the IEP [14]. As the background electrolyte has considerable effect on the surface of the adsorbents, it is not possible to draw any de?nite conclusion about the exact point of zero charge (pHpzc ) of the adsorbent. However, the potentiometric titration is required to determine the exact pHpzc of the adsorbent. 3.2. Effect of contact time The removal of ?uoride from water with time is shown in Fig. 4. It can be seen from the ?gure that the removal of ?uoride
Fig. 2. SEM micrographs of (a) activated alumina and (b) alum-impregnated activated alumina.

and AIAA at ionic strength of 0.001 and 0.01 M NaCl solution, respectively. The point at which the zeta potential is zero, is called the isoelectric point [27]. The results of the electrophoretic studies show that the IEP values for activated alumina were 8.6 and 7.2 and for AIAA were 9.8 and 8.5 at 0.001 and 0.01 M NaCl solution, respectively. The IEP values for activated alumina and AIAA are not equal in both the electrolyte medium, which implies that the surface of the activated alumina has been modi?ed due to impregnation with alum. The IEP of both activated alumina and AIAA were reduced with increasing ionic strength from 0.001 to 0.01 M NaCl solution. The IEP shift was probably due to the adsorption of background electrolyte (NaCl) used in the electrophoresis measurements. The anions of the electrolyte adsorbed on the surface

Fig. 4. Plot of percent removal of ?uoride as a function of equilibrium time (h) at adsorbent dose 8 g/l, ?uoride concentration 25 mg/l and pH 6.5.

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Fig. 5. Plot of percent removal of ?uoride as a function of pH at adsorbent dose 8 g/l, ?uoride concentration 25 mg/l and equilibrium time 3 h.

increases with increase in time and after 10 min the rate of removal is very fast, i.e. within 10–60 min, most of the ?uoride is removed and reaches a maximum at 3 h and thereafter remains constant. The optimum time to attain the equilibrium is 3 h. The percent of ?uoride removed in 3 h at a constant adsorbate 25 mg/l and adsorbent dose 8 g/l is found to be 92.48%. The sudden rise in removal of ?uoride indicates that the adsorption of ?uoride probably takes place due to the diffusion taking place into the pores on the surface of the adsorbent. 3.3. Effect of pH The most important single factor that controls the adsorption of ions on the oxide surface is the pH of the aqueous solution. Since anion adsorption is coupled with a release of OH? ion, so the adsorption of the ?uoride on the AIAA surface is probably favoured in low pH [28]. The speci?c adsorption of ?uoride on metal oxide is modelled as a two-step ligand-exchange reaction: SOH + H+ SOH2 + + F? SOH2 + SF + H2 O (1) (2)

Fig. 6. Plot of (a) percent removal of ?uoride as a function of adsorbent dose (g/l) at ?uoride concentration 25 mg/l, pH 6.5 and equilibrium time 3 h and (b) log KD value as a function of adsorbent dose (g/l).

3.4. Effect of adsorbent dose and initial ?uoride concentration The effect of adsorbent dosage on the removal of ?uoride from drinking water was studied at pH 6.5 and ?uoride concentration of 25 mg/l for 3 h. The removal of ?uoride increases with an increase in adsorbent dose and attained to maximum of 92% at 8 g/l of AIAA then there is no further removal of ?uoride by increasing the adsorbent dose (Fig. 6a). Therefore, 8 g/l AIAA is used in all the tests. A distribution coef?cient, KD, re?ects the binding ability of the surface for an element and is dependent on pH of the solution and type of surface of the adsorbent. The distribution coef?cient values for ?uoride-adsorbed on AIAA at pH 6.5 was calculated [29] using the following equation: KD = Cs 3 (m /kg) Cw (4)

which combined gives SOH + H+ + F? SF + H2 O (3)

where S represents metal ion. The adsorption of ?uoride on AIAA was studied at different pH values ranging from 2 to 12. The adsorption of ?uoride increases with increased pH, reaches a maximum of 92.6% at pH 6.5, and then decreases with further increase in pH (Fig. 5). The amount of ?uoride removed is slightly decreased in the acidic pH range, may be due to the formation of weak hydro?uoric acid or combined effect of both chemical and electrostatic interaction between the oxide surface and ?uoride ion. At pH above 6.5, ?uoride removal decreases sharply because of stronger competition with hydroxide ions on adsorbent surface even though the oxide surface is positively charge.

where Cs is the concentration of ?uoride on the solid particles (mg/kg) and Cw is the equilibrium concentration in solution (mg/m3 ). Fig. 6b shows that the KD value increases with an increase in adsorbent dose at constant pH that implies the heterogeneous surface of the AIAA. If the surface is homogeneous, the KD values at a given pH should not change with adsorbent dose.

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Fig. 7. Adsorption isotherm of ?uoride onto AIAA at adsorbent dose 8 g/l, equilibrium time 3 h.

The isotherm experiments were carried out at three pH values viz. 4, 6.5 and 9; by varying ?uoride concentration ranging from 1 to 35 mg/l, adsorbent dose 8 g/l and contact time 3 h. Fig. 7 shows that adsorption of ?uoride is high at pH 6.5 as compared to pH 4 and 9. For pH 4 and 6.5, adsorption continues to increase with increased equilibrium concentration, whereas at pH 9 adsorption increases up to 0.1 mmol/l, there after saturation plateau appears that spreads over a very wide concentration range. An attempt has been made to correlate the ?uoride adsorption data to the Bradley equation [30] as follows: (kCeq )n Q = Qmax (1 + kCeq )n (5)

Fig. 8. Equilibrium concentration (mg/l) vs. ?uoride-adsorbed per unit mass of adsorbent (mg/g).

capacity decreases as the pH increases and the af?nity is high at pH 6.5. The values obtained for pH 6.5 is quite similar to the value obtained from Fig. 8. 3.5. EDAX analysis of ?uoride-adsorbed AIAA Energy-dispersive analysis of X-rays was used to analyse the elemental constituents of ?uoride-adsorbed AIAA (obtained from adsorption isotherm studies), shown in Fig. 9. It shows that the presence of ?uoride in small content appears in the spectrum other than the principal elements Al, O, C, and minor elements Na and S. The signal found for Na and S are due to the alum impregnation on activated alumina. EDAX analysis provides direct evidence that ?uoride is super?cially adsorbed on AIAA, thus the reaction may not be due to adsorption but simply surface precipitation. 3.6. Desorption and readsorption capacity To make a cost effective and user-friendly process, the adsorbent should regenerate, so as to reuse for further ?uoride adsorption. The desorption studies were carried out by using 2 g/l ?uoride-adsorbed AIAA (which contains ?uoride concentration 23.15 mg/l) with varying pH by adding 0.1 M HCl or 0.1 M NaOH. Fig. 10 shows that up to pH 8, there is no ?uoride leached. But desorption of ?uoride takes place as the pH increases from 8 to 12 and reaches maximum of 98% at pH 12. The adsorption capacity of regenerated AIAA reduces from 92 to 84% in ?rst time. It shows that the adsorption ef?ciency of the regenerated adsorbent decreases greatly. This might be due to the impregnation of alum is removed from activated alumina at alkaline pH during the desorption process. Therefore, it is necessary to again impregnate the desorbed adsorbent with alum for further use. However, a detail study is needed to determine the reusability of AIAA.

where Q is the amount adsorbed at equilibrium (mg/g); Qmax the maximum adsorption capacity (mg/g); Ceq the equilibrium concentration (mg/l); n a ?tting exponent; k is a constant that is related to a Langmuir isotherm-af?nity (l/mg); such an isotherm equation is indispensable in the design of an adsorber as it allows to calculate the adsorbent dose as a function of initial and target adsorbate concentration. Non-linear least-square regression method was used to parameterise the above equation. Fig. 8 shows the plot of equilibrium concentration versus ?uoride-adsorbed per unit mass of adsorbent. The values obtained from the equation were found to be, Qmax = 40.3 mg/g; k = 2.02 × 10?3 l/mg and n = 0.503. The exponent value n suggests that the adsorption occurs on a highly heterogeneous surface of AIAA, which is already stated above. This is consistence with an adsorption on an amorphous solid like Al(OH)3 . The values obtained from the Bradley equation for the isotherm plot at three pH values are given in Table 1. It shows that the adsorption

Table 1 Parameters derived from the isotherm plots pH 4.0 6.5 9.0 Qmax (mg/gm) 192.65 40.68 19.80 k (l/mg) 3.69 × 10?4 9.04 × 10?3 6.60 × 10?5 n 0.67 0.65 0.50

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Fig. 9. EDAX spectrum of ?uoride-adsorbed AIAA.

Fig. 10. Desorption of ?uoride from the surface of ?uoride-adsorbed AIAA as a function of pH (amount of ?uoride-adsorbed on AIAA 23.15 mg/l, adsorbent dose 2 g/l, equilibrium time 30 min).

capacity decreases as the pH increases and the af?nity is high at pH 6.5 and 8 g/l adsorbent dose is suf?cient for removal of ?uoride from water at the initial ?uoride concentration up to 35 mg/l. (5) EDAX analysis reveals that the ?uoride is present super?cially on alum-impregnated activated alumina. (6) The desorption study shows that the AIAA can be reused for ?uoride removal by rinsing the ?uoride-adsorbed AIAA with 0.1 M NaOH at pH 12 followed by neutralising with 0.1 M HCl. However, the adsorbent can be used for further removal of ?uoride prior to impregnation with alum. (7) Alum-impregnated activated alumina can remove ?uoride effectively (up to 0.2 mg/l) from water containing 20 mg/l ?uoride. Acknowledgments

4. Conclusions From the present investigation, it can be seen that the alumimpregnated activated alumina has better ef?ciency towards removal of ?uoride from drinking water. The following conclusions may be drawn: (1) X-ray diffraction pattern, SEM, electrophoretic studies reveal that impregnation with alum on activated alumina is quite well and uniform. (2) Kinetic study shows that removal of ?uoride was found to be very rapid during the initial period, i.e. most of the ?uoride was removed during 10–60 min and reaches to maximum of 92% at 3 h. (3) The removal of ?uoride increases with increase in pH up to 6.5 then decreases with the increasing pH. The optimum pH was found to be 6.5, which is suitable for the drinkable purpose. (4) The isotherm and variation of adsorbent dose data are correlate to the Bradley equation, which shows that the adsorption This research was done under IFCPAR-CEFIPRA contract no. 2500 W1. Authors are thankful to Prof. Jacques Yvon, Director, LEM, Vandoeuvre for providing necessary research facilities. References
[1] H. Lounici, L. Addour, D. Belhocine, H. Grib, S. Nicolas, B. Bariou, Study of a new technique for ?uoride removal from water, Desalination 114 (1997) 241–251. [2] M. Hichour, F. Persin, J. Sandeaux, C. Gavach, Fluoride removal from water by Donnan analysis, Sep. Purif. Technol. 18 (2000) 1–11. [3] Rajiv Gandhi National Drinking Water Mission, Prevention and Control of Fluorosis in India, 1993. [4] M. Srimurali, A. Pragathi, J. Karthikeyan, A study on removal of ?uorides from drinking water by adsorption onto low-cost materials, Environ. Pollut. 99 (1998) 285–289. [5] E.J. Reardon, Y. Wang, Activation and regeneration of a soil sorbent for de?uoridation of drinking water, Appl. Geochem. 16 (2001) 531–539. [6] K. Vaaramaa, J. Lehto, Removal of metals and anions from drinking water by ion exchange, Desalination 155 (2003) 157–170.

S.S. Tripathy et al. / Separation and Puri?cation Technology 50 (2006) 310–317 [7] G. Singh, B. Kumar, P.K. Sen, J. Majumdar, Water Environ. Res. 71 (1999) 36. [8] T. Ruiz, F. Persin, M. Hichour, J. Sandeaux, Modelisation of ?uoride removal in Donnan dialysis, J. Membr. Sci. 212 (2003) 113–121. [9] Z. Amor, B. Bariou, N. Mameri, M. Toky, S. Nicolas, S. Elmidaoui, Fluoride removal from brackish water by electrodialysis, Desalination 133 (2001) 215–223. [10] K.R. Bulusu, B.B. Sundaresan, B.N. Pathak, W.G. Nawlakhe, D.N. Kulkarni, V.P. Thergaonkar, Fluorides in water, de?uoridation methods and their limitations, J. Inst. Eng. (India)-Environ. Eng. Div. 60 (1979) 1–25. [11] E.J. Reardon, Y. Wang, A limestone reactor for ?uoride removal from wastewaters, Environ. Sci. Technol. 24 (2000) 3247–3253. [12] S. Ghorai, K.K. Pant, Investigations on the column performance of ?uoride adsorption by activated alumina in a ?xed-bed, Chem. Eng. J. 98 (2004) 165–173. [13] Y.H. Li, S. Wang, A. Cao, D. Zhao, X. Zhang, C. Xu, Z. Luan, D. Ruan, J. Liang, D. Wu, B. Wei, Adsorption of ?uoride from water by amorphous alumina supported on carbon nanotubes, Chem. Phys. Lett. 350 (2001) 412–416. [14] R.L. Ramos, J.O. Turrubiartes, M.A.S. Castillo, Adsorption of ?uoride from aqueous solution on aluminium-impregnated carbon, Carbon 37 (1999) 609–617. [15] X. Fan, D.J. Parker, M.D. Smith, Adsorption kinetics of ?uoride on low cost materials, Water Res. 37 (2003) 4929–4937. [17] S.S. Tripathy, S.B. Srivastava, J.L. Bersillon, K. Gopal, Removal of ?uoride from drinking water by using low cost adsorbents, in: Proceedings of the 9th FECS Conference and 2nd SFC Meeting on Chemistry and the Environment, Bordeaux, France, 2004, 352.

317

[18] A.M. Raichur, M.J. Basu, Adsorption of ?uoride onto mixed rare earth oxides, Sep. Purif. Technol. 24 (2001) 121–127. [19] R.H. McKee, W.S. Jhonston, Removal of ?uoride from drinking water, Ind. Eng. Chem. 26 (1984) 849–850. [20] R.L. Ramos, J.A. Martinez, G.R.M. Coronado, Avan Ing. Quim. 3 (1992) 288. [21] F. Rubel, R.D. Woosley, J. Am. Water Works Assoc. 71 (1979) 45. [22] S. Ghorai, K.K. Pant, Equilibrium, kinetics and breakthrough studies for adsorption of ?uoride on activated alumina, Sep. Purif. Technol. 42 (2005) 265–271. [23] S.A. Wasay, S. Tokunaga, S.W. Park, Removal of hazardous anions from aqueous solutions by La(III)- and Y(III)-impregnated alumina, Sep. Sci. Technol. 31 (1996) 1501–1514. [24] J. Karthikeyan, Enhancement of mercury(II) removal from water by coal through chemical pre-treatment, M.Tech. Thesis, IIT, Kanpur, 1982. [25] J.H. Kennedy, Analytical Chemistry Principles, 2nd ed., W.B. Saunders Company, New York, 1990. [26] T.S. Singh, Experimental and modelling studies on ?xed bed adsorption of As(III) ions from aqueous solution, Sep. Sci. Technol., in press. [27] R.J. Hunter, Zeta potential in Colloid Science: Principles and Applications, Academic Press, London, 1988. [28] Y. Cengeloglu, E. Kir, M. Ersoz, Removal of ?uoride from aqueous solution using red mud, Sep. Purif. Technol. 115 (2002) 41–47. [29] L. Sigg, Chemical processes at the particle water-interface, in: S. Werner (Ed.), Aquatic Surface Chemistry, John Wiley & Sons, New York, 1987, p. 325. [30] W. Rudzinski, D. Everett, Adsorption of Gases on Heterogeneous Surfaces, Academic Press, New York, 1992.


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(poly aluminum chloride, 简称 PAC)加入量、 搅拌时间、 初 始氟浓度对除氟...Removal of fluoride from drinking water by adsorption onto alumimpregnated ...
...coconut husk carbon for the removal of arsenic from water_....pdf
removal of arsenic from water_能源/化工_工程科技... alum, ferric sulphate produce a wet bulky ...In the present paper copper impregnated coconut ...