Fluoride removal efficiency from aqueous solution by synthetic iron(III)–aluminum(III)–chromium(III) ternary mixed oxide

Desalination 255 (2010) 44–51

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Desalination j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / d e s a l

Fluoride removal efficiency from aqueous solution by synthetic iron(III)–aluminum (III)–chromium(III) ternary mixed oxide Krishna Biswas, Kaushik Gupta, Arijit Goswami, Uday Chand Ghosh ⁎ Department of Chemistry, Presidency College, 86/1 College Street, Kolkata-700073, India

a r t i c l e

i n f o

Article history: Received 27 July 2009 Received in revised form 5 January 2010 Accepted 27 January 2010 Available online 18 February 2010 Keywords: Adsorption Fluoride Iron(III)–aluminum(III)–chromium(III) mixed oxide Removal

a b s t r a c t Hydrated iron(III)–aluminum(III)–chromium(III) ternary mixed oxide (HIACMO) was synthesized and characterized. FTIR studies confirmed the presence of M–O–M1 type bond in HIACMO. Use of it for investigating fluoride removal efficiency at varied conditions showed that the reaction was pH sensitive, and optimum pH (initial) was between 4.0 and 7.0. The time required to attain dynamic equilibrium was 1.5 h. The pseudo-second order equation described all kinetic data very well. The rate of reaction was multistage diffusion phenomena. The Langmuir isotherm equation described the equilibrium well. Thermodynamic analyzes of equilibriums indicated that the adsorption reaction of fluoride with HIACMO from water was endothermic and spontaneous in nature. The equilibrium solution pH analyzes suggested ion/ligand exchange mechanism for fluoride adsorption. Regeneration of fluoride adsorbed material could be possible up to 90.0 (± 2.0)% with 0.5 M NaOH. 0.2 g of HIACMO reduced fluoride level well below the maximum permissible value from 50.0 ml of fluoride spiked tap water (10.0 mg F− dm− 3) sample. © 2010 Elsevier B.V. All rights reserved.

1. Introduction Fluoride mineral is essential as well as fatal for the dental and skeletal growth of human. It inhibits dental carries at low doses, and accelerates dental and skeletal fluorosis at high doses [1]. Depending upon the body weight, a minimum quantity of fluoride intake is essential for the formation of caries resisting dental enamel and for the normal process of mineralization in hard tissues. The element is metabolized from both electrovalent and covalent compounds. Low fluoride concentrations stabilize the skeletal system by increasing the size of the apatite crystals and reducing their solubility. About 95% of the fluoride in the body deposited in hard tissues, and it continues to be deposited in calcified structures even after other bone constituents (Ca, P, Mg, CO2− and citrate) have reached a steady state. 3 Drinking of water from the groundwater sources is the main route of fluoride intake in rural areas of underdeveloped countries like India. The World Health Organization set up the limits of maximum allowed concentration (MAC) of fluoride (mg dm− 3) in drinking water is 1.0 for the tropical countries and 1.5 for the cooler climatic countries. Thus, the drinking of groundwater that contains fluoride above the MAC level (N1.5 mg dm− 3) is a serious concern to the public health. In India, it is one of the biggest natural calamities. Depending on the geological formation, fluorite (CaF2) and fluoroapatite [3Ca3(PO4)2·CaF2] minerals are hosted in the vein of all most all

⁎ Corresponding author. Tel./fax: + 91 33 2241 3893. E-mail address: [email protected] (U.C. Ghosh). 0011-9164/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.desal.2010.01.019

rocks in sub-surface soil. Surface water rich with bicarbonate when percolated through mineral beds undergoes water–mineral interaction, and releases fluoride due to some chemical reactions [2] under the appropriate geophysical conditions. The fluoride being released mobilizes to the ground water unless any other natural phenomena play any significant role for arresting fluoride from the water that percolates. Saxena and Ahmed [2] suggested that the chemical reactions (R1) and (R2)) below are responsible for the fluoride release from the said minerals when water enriched with bicarbonate percolates from the top of soil surface.

⇌CaCO + 2 F + 2 OH ⇌CaCO

−

CaF2 + 2 HCO3 CaF2 + H2 CO3

−

3

−

3

ðR1Þ

+ H2 CO3 + 2F

−

+ 2 H2 O

ðR2Þ

The fluoride-rich water when percolates over the calcite (CaCO3) hosted rock or soil stabilizes fluoride as fluorite (CaF2) mineral (R3) under geothermal conditions. CaCO3 + 2 F

−

+ H2 O

⇌ CaF

2

−

−

+ HCO3 + OH

ðR3Þ

This freshly formed fluorite, being sparingly soluble (Ksp–10− 11) mineral, would contribute ∼8.0 mg F−/dm3 of water unless any other natural phenomena play any significant role for lowering the fluoride level from percolated water. The natural phenomenon that might be taking place for arresting fluoride from the percolated water is presumed to be the sorption/precipitation onto the composite oxide

K. Biswas et al. / Desalination 255 (2010) 44–51

materials that present in sub-surface soil bed. Thus, it has been presumed that the multimetal mixed oxide may be a good filtering material for scavenging fluoride from the water that contaminated with high fluoride. Traditional treatment methods such as chemical precipitation, membrane process, electro deposition, surface adsorption and ion exchange were investigated for the removal of fluoride from water. In precipitation method, lime and aluminum salts [3,4] were used to reduce fluoride level from industrial wastewater. Typically, lime reduces the fluoride concentration down to 10–20 mg dm− 3. The calcium ions (Ca2+) being released from the lime combine with fluoride, and CaF2 precipitates. The aluminum ions (Al3+) that release from the aluminum − x)+ salt interact with fluoride in water and form AlF(3 , Al(OH)(3 − y)Fy x etc. This reduces fluoride concentration down to 2.0 mg dm− 3 [5]. This method, however, increases pH and total dissolved solids (TDS) of treated water, resulting in a supplementary difficulty of eliminating excess chemicals [6]. The ion exchange, electrodialysis and reverse osmosis methods [6–8] can reduce the fluoride concentration to a suitable value, but expensive for the third world countries like India. Thus, the surface adsorption has been found to be promising for the third world countries like India for easy operation, affordable cost and water quality. The adsorbent materials that had been reported for fluoride adsorption are limestone reactor [9], activated alumina column [10,11], amorphous alumina supported carbon nanotube [12], activated carbon [13], calcite [14], fly ash [15], lanthanum impregnated silica gel [16], red mud [17], some low cost adsorbents [18,19], acid treated spent bleaching earth [20], La3+-impregnated cross-linked gelatin [21], zirconium(IV)-impregnated collagen fibre [22], activated titanium rich bauxite [23], laterite [24,25], quick lime [26], magnetic-chitosan particle [27], montmorillonite [28], light weight concrete materials [29], plaster of Paris [30], KMnO4-modified activated carbon [31], chitin, chitosan and lanthanum-modified chitosan [32], manganese-oxide-coated alumina [33], algal biosorbent Spirogyra sp.-102 [34], calcined Zn/Al hydrotalcite-like compound (HTlc) [35], Fe–Al–Ce trimetal oxide [36], activated alumina [37,38], carbonaceous materials [39], hydrous ferric oxide [40] and hydrated zirconium oxide [41], La(III)-incorporated carboxylated chitosan beads [42], Fe (III)-loaded carboxylated chitosan beads [43] and Fe(III)-loaded ligand exchange cotton cellulose [44]. Some bimetal hydrous oxides such as iron(III)–zirconiun(IV) [45,46], iron (III)–aluminum(III) [47], and iron(III)–tin(IV) [48] were synthesized and used for investigating the fluoride removal efficiency in our laboratory. It had been assumed and specified elsewhere that the multimetal mixed oxides may be the natural key material in scavenging fluoride from the fluoride-rich percolated water. Thus, this manuscript reports the fluoride scavenging efficiency of synthetic hydrated iron(III)– aluminum(III)–chromium(III) trimetal mixed oxide (HIACMO) from the aqueous solution.

2. Materials and methods 2.1. Synthesis of HIACMO To the mixture of MCl3 (where M = Fe, Al and Cr) solution (each 0.1 mol dm− 3 in 0.01 mol dm− 3 of HCl) (v/v = 1:1:1), aqueous ammonia (1:1) was added slowly with mechanical agitation (speed: 1000 rpm) until pH of the solution including gel type precipitate reached to 6.5–7.0. The precipitate was aged with supernatant liquid for 48 h. Decantation off the supernatant liquid; the precipitate was washed thrice with de-ionized water. The filtered precipitate was dried at 60° to 70 °C for 72 h in an air oven. The dried product was grounded to the particles of size 140–290 µm, and heated for 2 h at 120 °C. Finally, the particles were homogenized at pH 5.6 (±0.2) and used for the adsorption experiments.

45

2.2. Reagents A standard stock solution (1000 mg dm− 3) of fluoride was prepared by dissolving sodium fluoride (AR and BDH) in de-ionized water. Sodium 2-(parasulfophenylazo)-1, 8-dihydroxy-3, 6-naphthalene disulfonate (SPADNS) (guaranteed reagent) and zirconium oxychloride (laboratory reagent) used for fluoride estimation were procured from E. Merck (India). All other chemicals used were either analytical or reagent grade. 2.3. Instruments The analytical instruments used for the present work were (1) UV– VIS spectrophotometer (Systronics model 2202) for the colorimetric analysis of fluoride, (2) pH meter (model LI-127, ELICO India) for pH analysis, (3) Jasco 680 plus spectrophotometer for the Föurier transform infrared (FTIR) spectra, and (4) Setaram Analyzer in argon gas atmosphere at a heating rate 20 °C min− 1 over a temperature range up to 900 °C for thermogravimatric (TG) and differential thermal (DT) analyzes. 2.4. Analysis of pHzpc The pH value for the zero point surface charge (pHzpc) of HIACMO was analyzed by pH metric titration method as described by Babic et. al. [49]. 2.5. Experimental methods The influence of initial solution pH (pHi) on the removal of fluoride by HIACMO was conducted using a speed adjustable thermostatic shaker at an agitation speed (ST) = (360 ± 10) rpm and temperature (T) = (30 ± 1) °C. Here, 0.1 g of HIACMO was added with 50.0 mL fluoride solution (initial concentration, C i = 10.0, 25.0 and 50.0 mg dm− 3) at pHi ranged in 3.0–10.0 into a series of polyethylene (PE) bottles (capacity: 250 mL), and agitated for 2.0 h. After filtering the solids from the reaction mixtures, the residual fluoride concentration was analyzed by the SPADNS–zirconyl oxychloride method [50] from the filtrate. For the kinetics of fluoride adsorption, 500 mL fluoride solution (Ci = 10.0 and 50.0 mg dm− 3 and pHi = 5.6 ± 0.2) was put with 1.0 g of HIACMO into a 1.0 L of Borosil glass made beaker. It was placed onto a thermostat to attain at some fixed T (=10°, 30° and 45 °C with a fluctuation of ±1 °C), and agitated with ST = (360 ± 10) rpm. The pH change (if any) with progress of reaction was checked by the online setting of a pH meter electrode, and adjusted by adding either 0.1 M HCl or 0.1 M NaOH. At some pre-fixed time intervals, the samples were withdrawn and filtered immediately. The filtrates were analyzed for the residual fluoride by SPADNS–zirconyl oxychloride method [50] for the calculation of adsorption capacity. For the equilibrium studies, isotherm experiments were conducted by batch procedure described at first paragraph above at pHi = (5. ± 0.2) and at three separate T (= 10°, 30° and 45 °C with a fluctuation of ±1 °C) values taking the Ci of fluoride solution ranged in 10.0 to 80.0 mg dm− 3 and agitation time 1.5 h. The filtered solutions were analyzed for fluoride by the standard method [50], and the adsorption capacity values were calculated. The adsorption amount at any time, t in milligram per unit gram of adsorbent (qt, mg g− 1) was calculated by Eq. (1) as qt

=

½V fCi  Ct g m

ð1Þ

where V is the volume (dm3) of solution, m the weight (g) of HIACMO, and Ci and Ct are the concentration (mg dm− 3) at start (t = 0) and any time t, respectively.

46

K. Biswas et al. / Desalination 255 (2010) 44–51

Similarly, the equilibrium adsorption capacity (qe, mg g− 1) was calculated by Eq. (2) as qe =

½V fCi  Ce g m

ð2Þ

where V, Ci and m have their same significance as above; and Ce is the equilibrium concentration (mg dm− 3) of solute in solution. Regeneration of fluoride adsorbed material was conducted by batch procedure at 30 °C. Here, 0.1 g fluoride adsorbed HIACMO was placed with 50 ml of NaOH solution of varied concentrations (0.1, 0.25, 0.5 and 0.75 M) into separate 250 ml PE bottles and agitated (ST = 360 ± 10 rpm) for 1 h (fixed up from desorption kinetic studies). The filtered solutions were analysed for fluoride concentration, percentage of desorption was calculated.

2.6.1. Kinetic modeling 2.6.1.1. The pseudo-first order model. The Lagergren [51] rate equation is most widely used [23,25,30,31] as a rate equation for assigning the adsorption of an adsorbate from a liquid phase. The pseudo-first order Eq. (3) is represented as: ð3Þ

where qe and qt are the adsorption amount (mg g− 1) at equilibrium and any time, t respectively, k1(min− 1) is the rate constant of pseudofirst order adsorption reaction. The integrated pseudo-first order rate equation at boundary conditions (t = 0 to t = t and qt = 0 to qt = qt) can be written as the following non-linear form (Eq. (4)): qt = qe : ½1− exp ð−k1 :t Þ

ð4Þ

2.6.1.2. The pseudo-second order model. Ho and McKay [52] developed a pseudo-second order kinetic expression for describing the adsorption of some metal ions onto the adsorbent. The form of kinetic rate equation for the pseudo-second order adsorption reaction is expressed as Eq. (5) dqt 2 = k2 ðqe −qt Þ dt

ð7Þ

where kid is the intra-particle (pore) diffusion rate constant (mg g− 1 · time− 0.5). 2.6.2. Isotherm modeling For the modeling of the equilibrium data, the following isotherm equations are used.

qe =

qm bCe 1 + bCe

ð8Þ

where qe and Ce, respectively, are the equilibrium adsorption capacity (mg g− 1) and the equilibrium adsorbate concentration (mg dm− 3). The qm is the monolayer capacity (mg g− 1) and b the equilibrium adsorption constant (dm3 mg− 1). 2.6.2.2. The Freundlich isotherm. H. M. F. Freundlich [56] developed an isotherm model based on multilayer adsorption of an adsorbate on to the heterogeneous surfaces of an adsorbent, which can be expressed as Eq. (9) below 1 =n

ð9Þ

qe = KF Ce

where qe and Ce have the same meaning as noted above. The KF and n are the empirical constants dependent on several environmental factors. 2.7. Thermodynamic parameters Thermodynamic parameters were evaluated using the following standard Eqs. (10)–(12) available in common literature 0

ΔG = − RT ln b

2

k2 qe t 1 + k2 qe t

0:5

ð5Þ

where qe and qt have the same meaning as mentioned above. The k2 (g mg− 1 min− 1) is the rate constant for the pseudo-second order adsorption reaction. The integrated pseudo-second order rate equation at boundary conditions (t = 0 to t = t and qt = 0 to qt = qt) can be written as following non-linear form (Eq. (6)): qt =

qt = kid t

2.6.2.1. The Langmuir isotherm. I. Langmuir [55] developed an isotherm model based on the monolayer coverage of homogeneous surfaces of an adsorbent, which can be expressed by Eq. (8) below

2.6. Theoretical models used for data analysis

dqt = k1 ðqe −qt Þ dt

which differs in form as functions of the geometry of the adsorbent particle [53,54]. Without mathematical detailing, the functional relationship used by many workers [33,38] to predict the rate controlling step (RCS) of an adsorption reaction can be presented by Eq. (7).

ð6Þ

2.6.1.3. Intra-particle diffusion model. The adsorbate moves from the solution phase to the surface of the adsorbent particles in several steps. The overall adsorption process may be controlled by either one or combination of more than one step, such as film or boundary-layer diffusion, intra-particle diffusion, surface diffusion and adsorption into the pore surface or combinations of more than one step. In a rapidly stirred batch process of adsorption, the diffusive mass transfer can be related by an obvious diffusion coefficient, which will fit experimental adsorption rate data. Normally, a process is diffusion controlled if its rate is dependent upon the rate at which components diffuse towards one another. The theoretical treatments of intraparticle diffusion yield rather complex mathematical relationship,

0

0

ΔG = ΔH –TΔS 0

ln b =

0

ð10Þ ð11Þ

0

ΔS ΔH − R RT

ð12Þ

where b is the Langmuir constant in the unit of dm3 mol− 1 at temperature T (K), R is the ideal gas constant (8.314 J mol− 1 K− 1); ΔG0 and ΔH0 are in J mol−1 and ΔS0 is in J mol− 1 K− 1. Thus, the plot of T− 1 (K− 1) versus lnb should be a straight line in accordance to Eq. (12). The slope and intercept of the plot should yield the value of ΔH0 and ΔS 0, respectively. 3. Results and discussion 3.1. Characterization of HIACMO Fig. 1 demonstrates the FTIR spectra of hydrous aluminum (III) oxide (a), HIACMO (b), hydrous iron(III) oxide (c), and hydrous chromium (III) oxide (d). The absorption bands at wave number (ν) value at ∼ 3500 cm− 1 and ∼ 1620–1655 cm−1 are due to the stretching (symmetrical and asymmetrical) and bending modes of vibration for the

K. Biswas et al. / Desalination 255 (2010) 44–51

47

Fig. 3. The effect of initial pH (pHi) on adsorption of fluoride by HIACMO at (30 ± 1) °C. Fig. 1. The Fourier Transform Infrared (FTIR) spectra of (a) hydrous aluminum(III) oxide, (b) HIACMO, (c) hydrous iron(III) oxide and (d) hydrous chromium(III) oxide. −1

O–H groups, respectively. The absorption band at ν ∼ 2360–2370 cm was common in all the four spectra of synthetic oxides which are presumed to be for the carbonate impurity. The FTIR pattern of HIACMO was found to be somewhat different from the hydrous single metal oxides. The sharp band appeared at ν ∼ 1300 cm− 1 may be assigned to the stretching mode of multi centered M–OH bond. The ν values (cm− 1) for symmetrical stretching modes of M–O bonds for the mixed metal oxide (557) shifts towards the lower sides in comparison to the hydrous aluminum oxide (730.2) (a), hydrous ferric oxide (670.6) (c) and hydrous chromium oxide (668) (d). Thus, HIACMO might consist of M– O–M1 type linkages. Fig. 2 demonstrates the variation of equilibrium pH (pHf) from the initial pH (pHi) during experiments. Horizontal portion of Fig. 2 at pHf ranged in 5.5–5.7 should be the pHzpc of HIACMO. Thus, the surface characteristic of the mixed oxide is (i) neutral at pHf = 5.5– 5.7, (ii) positive at pHf b 5.5 and (iii) negative at pHf N 5.7. The TG analysis of HIACMO showed a total loss of weight ∼25.12% up to the drying temperature of 720 °C. ∼88.5% of that took place at around 90°–110 °C. The DT analysis showed that the synthetic mixed oxide was stable up to 700 ° C. The broad and endothermic DT peak at ∼ 200 °C may be due to the elimination of water from the mixed oxide. The results of thermal analyzes indicated that the mixed oxide was hydrated.

of Ci = 10.0, 25.0 and 50.0 mg dm− 3. The results showed (Fig. 3) that the qe of HIACMO had enhanced with increasing pHi from 3.0 to 4.0, and remained nearly constant up to the pHi 7.0. Thereafter, the qe had declined with increasing pHi. Less fluoride adsorption at pHi 3.0 is presumably due to slight solubility loss of the adsorbent. At pHi b 5.50, the positive HIACMO surface (pHzpc = 5.5–5.7) adsorbed fluoride with electrostatic force of attraction (R4) or by exchange of hydroxyl ion on the solid surface (R5) þ

−

þ

−

MOHðSÞ + H3 O + F → MOH2 −−−FðSÞ + H2 O MOH + F

−

þ

þ

+ H3 O →MðsÞ −−−F

−

+ 2 H2 O

ðR4Þ ðR5Þ

At pHi = 5.6, the fluoride adsorption onto the neutral solid surface can be described by the reaction below (R6). δ–

δ +

MO HðSÞ

−

δ–

+ F → MO H

δ +

−

−−−FðSÞ

ðR6Þ

The mechanisms as suggested (R4–R6) are found to be similar to that had been reported for fluoride adsorption by concrete materials [57], alum sludge [58] and activated cerium(IV) oxide/SiMCM-41 adsorbent [59].

3.2. Effect of pH

3.3. Kinetic analysis

Fig. 3 demonstrates the variation on the fluoride adsorption capacity (qe, mg g− 1) of HIACMO with pHi from the fluoride solution

Fig. 4 demonstrates the variation of qt (mg g− 1) against reaction time (t, min.) for the adsorption of fluoride by HIACMO from Ci = 10.0 mg dm− 3 (Fig. 4a) and Ci = 50.0 mg dm− 3 (Fig. 4b) at pHi = (5.6 ± 0.2) and T = 10°, 30° and 45 ° C. It was found that the equilibrium time (te, min) required in reaching highest capacity, qe (mg g− 1) of the adsorbent was about 90 min. The present kinetic data (Fig. 4) were analyzed by the non-linear statistical fit on Microsoft origin 7.0 soft ware spread sheet using Eqs. (4) and (6). The kinetic parameters estimated are shown in Table 1. It was found that the values (mg g− 1) of qt (at any time, t) and qe (at t = te) described the pseudo-second order equation very well (0.99 b R2 b 1.00), and that was better than the pseudo-first order equation (0.95 b R2 b 0.98). The modeled qe values obtained from the pseudo-second order kinetic equation were found very close to the experimental qe. Thus, it had been concluded that the fluoride adsorption reaction with HIACMO takes place obeying the pseudosecond order kinetics under the conditions of experiment. Table 1 shows that the rate constant (k2) and the modeled qe of pseudosecond order kinetics increased, in general, with increasing T on the reaction. The increase of qe value with increasing T indicated that the fluoride adsorption by HIACMO surfaces was endothermic in nature.

Fig. 2. The variation of final pH (pHf) against initial pH (pHi).

48

K. Biswas et al. / Desalination 255 (2010) 44–51

Fig. 4. a. The plot of qt versus t (min) for kinetics of fluoride (Ci = 10.0 mg dm− 3) adsorption on to HIACMO at pHi = (5.6 ± 0.2). b. The plot of qt versus time (min) for kinetics of fluoride (Ci = 50 mg dm− 3) adsorption on to HIACMO at pHi = (5.6 ± 0.2).

Increase of rate constant with increasing T on the reaction may be due to the increase of the number of striking per second by the adsorbate species on the adsorbent sites. 3.4. Intra-particle diffusion If the RCS of fluoride adsorption reaction with HIACMO is intraparticle diffusion, the plot of qt against t0.5 (Weber–Morris plot) [60] should be a straight line in accordance to Eq (7) with intercept value zero. But for the present adsorption process the plots as shown in Fig. 5 (a,b) are non-linear at investigated T and Ci values, which has indicated that the RCS of adsorption process was not solely dependent on intra-particle diffusion. If the points of the plots in Fig. 5 (a,b) are joined, there will be initial curved portions reflecting boundary-layer Table 1 The kinetic parameters estimated for fluoride adsorption onto HIACMO at three different temperatures at pHi = (5.6 ± 0.2). Kinetic models Kinetic parameters

Pseudo-first order

Pseudo-second order

2

χ R2 k1(min− 1) qe (mg g− 1) χ2 R2 k2(mg g− 1 min−1) qe (mg g−1)

Concentration (mg dm−3) 10.0

50.0

10°C

30°C

45°C

10°C

30°C

45°C

0.036 0.982 3.899 0.185 0.002 0.999 0.068 4.206

0.039 0.980 3.919 0.212 0.004 0.998 0.080 4.199

0.043 1.726 2.381 1.160 0.979 0.969 0.960 0.981 3.969 20.263 21.112 21.756 0.242 0.123 0.169 0.183 0.006 0.177 0.492 0.114 0.997 0.997 0.992 0.998 0.094 0.008 0.011 0.012 4.224 22.437 22.996 23.529

Fig. 5. a. The plot of qt versus t0.5 for the fluoride (Ci = 10.0 mg dm− 3) adsorption by HIACMO at pHi = (5.6± 0.2). b. The plot of qt versus t0.5 for the fluoride (Ci = 50 mg dm− 3) adsorption by HIACMO at pHi = (5.6± 0.2).

(film) diffusion effect; and subsequent linear portions attributed to intra-particle diffusion effect indicating slower macro-pore diffusion and slowest micro-pore diffusion. The slowest of the three steps should be the RCS. However, the linear portions of curves did not pass through the origin (Fig. 5a,b) indicating that the mechanism of fluoride adsorption on HIACMO is complex. Thus, it can be concluded that both the surface adsorption as well as intra-particle diffusion contributed to the RCS of fluoride adsorption reaction with HIACMO. Maliyekkal et al. [33] and Ghorai and Pant [38] drew similar conclusion, respectively, on fluoride adsorption by manganeseoxide-coated alumina and activated alumina. 3.5. Adsorption isotherm analysis Fig. 6 demonstrates the plot of Ce versus qe on the adsorption of fluoride by HIACMO at pHi = (5.6 ± 0.2) and T = 10°, 30° and 45 °C. The equilibrium data of Fig. 6 have been analyzed by non-linear regression method on the origin 7.0 soft ware spread sheet using the isotherm Eqs. (10) and (11). Table 2 presents the estimated model parameters. It was found from the estimated parameters (Table 2) that the data described the Langmuir model (0.94 b R2 b 0.96) well, and the goodness of data fit was better than the Freundlich model (0.88 b R2 b 0.91). The monolayer surface coverage, qm (mg g− 1) increased with increase of T on the reaction. At T = 30 °C, the qm obtained was 31.889 mg g− 1. From the analysis of qm values (Table 2), it could be said that the HIACMO surface has good affinity for the fluoride; and also the adsorption process is endothermic in nature. The comparison of qm with some other materials (Table 3) had also

K. Biswas et al. / Desalination 255 (2010) 44–51

49

Table 3 The comparative assessment of Langmuir monolayer adsorption capacity (θ, mg g− 1) of HIACMO at 30°C with some recently developed defluoridation media.

Fig. 6. The plot of Ce versus qe on adsorption of fluoride by HIACMO at pHi = (5.6 ± 0.2).

suggested that the HIACMO should be one of the good medium for the filtration of high fluoride contaminated water. Examination on the favorability of fluoride adsorption reaction with HIACMO taking the value b (Langmuir equilibrium adsorption constant, dm3 mg− 1) (Table 2) by the equation, RL = (1 + b · Ci)− 1, where RL is a dimensionless Langmuir parameter and Ci (mg dm− 3), the initial concentration suggested that the reaction was favorable (RL ranged between 0 and 1.0) even at the concentration of fluoride (Ci) above 1.5 mg dm− 3. 3.6. Thermodynamic parameters The adsorption of fluoride onto the oxide as a function of temperature was investigated. Fig. 7 demonstrates the plot of T− 1 (K− 1) versus lnb in accordance to Eq. (14). The standard enthalpy (ΔH0) and standard entropy (ΔS0) changes were calculated for the reaction from the intercept and the slope of the plot (Fig. 7). The Gibbs' free energy change (ΔG0) was calculated from Eq. (13). The values obtained are shown in Table 4. The negative ΔG0 values had indicated that the adsorption process was spontaneous under the condition reaction. It is also clear from the Table 4 that the ΔG0 values increased gradually with increasing T on the reaction. This had indicated that the spontaneous nature of the adsorption reaction increased with the rising T value. The enthalpy change (ΔH0) value was positive for the reaction, indicating the endothermic nature of the reaction. Thus, the adsorption is favored more with increasing T on the reaction in accordance to the La Chattelier principle. The positive value for the entropy change (ΔS0) reflected that the reaction took

Adsorbent

θ pH and Ci (mg g− 1) (mg dm− 3)

Reference

Algal biosorbent Spirogyra sp.-IO2 Manganese-oxide-coated alumina Magnetic-chitosan Iron–zirconium hybrid oxide Iron–aluminum mixed oxide Iron–tin mixed oxide Quick lime La(III) incorporated carboxylated chitosan beads Fe(III) loaded carboxylated chitosan beads Fe(III)–LECCA HIACMO

1.27 2.851 22.49 8.21 17.73 10.47 16.67 11.91

7.0; 5.0–25.0 7.0 ± 0.2; 2.5–30.0 7.0; 5.0–40.0 (6.8 ± 0.1); 5.0–50.0 (6.9±0.2); 10.0–50.0 (6.4±0.2); 10.0–50.0 6.61; 10.0–50.0 7.0; 11.0–19.0

34 33 27 44 46 47 26 41

15.39

7.0; 11.0–19.0

42

18.55 31.89

5.6; 10.0–200.0 43 (5.6± 0.2); 10.0–80.0 Present work

place with increasing entropy. This is due to the increase of randomness with increase in number of species at the solid–liquid interface when the aquated fluoride from the hydrous phase distributed on to the solid surface of the adsorbent releasing aqua molecules. The magnitude of ΔH0 value had suggested that the adsorption of fluoride by the HIACMO surface was of the physical adsorption type. This means that the attachment of fluoride with HIACMO takes place via electrostatic attraction forces at working pHi. 3.7. Regeneration To check the reversibility of fluoride adsorption reaction with HIACMO, regeneration of fluoride adsorbed material (30.9 ± 1.1 mg g− 1) when treated with NaOH solutions, it was found that the percentages of fluoride released were 75.0 (± 2.0), 81.0 (± 1.6), 89.0 (± 2.0) and 91.0 (± 1.8) with NaOH solution of concentrations 0.1, 0.25, 0.5 and 0.75 M, respectively. Fluoride release above that was not possible even with stronger NaOH solution presumably the pore adsorbed fluoride had not been replaced by aquatic bulky hydroxyl ion. 3.8. Removal of fluoride from spiked tap water To investigate the fluoride removal efficiency of HIACMO, Presidency College tap water was collected and analyzed. The parameters estimated (mg dm− 3 except pH) were Astotal (b 0.01), hardness (149.48), Ca2+

Table 2 The isotherm parameters estimated for fluoride adsorption onto HIACMO at different temperatures and at pHi = (5.6 ± 0.2). Isotherm models

Isotherm parameters

Temperature (°C) 10

30

45

Langmuir

χ2 R2 b (dm3 mg− 1) qm (mg g− 1) χ2 R2 n KF

3.942 0.947 0.236 29.921 7.370 0.901 2.314 7.558

4.136 0.957 0.411 31.889 11.149 0.886 2.880 11.951

6.077 0.944 0.598 33.127 12.946 0.881 2.647 12.835

Freundlich

Fig. 7. The plot of 1/T (K− 1) versus lnb for the estimation of thermodynamic parameters on the adsorption of fluoride by HIACMO.

50

K. Biswas et al. / Desalination 255 (2010) 44–51

Table 4 Thermodynamic parameters estimated on fluoride adsorption by HIACMO at pHi = (5.6 ± 0.2). Temperature (K)

b (dm3 mg− 1)

ΔH0 (kJ mol− 1)

ΔG0 (kJ mol− 1)

ΔS0 (kJ mol− 1 K− 1)

283 303 318

0.236 0.411 0.598

+ 19.819

− 12.856 − 15.160 − 16.902

+ 0.115

− − (49.80), Mg2+ (4.91), HCO− 3 (224.90), F (0.34), Cl (20) and pH (7.90). The fluoride was spiked to the tap water up to the level 10.0 mg dm− 3. The batch adsorption experiment as described in ‘Materials and methods’ was conducted taking 50.0 mL of this fluoride spiked tap water into 250 mL PE bottles with varying HIACMO dose from 0.1 g to 0.6 g, and agitated (speed: 35± 10 rpm) for 1.5 h at 30 (±1.0)°C. Removing the solid by filtration immediate after agitation, the concentration of fluoride in filtrate was analyzed. It was found that the fluoride level reduced with increasing the dose of ternary mixed oxide, and 0.2 g HIACMO dose could reduce fluoride concentration to 0.43 mg dm− 3 from 50.0 mL of fluoride spiked (10.0 mg dm− 3) water sample, which was well below the MCL of fluoride permissible.

3.9. Cost parameter Taking the market prices of the starting materials for HIACMO synthesis plus other costs (25%), it was found that the manufacturing cost per kilogram of the material was around US $28.0. 4. Conclusion For developing efficient material for the fluoride removal filters, iron (III)–aluminum(III)–chromium(III) trimetal mixed oxide (HIACMO) has been synthesized by a simple chemical precipitation method. The characterization from FTIR analysis suggested that the material is hydrated. Use of this material for fluoride adsorption from aqueous solutions showed that the optimum pHi range is 4.0–7.0. The time required is 1.5 h in reaching equilibrium. The kinetic data obeys the pseudo-second order rate equation, and multistage diffusion phenomena control the rate. The equilibrium data describes the Langmuir isotherm model well from which the monolayer adsorption capacity estimated is 31.889 mg g− 1. The present reaction is endothermic (ΔH0 = + 19.819 kJ mol− 1) and spontaneous (ΔG0 = − 12.856 to − 16.902 kJ mol− 1), which takes place with increasing entropy (ΔS0 = + 0.115 kJ mol− 1 K− 1). Feasibility of the reaction increases with increasing temperature on the reaction. The adsorption of fluoride by HIACMO is columbic type. Regeneration of fluoride adsorbed material about 90.0 (±2.0) % with 0.5 M NaOH solution indicates the reversibility of reaction used for fluoride removal. An amount 0.2 g of HIACMO reduces fluoride level well below the maximum permissible value from 50.0 mL of spiked tap water (10.0 mg F− dm− 3) sample. The synthesis cost of material is around US $28.0/kg. Acknowledgements The authors acknowledge sincerely their gratitude to the Principal, Presidency College and the Head, Department of Chemistry, Presidency College, Kolkata, India for the use of laboratory facilities. References [1] A.K. Susheela, Flurosis management programme in India, Curr. Sci. 77 (1999) 1250–1256. [2] V.K. Saxena, S. Ahmed, Dissolution of fluoride in groundwater, Environ. Geol. 40 (2001) 1084–1087.

[3] S. Saha, Treatment of aqueous effluent for fluoride removal, Water Res. 27 (1993) 1347–1350. [4] M. Hichour, F. Persin., J. Sandeaux., C. Gavach,, Fluoride removal from waters by Donnan dialysis, Separ, Purifi.Technol. 18 (2000) 1–11. [5] C.L. Yang, R. Dluhy, Electrochemical generation of aluminium sorbent for fluoride adsorption, J. Hazardous Mater. 94 (2002) 223–238. [6] C. Castel, M. Schweizer, M.O. Simonnot, M. Sardin, Selective removal of fluoride ions by a two-way ion-exchange cyclic processes, Chem. Eng. Sci. 55 (2000) 3341–3352. [7] M. Hichour, F. Persin, J. Molénat, J. Sandeaux, C. Gavach, Fluoride removal from dilute solutions by Donan dialysis with anion-exchange membranes, Desalination 122 (1999) 53–62. [8] A.G. Pervov, E.V. Dudkin, O.A. Sidorenko, V.V. Antipov, S.A. Khakhnov, R.I. Makarov, RO and NF membrane systems for drinking water production and their maintenance techniques, Desalination 132 (2000) 315–321. [9] E.J. Reardon, Y.A. Wang, Limestone reactor for fluoride removal from waste waters, Environ. Sci. Technol. 34 (2000) 3247–3253. [10] Y.C. Wu, Activated alumina removes fluoride from water, J. Water and Sewage Works 125 (1978) 76–87. [11] P.L. Bishop, G. Sansoucy, Fluoride removal from drinking water by activated alumina, J. Am. Water Works Assoc 71 (1979) 554–561. [12] 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 fluoride from water by amorphous alumina supported on carbon nanotubes, Chem. Phys. Lett. 350 (2001) 412–416. [13] M. Srimurali, A. Pragathi, J.A. Karthikeyan, Study on removal of fluoride from drinking water by adsorption onto low cost materials, Environ. Pollut. 99 (1998) 285–289. [14] M. Yang, T. Hashimoto, N. Hoshi, H. Myoga, Fluoride removal in a fixed bed packed with granular calcite, Water Res. 33 (1999) 3395–3402. [15] R. Piekos, S. Paslawaska, Fluoride uptake characteristic of fly ash, Fluoride 32 (1999) 14–19. [16] A.S. Wasay, Md.J. Haron, S. Tokunaga, Adsorption of fluoride, phosphate and arsenate ions on lanthanum impregnated silica gel, Water Environ. Res. 68 (1996) 295–300. [17] Y. Cengeloglu, E. Kir, M. Ersoz, Removal of fluoride from aqueous solution by using red mud, Sep. Purif. Technol. 28 (2002) 81–86. [18] X. Fan, D.J. Parker, M.D. Smith, Adsorption kinetics of fluoride on low cost materials, Water Res. 37 (2003) 4929–4937. [19] A.V. Jamode, V.S. Sapkal, V.S. Jamode, Defluoridation of water using inexpensive adsorbents, J. Ind. Inst. Sci. 84 (2004) 163–171. [20] M. Maharamanlioglu, I. Kizilcikli, I.O. Bicer, Adsorption of fluoride from aqueous solution by acid treated spent bleaching earth, J. Fluorine Chem. 115 (2002) 41–47. [21] Y. Zhou, C. Yu, Y. Shan, Adsorption of fluoride from aqueous solution on La3+impregnated cross-linked gelatin, Sep. Purif. Technol. 36 (2004) 89–94. [22] X.P. Liao, B. Shi, Adsorption of fluoride on zirconium (IV)-impregnated collagen fiber, Environ. Sci. Technol. 39 (2005) 4628–4632. [23] N. Das, P. Pattanaik, R. Das, Defluoridation of drinking water using activated titanium rich bauxite, J. Colloid. Interf. Sci. 292 (2005) 1–10. [24] M. Sarkar, A. Banerjee, P.P. Pramanik, A.R. Sarkar, Use of laterite for the removal of fluoride from contaminated drinking water, J. Colloid. Interf. Sci. 302 (2006) 432–444. [25] M. Sarkar, A. Banerjee, P.P. Pramanik, Kinetics and mechanism of fluoride removal using laterite, Ind. Eng. Chem. Res. 45 (2006) 5920–5927. [26] M. Islam, R.K. Patel, Evaluation of removal efficiency of fluoride from aqueous solution using quick-lime, J. Hazard. Mate. 143 (2007) 303–310. [27] W. Ma, F.Q. Ya, M. Han, R. Wang, Characteristic of equilibrium kinetics studies for the adsorption of fluoride on magnetic-chitosan particle, J. Hazard. Mate. 143 (2007) 296–302. [28] A. Tor, Removal of fluoride from aqueous solution by using montmorillonite, Desalination 201 (2006) 267–276. [29] E. Oguz, Equilibrium isotherms and kinetics studies for the sorption of fluoride on light weight concrete materials, Colloid and surfaces A: Physicochem. Eng. Aspects 295 (2007) 258–263. [30] V. Gopal, K.P. Elango, Equilibrium kinetics and thermodynamics studies of adsorption of fluoride onto plaster of paris, J. Hazard. Mater. 141 (2007) 98–105. [31] A.A.M. Daifullah, S.M. Yakout, S.A. Elreefy, Adsorption of fluoride in aqueous solutions using KMnO4-modified activated carbon derived from stem pyrolysis of rich straw, J. Hazard. Mate. 147 (2007) 633–643. [32] S.P. Kamble, S. Jagtap, M.K. Labhsetwar, D. Thakare, S. Godfrey, S. Tevotta, S.S. Rayalu, Defluoridation of drinking water using chitin, chitosan and lanthanummodified chitosan, Chem. Eng. J. 129 (2007) 173–180. [33] S.M. Maliyekkal, A.K. Sharma, L. Philip, Manganese oxide-coated alumina: a promising sorbent for defluoridation of water, Water Res. 40 (2006) 3497–3506. [34] S.V. Mohan, S.V. Ramanaiah, B. Rajkumar, P.N. Sarma, Removal of fluoride from aqueous phase by biosorption on to algal biosorbent spirogyra sp.-102: sorption mechanism elucidation, J. Hazard. Mater. 141 (2007) 465–474. [35] D.P. Das, J. Das, K. Parida, Physicochemical characterization and adsorption behavior on calcined Zn/Al hydrotalcite-like compound (HTlc) towards removal of fluoride from aqueous solution, J. Colloid Interf. Sci. 261 (2003) 213–220. [36] X. Wu, Y. Zhang, X. Dou, M. Yang, Fluoride removal performance of a novel Fe–Al– Ce trimetal oxide adsorbent, Chemosphere 69 (2007) 1758–1764. [37] S. Ghorai, K.K. Pant, Investigation on the column performance of fluoride adsorption by activated alumina in a fixed bed, Chem. Eng. J. 98 (2004) 165–173. [38] S. Ghorai, K.K. Pant, Equilibrium, kinetics and breakthrough studies for adsorption of fluoride on activated alumina, Sep. Purif. Technol. 42 (2005) 265–271. [39] I. Abe, S. Iwasaki, T. Tokimoto, N. Kawasaki, T. Nakamura, S. Tanada, Adsorption of fluoride ions onto carbonaceous materials, Colloid Interf. Sci. 275 (2004) 35–39. [40] S. Dey, S. Goswami, U.C. Ghosh, Hydrous ferric oxide — a scavenger of fluoride from contaminated water, Water Air Soil Pollut. 158 (2004) 311–323.

K. Biswas et al. / Desalination 255 (2010) 44–51 [41] S. Goswami, S. Dey, U.C. Ghosh, Studies on removal of fluoride by hydrated zirconium oxide, Chem. Environ. Res. 13 (2004) 117–126. [42] N. Viswanathan, S. Meenakshi, Enhanced, fluoride sorption using La(III) incorporated carboxylated chitosan beads, Colloid Interf. Sci. 322 (2008) 375–383. [43] N. Viswanathan, S. Meenakshi, Selective sorption of fluoride using Fe (III) loaded carboxylated chitosan beads, Journal of Fluorine Chemistry 129 (2008) 503–550. [44] Y. .Zhao,, X. Li, L. Liu, F. Chen, Fluoride removal by Fe(III)-loaded ligand exchange cotton cellulose adsorbent from drinking water, Carbohydrate Polymer 72 (2008) 144–150. [45] K. Biswas, D. Bandhoyapadhyay, U.C. Ghosh, Adsorption kinetics of fluorideon iron (III)–zirconium(IV) hybrid oxide, Adsorption 13 (2007) 83–94. [46] K. Biswas, D. Bandhoyapadhyay, U.C. Ghosh, Adsorption of fluoride on synthetic iron (III), zirconium (IV) and binary iron(III)–zirconium(IV) oxides: comparative assessment on pH effect and isotherm, J Environ. Science & Engg. 50 (2008) 153–162. [47] K. Biswas, S.K. Saha, U.C. Ghosh, Adsorption of fluoride from aqueous solution by a synthetic iron (III)–aluminum(III) mixed oxide, Ind. Eng. Chem. Res. 46 (2007) 5346–5356. [48] K. Biswas, K. Gupta, U.C. Ghosh, Adsorption of fluoride by hydrous iron (III)–iin(IV) bimetal mixed oxide from the aqueous solution, Chem. Eng. J. 149 (2008) 196–206. [49] B.M. Babic, S.K. Milonjic, M.J. Polovina, B.V. Kaludierovic, Point of zero charge and intrinsic equilibrium constants of activated carbon cloth, Carbon 37 (1999) 477–481. [50] APHA, AWWA, WEF, in: L.S. Clesceri, A.E. Greenberg, A.D. Eaton (Eds.), Standard Methods for the Examination of Water and Wastewater. 20th Edn, 1998, pp. 4–82, Washington, DC.

51

[51] S. Largergren, Zur theorie der sogenannten adsorption gelöster stoffe, Kungliga Svenska Vetenskapsakademiens, Handlingar 24 (1898) 1–39. [52] Y.S. Ho, G. McKay, Sorption of dye from aqueous solution by peat, Chem. Eng. J. 70 (1998) 115–124. [53] J. Crank, The Mathematics of Diffusion, Clarendon Press, Oxford, 1979. [54] T.W. Weber, R.K. Chakravorty, Pore and solid diffusion models for fixed bed adsorbents, J. Am. Soc. Civ. Engrs. 20 (1974) 228. [55] I. Langmuir, The constitution and fundamental properties of solids and liquids. Part I. Solids, J. Am. Chem. Soc. 38 (1916) 2221–2295. [56] H.M.F. Freundlich, Over the adsorption in solution, Zeitsschrift fur (J. Phys. Chem.) 57 (1905) 385–470. [57] E. Oguz, Adsorption of fluoride on gas concrete materials, J. Hazard. Mate. B117 (2005) 227–233. [58] M.G. Sujana, R.S. Thakur, S.B. Rao, Removal of fluoride from aqueous solution by using alum sludge, J. Colloid Interf. Sci. 206 (1998) 94–101. [59] Y.-M. Xu, A.-R. Ning, J. Zhao, Preparation and defluoridation performance of activated cerium(IV) oxide/SiMCM-41 adsorbent in water, J. Colloid Interf. Sci. 235 (2001) 66–69. [60] W.J. Weber, J.C. Morris, Kinetics of adsorption on carbon from solution, in Proceeding of American Society of Civil Engineers, J. Sanitary Eng. Div. 89 (SA2) (1963) 31–59.