Sorptive Removal of Phenol by Zeolitic Bagasse Fly Ash: Equilibrium

Article pubs.acs.org/jced

Sorptive Removal of Phenol by Zeolitic Bagasse Fly Ash: Equilibrium, Kinetics, and Column Studies Ritesh Tailor,*,† Bhavna Shah,† and Ajay Shah‡ †

Department of Chemistry, Veer Narmad South Gujarat University, Surat-395007, Gujarat, India Science and Humanities Department, Vidyabharti Polytechnic Trust, Umrakh, Bardoli-394 345, Surat, Gujarat, India

‡

S Supporting Information *

ABSTRACT: The bagasse fly ash (BFA) has been altered to zeolitic materials by hydrothermal (CZBFA) and fusion (FZBFA) methods. The dominant zeolitic phases identified by powder X-ray diffraction (PXRD) are phillipsite and analcime. The X-ray fluorescence (XRF), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) techniques were used for the determination of chemical composition, functional groups, and morphology of synthesized materials. The phenol sorption capacities of prepared zeolitic and virgin material were determined by batch and column modes. The Langmuir, Freundlich, Dubinin− Radushkevich, and Temkin isotherms were estimated for the sorption nature and efficiency of sorbents. The sorption kinetics is better reflected by the pseudosecond-order model, and thermodynamics parameters exhibited the specified endothermic nature of sorption. The overall sorption was approximated well by film diffusion and pore diffusion simultaneously. The regeneration of sorbents was carried out with HCl, NaOH, and sodium dodecyl sulfate (SDS) detergent. The breakthrough curves capacities obtained by column studies exhibited a lower sorption capacity than the batch method. FZBFA showed the highest capacity of phenol sequestration. The improved capacities of modified zeolitic material may provide a cheap alternative for phenol bearing wastewater.

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water are 1.07·10 −2 mmol·kg−1 and 1.07·10 −2 mmol·kg−1, respectively.4,5 It has been a big challenge to minimize or complete deduction of phenol and its derivative from contaminated wastewaters to maintain the quality of fresh water. Conventional processes available for the removal of phenolic compounds include extraction, steam-distillation, and bacterial and different advanced chemical techniques published earlier.4,6−12 Most of them fail to reduce the pollutants in wastewater up to their acceptable limits at reasonable cost. In wastewater treatments, the sorption technique is most often practiced because of its easiness and large options for the sorbents. Among all of the sorbents, the activated carbon, porous silicates, and polymers are most frequently used for the removal of pollutants as they are very efficient and available in variable sizes with different porous forms.13 The use of these sorbents is limited due to their cost and regeneration troubles. For the adaptation of the sorption technique at an affordable cost, it is essential to have economical sorbents for treatment. In search of low cost sorbents, numbers of researchers have utilized coal fly ash for zeolite preparation,14−19 but the conversion of bagasse fly ash (BFA) into zeolites is not reported in literature, except in our earlier studies.20 The synthesis of

INTRODUCTION Environmental pollution and other environmental problems have become important with the increase of world's population and development of industrial applications. From the beginning of the 20th century there has been a huge growth in the manufacturing and use of synthetic chemicals to satisfy the increasing demands of population. These activities have unloaded numbers of poisonous chemicals into natural environmental bodies. Their excessive amount has deleterious effects on all living biota in their respective environment. Among various organic pollutants, phenol and its analogues have been the subject of great concern, as they are toxic in nature and have an adverse effect on receiving bodies. They are recognized as a priority class of pollutants by U.S. Environmental Protection Agency.1 Phenol has wide applications in different chemical industries for specific chemical reactions which load different forms of phenol into the nearest water bodies beyond their permissible limits.2 Some phenolic compounds, even present in very small concentrations (5.33·10−2 μmol·kg−1), can cause disagreeable odor, particularly when water systems containing phenols are chlorinated for disinfection, generating chlorophenols.3 Due to the toxic and nonbiodegradable nature of phenol, it is necessary to set a rigid setup for its acceptable limits. The maximum acceptable concentrations of phenol recommended by the Ministry of Environment and Forest in the industrial wastewater and by World Health Organization (WHO) in potable and drinking © 2012 American Chemical Society

Received: December 4, 2011 Accepted: April 23, 2012 Published: May 2, 2012 1437

dx.doi.org/10.1021/je300399y | J. Chem. Eng. Data 2012, 57, 1437−1448

Journal of Chemical & Engineering Data

Article

by scanning electron microscopy (SEM, Hitachi S-3400N, Germany). The moisture contents of the sorbents were carried out using Karl Fischer (1204R of VMHI, Metrohm Ltd., USA) instrument. The point of zero charge (pHpzc) values of BFA, CZBFA, and FZBFA were ascertained by mass titration.21 Batch Sorption. Sorption technique was executed with 25 mL of 1.07 mmol·kg−1 initial concentration (C0) of phenol (except concentration study) at a 303 K temperature (except temperature study) using a (75 to 90) μm particle size of the sorbents (BFA, CZBFA, and FZBFA). The sorbent loaded solution was stirred in 50 mL airtight stoppered conical flasks at 150 rpm until equilibrium was attained. The effect of different operational variables, namely, agitation time (1 to 24) h, pH (2 to 12), dosage (0.5 to 10) g·L−1, initial phenol concentration (5.3·10−1 to 3.2) mmol·kg−1, and temperature (303 to 333) K were examined for the sorption of phenol on all three sorbents. After fixed time intervals, an aliquot was taken and tested for phenol concentration at λmax = 270 nm using a UV−visible spectrophotometer (UV−visible EV 300, Thermo Nicolet, USA). Simultaneously, to minimize the error, the study of blank experiments was done for each condition without sorbent to check any sorption by experimental vessels and separating paper which displayed no significant change in the residual phenol concentration. Each experiment was repeated thrice, and the average values were reported. The error bars presented in the graphs are obtained using Origin Pro 8.0 software at the value of 5 %. The required pH was obtained with 1 M NaOH or HCl. The amount of phenol removal, qe (mg·g−1), was computed by eq 1.

low-cost zeolitic sorbent from BFA and examination of their ability in the removal of phenol from simulated water at different operational conditions were the aim of this research. The efficiency of sorption by the sorbents has been evaluated by the applicability of Langmuir, Freundlich, Dubinin−Radushkevich (D-R), and Temkin isotherms. The sorption kinetics was examined by pseudofirst- and second-order models. The dynamic studies of phenol sorption were approximated by applying external diffusion, intraparticle diffusion, mass transfer, and rate expression equations. For practical utility of the synthesized zeolites and BFA, column studies were carried out, and its parameters have been evaluated.

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MATERIALS AND EXPERIMENTAL SECTION Materials. Stock solution (10.66 mmol·kg−1) of phenol (Rankem, India, 0.999 mass fraction, analytical reagent grade used as received) was prepared in doubly distilled water, diluted to desired concentration during sorption experiments. The raw material (BFA) was acquired from a local sugar mill, Shree Khedut Sahkari Khand Udhyog Mandali Ltd., Bardoli, Gujarat, India. BFA was washed thoroughly using double-distilled water, then dried in sunlight for 8 h and 4 h in a hot air oven at 353 ± 5 K. The dried BFA, sieved through (75 to 90) μm mesh, was used for sorption experiments of phenol. Alkaline Hydrothermal Treatment of BFA (CZBFA). The dried BFA of 200 μm (100 g) was mixed with 3.01 mol·kg−1 NaOH (Rankem, India, 0.999 mass fraction, A.R grade used as received) solution (1 L) in a 3 L refluxing flask. The admixture was cured for 72 h at 373 ± 5 K. The resultant product was separated and washed off using doubly distilled water until the excess sodium hydroxide was removed. The resultant material (CZBFA) was dehydrated at 373 ± 10 K in hot air oven. The (75 to 90) μm mesh sieved CZBFA was used for the sorption of phenol. The yield of the final product (CZBFA) was about 75 ± 5 %. Fusion Treatment of BFA (FZBFA). The dried BFA of 200 μm was thoroughly mixed and ground with solid sodium hydroxide in a predetermined ratio (NaOH/BFA, 1.2 w/w). The NaOH mixed material was allowed to fuse in stainless steel container at 823 ± 10 K for 1.5 h. The ensuing the material was brought to room temperature ground further and added to 128 mL of doubly distilled water. The resulted suspension was stirred in a conical flask for 12 h. The mixture was then crystallized under static conditions at 363 K for 6 h. The resultant solid was separated by filtration using Whatmann filter paper no. 42. From the solid material, the excess of NaOH was removed by using doubly distilled water. The remaining solid material (FZBFA) was dried at 373 ± 10 K, ground, and (75 to 90) μm mesh sized particles sieved out. The yield of the final product (FZBFA) was about 82 ± 5 %. The dried BFA and zeolitic materials (CZBFA and FZBFA) were stored in airtight desiccators until being utilized for the sorption process. Characterization of Sorbents. The specific surface area and pore volume of the sorbents (BFA, CZBFA, and FZBFA) were determined using Brunauer−Emmett−Teller (BET) and Barrett−Joyner−Halenda (BJH) N2 adsorption and desorption methods at 77 K (Micromeritics Gemini 2360, Shimadzu, Japan). Sorbents were chemically characterized by a X-ray fluorescence technique (X-ray XDL-B, Fischer Scope, Japan). FT-IR spectra were brought by using a Fourier transform infrared (FT-IR) spectrometer (Thermo-Nicolet iS-10, USA). The powder X-ray diffraction (PXRD) patterns of the sorbents were obtained using Panalyticals X-Pert Pro (Netherlands) instrument employing nickel filtered Cu Kα (λ = 1.5406 Å) radiations. The surface morphologies of sorbents were analyzed

qe =

(C0 − Ce) V m

(1)

where C0 is the initial phenol concentration, Ce is the equilibrium phenol concentration, V is the volume of the solution, and m is the mass of the sorbent. Column Study. Column experiments were performed using a (75 to 90) μm mesh size of 1.0 g of sorbent (BFA and CZBFA), filled in glass column (25 × 0.5 cm) with glass wool support. The air entrapment in column was avoided by filling the column using a thick suspension of sorbents with hot water. The known concentration of phenol was passed through the column under gravitational force at a flow rate of 30 mL·h−1. The amount of phenol retained on the column was calculated by checking the concentration of phenol in effluent at the end of the column. The column operation was stopped at about 90 % of the sorption capacity (C/C0 = 0.90). The column technique is mostly dependent on the nature of the breakthrough curves of C/C0 versus time or volume. In most of the cases it was found that it shows an “S” shape breakthrough curves with different break points and sharpness. The breakthrough capacity of the column was determined by loading BFA and CZBFA at pH 2.0 with a 4.26 mmol·kg−1 concentration of phenol using the C/C0 against volume (Ve) plot. Desorption Studies. In the batch desorption study, the unsorbed amount of phenol from the phenol loaded sorbents was eliminated by the gentle wash of doubly distilled water. The loaded sorbents (0.5 g) were resuspended in 50 mL of desorbents, either 0.50 mol·kg−1 NaOH, 0.5 mol·kg−1 HCl, or 6.96 mmol·kg−1 anionic surfactant, sodium dodecyl sulfate (SDS), and equilibrated for 24 h. The percentage of desorption is calculated using eq 2. % desorption = 1438

Cd·Vd × 100 w·qe ·1000

(2)



Article

where, Cd is the desorbed sorbate concentration, Vd is the volume of the desorption solution, and w is the mass of the presorbed sorbent.

with a H4 type of hysteresis loop as per the International Union of Pure and Applied Chemistry (IUPAC). The BET surface area increased significantly after treatment as compared to virgin BFA, FZBFA (465 m2·g−1) > CZBFA (368 m2·g−1) > BFA (46 m2·g−1). The average pore diameter decreased after treatment as compared to BFA (3.38 nm), CBZFA (2.75 nm), and FZBFA (2.83 nm). This confirms the mesoporous structures of the sorbents (BFA > CZBFA > FZBFA). The pHpzc values obtained by the mass titration method are 8.07, 8.61, and 8.67 pH for BFA, CZBFA, and FZBFA, respectively (Figure S2, SI).21 FTIR Analysis. FTIR spectra of BFA and CZBFA were wellcharacterized in our earlier report.22 The data obtained from FTIR spectra of FZBFA (Figure S3, SI) are given in Table 2.

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RESULTS AND DISCUSSION Characterization of Sorbents. The analysis of the physicochemical data (Table 1) reflects that the amounts of Table 1. Physicochemical Properties of BFA, CZBFA, and FZBFA BFA

CZBFA

FZBFA

Proximate Analysis (w/w %) loss on drying 12.56 ± 0.2 15.63 ± 0.2 18.44 ± 0.2 moisture content 11.69 ± 0.3 12.11 ± 0.3 16.18 ± 0.3 ash content 75.84 ± 0.2 70.45 ± 0.2 65.55 ± 0.2 Physicoproperties specific density 1.93 ± 0.02 2.04 ± 0.02 2.15 ± 0.02 bulk density (g·cc−1) 1.75 ± 0.02 1.98 ± 0.02 2.13 ± 0.02 dry density (g·cc−1) 1.16 ± 0.02 1.31 ± 0.02 1.39 ± 0.02 void ratio 0.69 0.56 0.54 porosity (fraction) 0.41 0.36 0.35 pHpzc 8.07 ± 0.05 8.62 ± 0.05 8.67 ± 0.05 N2 Adsorption and Desorption BET and BJH Models BET surface area (m2·g−1) 46 368 465 adsorption average pore 3.38 2.75 2.83 diametera (BET) (nm) t-Plot external surface area (m2·g−1) 24.18 160.12 279.01 micropore area (m2·g−1) 21.42 208.13 185.70 micropore volume (cm3·g−1) 9.75·10−3 9.56·10−2 8.28·10−2 BJH Pore Size Distribution adsorption cumulative surface 18.59 118.00 195.40 area of pores (m2·g−1) desorption cumulative surface 2.35 146.83 261.25 area of pores (m2·g−1) adsorption average pore 7.94 5.73 5.50 diametera (nm) desorption average pore 6.54 4.86 4.57 diametera (nm) 3.85·10−2 2.53·10−1 3.29·10−1 total pore volume (cm3·g−1) Chemical Constituents (w/w %) SiO2 47.44 43.89 44.87 Al2O3 20.46 18.75 19.46 Fe2O3 5.76 3.89 2.89 CaO 5.12 3.12 3.22 MgO 4.59 3.45 4.01 Na2O 4.66 6.79 7.46 K2O 3.45 2.46 2.24 a

Table 2. Comparison of Data Obtained from FTIR Spectra of BFA, CZBFA, and FZBFA wavenumbers cm

−1

3600−3300 1700−1400

1250−850

720−650

420−500

BFA indication silanol (Si−OH) OH− deformation and bending vibration of interstitial water asymmetric stretching of internal tetrahedral TO4 Si−O−Si (TSi, Al) symmetric stretching of internal tetrahedral TO4 (TSi, Al) bending mode of internal tetrahedral TO4 (O-T-O)

−1

cm

CZBFA cm

−1

FZBFA cm−1

3418.83

3421.32 1639.44

3448.01 1651.79 1441.11

1096.34 795.07

1022.33 736.22

981.13 765.92

668.41

685.73

467.30 454.80 439.70

461.73 420.26

463.68 419.67

The shifting of bands mentioned in Table 2 confirms the zeolite formation of aluminosilicates.15,18 The increased amount of tetrahedral sites of the zeolitic aluminosilicate framework can be explained by the decreasing frequency of asymmetric stretching vibration of the tetrahedral.15,18 The band at 609.4 cm−1 in FZBFA can be attributed to the double ring mode of external linkage of the zeolite framework. The banding vibration at 461.73 cm−1 indicates TO4 bending in the internal tetrahedral. The band at 439.70 cm−1 and 420.26 cm−1 could be owing to the pore opening of external linkage of the zeolite framework in CZBFA and FZBFA, respectively. PXRD Analysis. From the PXRD patterns, the crystalline and mineralogical characteristics of sorbents have been obtained using the database provided by the Joint Committee on Powder Diffraction Standards (JCPDS) and the International Centre for Diffraction Data.23,24 The powder X-ray diffraction pattern of BFA (Figure 1) shows the existence of the glass phase.19 BFA exhibits the presence of mainly α-quartz peaks (JCPDS 5-490), mullite (JCPDS 15-0776), and a small peak of stilbite.24 The PXRD pattern of CZBFA exhibits a comparatively flat and low-intensity hump at a low diffraction angle. CZBFA also exhibits several new and sharp diffraction peaks that are not present in PXRD of BFA. The zeolite P (phillipsite, JCPDS 39-0219), analcime (JCPDS 76-0901), and chabazite (JCPDS 12-0194) are positively identified in CZBFA. Phillipsite (P) and analcime (A) zeolites cover the major part of synthesized zeolites with d-spacing values of 6.95, 4.22, 3.74, 3.66, 3.32, 2.89, 2.68, 1.97, 1.89, 1.80, 1.71, and 1.68 and 5.54, 4.82, 3.41, 2.27, 2.22, and 1.74, respectively.25 The newly observed intense

Pore diameter values come from the 4V/A relation.

SiO2, Al2O3, and other oxides except Na2O within zeolites (CZBFA and FZBFA) decreased due to the dissolution into the alkaline solution during alkaline hydrothermal treatment. During the formation of zeolite crystal, the Na ions get captured to balance the negative sites of aluminate; henceforth the amount of Na2O increased in CZBFA and FZBFA. The aluminosilica gel is produced due to the dissolution of glass phase which was a prematerial for the creation of zeolite crystals. The conversion of fly ash into sodium salts of silicate and aluminate is found to be enhanced under alkali fusion. BET N2 adsorption desorption isotherms (Figure S1, Supporting Information, SI) follow mixed I + IIb type of sorption isotherm 1439



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Figure 2. Effect of pH on the uptake of phenol by ■, BFA; ●, CZBFA and ▲, FZBFA (T = 303 K, C0 = 1.07 mmol·kg−1, m = 2 g·L−1).

charge. At a low solution pH, the sorption of phenol is high because of dispersive interactions which are promoted in solutions with pH below the pHpzc of the sorbents. This can be due to the minimization of interaction within the uncharged molecules and charged surface. Sorbents possess a negative charge, and phenol exists mainly as a hydrophilic anionic form in alkaline pH > pHpzc and pKa, respectively.26 This results in the development of a high repulsive force among the phenolate ions and surface as well as within the solute sorbed on the sorbent. Thus, the sorption of phenol by the sorbents is approximated well by its molecular form and dispersive interactions. The sorption efficiency follows the order FZBFA > CZBFA > BFA. The higher sorption capacity of FZBFA compared to CZBFA and BFA in acidic solution is due to the micropore structure of FZBFA, where phenol (molecular dimension 5.76 × 4.17 A°) can be intensively sorbed by a micropore filling mechanism. Effect of Sorbent Dosage and Initial Phenol Concentration. The sorption increases with sorbent dose due to the accessibility of ample unoccupied sorbent sites by phenol molecules. It continues until the sorbent becomes saturated by phenol, then after the removal decreases as the dose concentration is increased, and attains a constant value (Figure 3). With a rise in initial phenol concentration (C0) the amount of phenol per unit weight of sorbent increases because of the high concentration gradient which minimizes the resistance to mass transfer within the sorbate and sorbent interphases (Figure 3) and enriches the interaction between phenol and sorbents.27 The removal of phenol by FZBFA is enhanced as compared to CZBFA and BFA. Effect of Temperature. The sorption of phenol on BFA, CZBFA, and FZBFA increases with a rise in temperature (Figure 4) representing the endothermic nature of sorption due to the diffusion process and breaking of hydrogen bonds.27−29 As the rise in temperature causes more dissociation of the phenol molecules, the mobility of dissociated molecules/ions increases with temperature and decreases retarding forces acting on the diffusing molecule/ions, thereby increasing the sorptive capacity of sorbent. It can also be explained on the basis of hydrogen bonding as phenol possesses appreciable solubility (8.85·10−1 mol·kg−1 at 20 °C) due to hydrogen bonding in aqueous solution. These hydrogen bonds get broken with a

Figure 1. PXRD patterns (intensity I vs 2θ°, X = zeolite X, Z = ZSM 12, L = zeolite A, P = phillipsite, A = analcime, C = chabazite, Q = α-quartz, M = mullite, S = stilbite) and SEM micrographs (500× magnification) of BFA (I), CZBFA (II), and FZBFA (III).

peaks at 2θ = 15.97° and 2θ = 26.13° can indicate the significance of zeolite formation in CZBFA. The hump at the lower diffraction angle is still more suppressed as compared to BFA and CZBFA in the case of FZBFA. Zeolite P and analcime are found to be dominant in zeolite formation during fusion treatment. The other crystalline phases identified in the FZBFA are zeolite A (JCPDS 14-90), zeolite X (JCPDS 28-1036), and ZSM 12, calcined (JCPDS 15274). In the formation of FZBFA it can be presumed that a larger amount of glass phases (quartz and mulite) have reacted in alkaline media during fusion treatment to form sodium silicates and sodium aluminosilicates. Morphology of the Sorbents. The SEM micrograph of BFA (inset, Figure 1) shows fibrous structures along with large irregular shapes and surfaces of silicate masses. The SEM micrograph of CZBFA and FZBFA (inset, Figure 1) display the occurrence of spherical particles. The glass phase characteristic has been decreased due to treatment as shown in X-ray diffraction patterns.24 The SEM photograph of CZBFA exhibits a honeycomb aperture with holes. Its surface shows hollow particles with interior voids and silicate channels. FZBFA demonstrates an analcime type morphology as reported by Lin and Hsi.25 FZBFA also exhibits clustering of the particles. Batch Sorption Studies. Effect of pH. No significant change was observed in the uptake of phenol up to 8.0 pH, and beyond pH 8.0 the uptake dropped down gradually (Figure 2). It can be explained by two factors, pKa of phenol and pHpzc of the sorbents. The pKa of phenol is 9.95, and below that pH phenol exists in the molecular form. The pHpzc of sorbents (BFA, CZBFA, and FZBFA) is between (8.0 to 8.67) ± 0.05 pH, and below this pH sorbents possess a positive surface 1440



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Table 3. Thermodynamic Parameters for the Sorption of Phenol on BFA, CZBFA, and FZBFA −ΔG0/(kJ·mol−1)

ΔH0 −1

sorbent

303 K

313 K

323 K

333 K

kJ·mol

BFA CZBFA FZBFA

4.34 7.44 10.15

4.65 8.16 11.14

5.00 8.74 12.10

5.41 9.20 12.97

6.46 10.36 18.38

ΔS0 −1

J·K ·mol−1 35.57 58.95 94.23

where, Kd is the distribution coefficient, ΔH0 is the change in enthalpy, ΔS0 is the change in entropy, R is the gas constant, and T is the temperature. The negative values of ΔG0 indicate that the sorption process is spontaneous and favorable at higher temperatures. The positive values of ΔH0 varies from (6.48 to 18.38) kJ·mol−1. From the lower value of ΔH0 (< 20 kJ·mol−1), the sorption process can be assumed to be endothermic and physical in nature involving a weak attraction force.29 The positive value of ΔS0 suggests weak interaction between phenol and sorbents with a rise in the degree of freedom. Effect of Contact Time on Sorption. The sorption equilibrium was established within 6 h, and until then sorption arises gradually. After 250 min, considerably no decline in the removal of phenol has been detected (Figure 5). In the

Figure 3. Effect of initial phenol concentration as uptake (m = 2 g·L−1) and sorbent dosage as % removal (C0 = 1.07 mmol·kg−1) of phenol by ■, BFA; ●, CZBFA and ▲, FZBFA (T = 303 K, pH = 2).

Figure 4. Effect of temperature on the uptake of phenol by ■, BFA; ●, CZBFA and ▲, FZBFA (C0 = 1.07 mmol·kg−1, pH = 2, m = 2 g·L−1).

rise in temperature, which makes phenol more insoluble, and so phenol molecules possess a high affinity for a solid surface.28 However, the breaking of hydrogen bonds is an endothermic process which overcomes the exothermic sorption process. It would be also expected that, if the sorption process is controlled by the diffusion process (intraparticle/external pore diffusion), then the sorption capacity rises with the temperature. Similar results have been reported by Mall et al.,27 stating the endothermic nature of the diffusion process. Among the studied sorbents, FZBFA exhibits a higher sorption capacity than CZBFA and BFA due to a large surface area and large pore volume. The efficiency of sorbents for the removal of phenol is FZBFA > CZBFA > BFA. Thermodynamic parameters are evaluated from van't Hoff plots (Figure S4, SI) using different temperatures studied at (303 to 333) K at 10 K intervals. The change of enthalpy (ΔH0) and change of entropy (ΔS0) evaluated using eq 3 and the values obtained are shown in Table 3. R ln Kd =

−ΔG 0 ΔH 0 = ΔS 0 − T T

Figure 5. Effect of contact time on the uptake of phenol by ■, BFA; ●, CZBFA and ▲, FZBFA (C0 = 1.07 mmol·kg−1, T = 303 K, pH = 2, m = 2 g·L−1).

beginning of the sorption process, a high concentration gradient and availability of unoccupied sorbent sites provide the necessary driving force to enhance the sorption rate, so the sorption is fast for an initial 150 min. With sorption time the repulsive force is exerted on the surface of the sorbent due to the accumulation of phenol molecules on the sorbent surface, and further consumption of phenol molecules takes more time. As a result of it the uptake rate becomes slow near equilibrium, and at some point the sorption rate equals the desorption rate. This leads to equilibrium of the sorption system and their removal becomes unchanged with time. The equilibrium sorptive removal follows the order: FZBFA (45.94 mg·g−1) > CZBFA (39.05 mg·g−1) > BFA (24.51 mg·g−1). Kinetics of the Sorption Process. The equilibrium is built up within two interphases, bulk and solid surface, due to sorption and desorption phenomena with time. The sorption

(3) 1441



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Table 4. Kinetic Parameters for the Removal of Phenols by BFA, CZBFA and FZBFA Pseudofirst Order qe mg·g BFA CZBFA FZBFA

kf −1

min−1

R2

−3

10.62 11.07 9.95

6.19·10 7.30·10−3 6.59·10−3

0.9942 0.9900 0.9973

Pseudosecond Order ks

qe mg·g BFA CZBFA FZBFA

−1

h

−1

g·mg ·min

−1

−1

−3

25.60 40.05 46.77

2.41·10 2.66·10−3 3.03·10−3 External Diffusion

mg·g ·min−1

R2

1.58 4.26 6.62

0.9983 0.9994 0.9996

ked BFA CZBFA FZBFA

BFA CZBFA FZBFA

cm·min−1

R2

6.09·10−4 1.66·10−4 2.35·10−4 Intraparticle Diffusion

0.9756 0.9717 0.9937

I1

kid,1

I2

kid,2

mg·g−1

mg·g−1·min−1/2

R2

mg·g−1

mg·g−1·min−1/2

R2

14.55 28.21 36.43

0.643 0.715 0.616

0.9917 0.9905 0.9957

26.14 43.36 45.53

0.127 0.091 0.152

0.9657 0.9785 0.9664

rate is determined by pseudofirst-order rate and pseudosecondorder rate expressions. The pseudofirst-order model is defined as26,30,31 ⎛ k ⎞ log(qe − qt ) = log qe − ⎜ f ⎟ ·t ⎝ 2.303 ⎠

(4)

where, qt is the quantity of phenol sorbed on the surface at time t and kf is the rate constant. The linearity of log (qe − qt) against t plots (Figure S5, SI) with good correlation coefficients shows its applicability for phenol sorption. The values of kf (slope) and qe (intercept) evaluated from the plots are given in Table 4, which suggest a fast interaction between sorbents and phenol molecules. These values indicate that the removal of phenol by the sorbents is rapid. But, the sorption capacity, qe, obtained for the plots did not yield values near to equilibrium values. The values obtained are low as compared to monolayer capacities observed in the Langmuir isotherm model. It suggests that the sorption process does not follow the pseudofirst-order kinetic model. The pseudosecond-order kinetic model can be stated by30,31 t 1 1 = + t 2 qt qe (ks·qe ) (5)

Figure 6. Pseudosecond-order kinetic model for the removal of phenol by ■, BFA; ●, CZBFA and ▲, FZBFA (C0 = 1.07 mmol·kg−1, T = 303 K, pH = 2, m = 2 g·L−1).

kinetics, suggesting a somewhat complex sorption mechanism instead of a single step. Diffusion Studies. Diffusion of sorbate has a significant effect on sorption. Generally, in batch mode sorption experiments, the sorption can be governed by film diffusion and/or intraparticle diffusion processes. Hence, it may be expected that sorption proceeds through one or more than one steps or combination of two steps. The effect of diffusion on sorption was examined using a film and intraparticle diffusion model. The kinetic data are further fitted to the film diffusion model, and ln(Ct/C0) versus time plots (Figure S6, SI) were executed to describe whether the

where ks is the kinetic constant. The plots of t/qt versus t (Figure 6) drawn according to the equation show similar results as observed in the case of sorption of nickel by weathered basaltic andesite material31 where the sorption data were suitably represented by the pseudosecond-order kinetic model. The initial sorption rate, h, is higher for the FZBFA system than that by BFA and CZBFA. It is plausible to conclude that the sorption of phenol onto the sorbents follows pseudosecond-order 1442



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sorption of phenol on sorbent by film diffusion and intraparticle diffusion simultaneously. Further, the slow step presented in Figure 7 signifies the transfer of phenol molecule into macropores/ mesopores and micropores of BFA, CZBFA, and FZBFA.32 Mass Transfer Study. The influence of the solution to solid transport and particle diffusion on the sorption process has been carried out with the help of mass transfer model, suggested by McKay for the determination of the surface mass transfer coefficient, βL.31

sorption proceeds sequentially through the sorbent particle and in the bulk of the solution by diffusion.26,30,31 ⎛C ⎞ ⎛A⎞ ln⎜ t ⎟ = −ked·⎜ ⎟ ·t ⎝V ⎠ ⎝ C0 ⎠

(6)

where ked is external diffusion rate constant, Ct is the concentration at time t, A/V is external sorption area to the total solution volume, and t is time. The regression coefficient, R2 values > 0.9 (Table 4), for all studied systems specifies that the sorption is likely to be a surface phenomenon, taking place on the exterior surface. Thus, for sorption, external diffusion may possess a crucial part. The value of R2 is comparatively lower than intraparticle diffusion, suggesting that both of them have a substantial influence on the sorption process. The influence of diffusion process has been examined by means of a Weber−Morris intraparticle diffusion model.26,27,31 qt = k id·t 1/2 + I

⎡⎛ C ⎞ ⎧ ⎫⎤ 1 ⎬⎥ ln⎢⎜ t ⎟ − ⎨ ⎢⎣⎝ C0 ⎠ ⎩ (1 + mk) ⎭⎥⎦ ⎫ ⎧ (1 + mk) ⎫ ⎧ mk ⎬·βL ·S ·t ⎬−⎨ = ln⎨ ⎭ ⎩ (1 + mk) ⎭ ⎩ mk

(8)

where m is the mass of sorbent per unit volume, k is the equilibrium constant acquired by using Langmuir constants, sorption capacity (qe), and sorption energy (b), βL is the mass transfer coefficient, and S is the outer surface of the sorbent per unit volume of the particle-free slurry.31 The plots of ln[(Ct/C0) − {1/(1 + mk)}] versus t for different temperatures and at different initial concentrations of phenol (Figure S7, a and b, SI) are straight lines, supporting the cogency of McKay model for the sorption. The decrease of uptake of phenol on BFA, CZBFA, and FZBFA can be due to surface saturation with the rise in initial phenol concentration which is represented by the decreased values of βL (Table 5). In temperature studies, the pace of mass transfer becomes rapid with temperature which is confirmed by the higher values of βL at an increased temperature.33 The mixture was stirred continuously, so solution-to-solid transport cannot be considered as a rate-determining step. Thus, diffusion is the key factor in deciding the rate of sorption and indicates that the sorption rate is not only dependent on the mass transfer process.33,34 Rate Expression Model. The overall sorption rate was approximated by using reported models as stated below.31,33

(7)

where kid is the intraparticle diffusion rate constant and I is the intercept. The straight line nature of the plots (qt versus t1/2) without an intercept indicates that the sorption proceeds exclusively by intraparticle diffusion only. But in our observation the effect of thickness of boundary layer has been detected with intercept I, of (14.55 to 45.53) mg·g−1 variation (Table 4). However, data exhibit multilinear plots (Figure 7), indicating the influence of

F=1−

6 π2

∞

∑ n=1

1 exp[−n2Bt ] 2 n

Bt = −0.4977 − ln(1 − F ) Bt =

(9) (10)

π 2Di r2

(11)

where F is the fractional equilibrium attainment at time t, Di is the effective diffusion coefficient of phenol, r is the radius of spherical sorbent particle, n is an integer (1, 2, 3, ..) defining the series obtained for a Fourier type analysis, and B is a time constant. The film diffusion and intraparticle diffusion in sorption process were differentiated by employing the plots of Bt versus t (Figure S8, a and b, SI) at different initial phenol concentrations and different temperatures. The obtained results are similar to our earlier report31 which indicates that the external particle film diffusion is a dominant sorption process.31,33 This assumption was confirmed by drawing the plots of McKay, log(1 − F) versus time (Figure S8, c and d, SI) at different initial phenol concentrations and different temperatures. The resulted plots are linear which signifies that the sorption process is exclusively governed by film diffusion for all studied phenol−sorbent systems.

Figure 7. Intraparticle diffusion plots (qt vs t1/2) of phenol on ■, BFA; ●, CZBFA and ▲, FZBFA (T = 303 K, C0 = 1.07 mmol·kg−1, m = 2 g·L−1).

multiple sorption processes. The first sharp portion can be attributed to film diffusion. The second portion of the plots demonstrates the intraparticle diffusion process which is slow and can be the rate-limiting step of the overall sorption. The values of rate parameter, kid, computed for the first portion of the plots range from (0.62 to 0.72) mg·g−1·min−1/2 for the first portion, while for the second portion it is in the (0.09 to 0.15) mg·g−1·min−1/2 range (Table 4). The pore diffusion nature of phenol sorption from the sorbent surface has been intimated by the higher value of kid,1 than kid,2. This pore diffusion rate reduces with time due to gains in diffusion resistance. It is reasonable to deduce that multiple processes carry on the 1443



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Table 5. Mass Transfer Coefficients (βL) and Effective Diffusion Coefficient Di at Different Initial Phenol Concentrations (C0) and at Different Temperatures for Phenol Sorption by BFA, CZBFA, and FZBFA C0

βL

mmol·kg−1

cm·min−1

R2

−7

BFA

1.07 2.13 3.19

5.99·10 2.87·10−7 1.66·10−7

0.9968 0.9984 0.9934

CZBFA

1.07 2.13 3.19

8.15·10−7 3.43·10−7 2.04·10−7

0.9884 0.9963 0.9935

FZBFA

1.07 2.13 3.19

1.25·10−6 4.19·10−7 2.29·10−7

0.9978 0.9925 0.9871

BFA

CZBFA

FZBFA

BFA

CZBFA

FZBFA

−7

303 313 323 333 303 313 323 333 303 313 323 333

5.93·10 6.02·10−7 6.06·10−7 6.25·10−7 9.40·10−7 1.05·10−6 1.34·10−6 1.62·10−6 1.24·10−6 1.32·10−6 1.41·10−6 1.72·10−6

Di·10−8

mmol·kg−1

cm2·min−1

R2

1.07 2.13 3.19 1.07 2.13 3.19 1.07 2.13 3.19

3.09 2.95 2.77 3.41 3.05 2.76 3.69 3.46 2.96

0.9749 0.9447 0.8605 0.9863 0.9723 0.9923 0.9937 0.9893 0.9875

Di·10−8

K

cm ·min 2

D0·10−7

−1

2.39 2.48 2.80 3.03 2.52 2.87 3.26 3.40 3.34 3.53 3.77 3.96

R

2

0.9795 0.9924 0.9582 0.9907 0.9866 0.9884 0.9981 0.9979 0.9853 0.9746 0.9869 0.9684

The values of Di (Table 5) are computed with eq 12. ln Di = ln D0 −

βL cm·min−1

C0

T 303 313 323 333 303 313 323 333 303 313 323 333

T K

Ea RT

L·min−1

Ea

1.51 1.44 1.35 1.66 1.49 1.34 1.79 1.69 1.44 −ΔS# J·K−1·mol−1

3.64

6.89

58.81

7.88

8.64

52.38

2.23

4.79

62.86

solution. This effect enhances the diffusion of phenol into the cavity of solid from boundary layer. The rise in temperature enhances the mobility of phenol molecules; hence a large number of phenol molecules have sufficient energy to access the active sites of surface and also decrease the retarding force which results in the gain of Di value. Thus, the value of Di in the sorption process is affected by two processes. Diffusion becomes rapid for widen pores due to less resistance to mass transport, while it slows down for narrower pores owing to the strong resistance exerted within the sorbents surface. The negative value of ΔS# reflects that the sorption of phenol does not cause any internal change in sorbent. These studies justify the participation of diffusion processes during the sorption of phenol. Sorption Equilibrium Isotherms. The efficiency and nature of the sorption on the sorbent can be evaluated from the sorption isotherms. The experimental data of phenol sorption are furnished for the linearized isotherms equations of the Langmuir,35 Freundlich,35 Dubinin−Radushkevich (D-R),36

(12)

The activation energy, Ea, and the pre-exponential constant analogous to the Arrhenius frequency factor, D0, are calculated from linear plots of ln Di versus 1/T (Figure S8b, SI) using the slope and intercept, respectively. The entropy of the activation ΔS# is computed using obtained D0 values (Table 5). ⎛ k T ⎞ ⎡ ΔS # ⎤ ln D0 = ln 2.72 + ln d 2 + ln⎜ B ⎟ + ⎢ ⎥ ⎝ h ⎠ ⎣ R ⎦

0.9969 0.9938 0.9919 0.9945 0.9903 0.9681 0.9629 0.9762 0.9902 0.9934 0.9905 0.9732 B·10−2

kJ·mol−1

cm ·min 2

−1

R2

(13)

where kB is Boltzmann constant, h is the Planck's constant, R is the gas constant, T is temperature, and d is the spacing within the active sorbent site (0.5·10−8 cm). The results reveal that the value of Di (Table 5) decreases significantly with the rise in initial phenol concentration due to reduction of phenol diffusion into the boundary layer from the 1444



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Table 6. Isotherm Parameters of Phenol Sorption by BFA, CZBFA, and FZBA qm

b

Langmuir

mg·g−1

L·mg−1

RL

R2

SSE

SAE

ARE

ARS

HYBRID

MPSD

BFA CZBFA FZBFA

47.19 69.25 77.28 Kf

0.046 0.045 0.224

0.067 0.068 0.015

0.9949 0.9973 0.9974

1105.67 780.89 138.97

69.25 59.21 19.82

0.45 0.21 0.06

0.56 0.26 0.09

1236.83 477.43 67.3

72.71 15.24 1.7

Freundlich

L·g−1

n

R2

SSE

SAE

ARE

ARS

HYBRID

MPSD

BFA CZBFA FZBFA

10.74 10.42 31.77

3.75 2.76 5.45

0.9797 0.9676 0.9472 E

2700.39 1111.97 8690.34

113 234.95 207.73

0.67 0.82 0.57

0.75 0.91 0.63

2567.7 6411.64 3929.03

130.25 193.01 92.5

Xm

β

D-R

mg·g−1

mol2·J−2

kJ·mol−1

R2

SSE

SAE

ARE

ARS

HYBRID

MPSD

BFA CZBFA FZBFA

18.97 35.41 44.51 KT

9.80·10−5 6.87·10−6 2.97·10−7

0.755 0.698 1.297

0.9965 0.9394 0.8814

1179.07 2499.62 4209.03

71.85 110 144.03

0.42 0.38 0.39

0.48 0.43 0.44

1615.8 2135.1 2845.05

64.2 51.79 54.5

Temkin

L·mg−1

B1

R2

SSE

SAE

ARE

ARS

HYBRID

MPSD

BFA CZBFA FZBFA

8.06 13.96 10.99

1.042 0.539 8.238

0.9706 0.9854 0.9676

3341.99 9518.92 19482.85

126.4 217.25 311.63

0.75 0.76 0.85

0.84 0.85 0.95

3202.88 5486.46 8831.06

163.75 164.91 208.46

and Temkin37 models. The sorption quantity qe (mg·g−1) distributed at equilibrium was measured with the aid of phenol concentration. All values of R2 in Table 6 are closer to unity (> 0.9) which demonstrates a heterogeneous nature of sorption on sorbents. The Langmuir isotherm plots of Ce/qe against Ce are linear with highly significant regression coefficient values closer to unity (Table 6) than other isotherm equations indicating that sorption can be well explained by the Langmuir isotherm model. The small values of dimensionless parameter, RL (< 1), manifest that the sorption is favorable under the applied conditions. The lesser RL values for FZBFA than CZBFA and BFA exhibit a higher tendency of phenol sorption. The Langmuir monolayer sorption capacity of the sorbents follows the order: FZBFA (77.28 mg·g−1) > CZBFA (69.25 mg·g−1) > BFA (47.19 mg·g−1). The obtained values are higher than those found for activated carbon (43.290 mg·g−1) and rice husk (14.35 mg·g−1) accounted by Anirudhan et al.34 and Shiundu et al.37 The Freundlich isotherm plots of ln qe versus ln Ce are linear with the intercept of multilayer sorption capacity, Kf, varying from (10.74 to 31.77) L·g−1 (Table 6). The values of heterogeneity factor, n, obtained from the slope are greater than one which supports the existence of the multilayer effect on the sorbent surface during the sorption. The higher value of n for FZBFA than BFA and CZBFA demonstrates the higher sorption of phenol on FZBFA with the multifaceted sorption process, but the regression coefficient is lower than the Langmuir model. This observation demonstrates the molecular interaction of phenol with subsequent aggregation in the surface monolayer. The pore filling mechanism is tested with the help of the D-R isotherm model. The slope and intercept of plots ln qe versus ε2 provide the values of energy constant, β, and sorption capacity, Xm, respectively (Table 6). The ion-exchange and physical nature of sorption process are differentiated from the value of sorption energy, E. The sorption is approximated by the ion-exchange (chemisorption) phenomenon for the value of E within (8 to 16) kJ·mol−1, and the value of E less than

8 kJ·mol−1 designates the physical sorption.38 The physisorption process has been identified in our study as the sorption energy found below 8 kJ·mol−1 (Table 6). The sorption capacity of the D-R isotherm is comparatively low than the Langmuir isotherm (Xm < qm). Temkin parameters are obtained using the plots of qe versus ln Ce (Table 6). The regression constant is higher for CZBFA than BFA and FZBFA which suggest that, as soon as sorbent is covered with sorbate molecules, the sorption heat decreases in the layers. Thus, it shows that the sorption binding energies are uniformly distributed on the surface of CZBFA. The confirmation of the best-fitting isotherm has been done by using error function analysis and the correlation coefficient (R2).39,40 The values of errors, namely, the sum of the squares of the errors (SSE), sum of the absolute errors (SAE), average relative errors (ARE), average relative standard errors (ARS), hybrid fractional error function (HYBRID), and Marquardt's percent standard deviation (MPSD), obtained by evaluating their linear equations (Supporting Information) are mentioned in Table 6. The analysis of errors exhibits that the experimental data are in good agreement with the Langmuir isotherm due to its lower value for SSE, SAE, ARE, ARS, HYBRID, and MPSD errors and higher regression constant R2, while the Temkin, D-R, and Freundlich isotherms poorly describe the experimental data. Column Designing. Fixed-bed column operations have a distinct advantage over batch-mode operations. In this technique the sorbent and sorbate interaction remains uninterrupted by incoming fresh sorbate solution. The column study with FZBFA for phenol removal was not feasible as the column got chocked within half an hour. Thus column studies are carried out only with BFA and CZBFA. The breakthrough point is selected indiscriminately at a low value Cb ∼ 0.02 (break point concentration of effluent). Cx is the exhaustion point concentration, closely approaching C0 (influent concentration), at which the sorbent is fundamentally exhausted. C and Ve are given in mass units to elucidate the mass balance in column sorption.41,42 1445



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Table 8. Batch Sorption Capacity (A), Breakthrough Capacity (B), Exhaustion Capacity (C), and Percent of DCU (D) of BFA and CZBFA for Phenol

The values of Cx, Cb, Vb (effluent volume corresponding to Cb), and Vx (volume of effluent corresponding to Cx) are obtained from the breakthrough curve (C/C0 against total quantity of phenol effluent solution, Ve) of phenol sorption on BFA and CZBFA (Figure 8). The total time (tx) taken for the formation of

A mg·g BFA CZBFA

primary sorption zone (PSZ = δ), time required for initial formation of PSZ (tf), time required for the downward movement of PSZ (tδ), fractional capacity (f), mass flow rate (Fm), and degree of column utilization (DCU) at breakpoint are evaluated using breakthrough curves (Table 7) with the aid of reported equations.41,42 The percentage saturation of the column is obtained by eq 14. D + δ(f − 1) ·100 D

47.19 69.25

mg·g

C −1

mg·g

29.64 38.73

D −1

%

47.46 69.24

62.45 55.92

the usage of column capacity. Further, it may be argued that phenol, having a high solubility, possesses more tendencies to remain in the solution and hence it requires longer time for equilibration. The DCU values are 62.45 % and 55.92 % for BFA and CZBFA, respectively. Thus, the results are in good agreement for the removal of phenol from wastewater by the sorbents on column. The resulted parameters provide necessary data to design the fixed bed column for the successful utilization of sorbent capacities at a given condition. Thus, it may enhance the possibility of adopting the technique to treat the known concentration of phenol at a large scale. Desorption Studies. A desorption study was carried out with 0.5 M HCl, 0.5 M NaOH, and 6.96 mmol·kg−1 SDS. It exhibits that 20.46 %, 15.33 %, and 12.93 % phenol is desorbed by 0.5 mol·kg−1 HCl and 21.98 %, 19.45 %, and 15.86 % by SDS from BFA, CZBFA, and FZBFA, respectively. The maximum desorption of 84.99 %, 80.02 %, and 77.91 % is obtained with 0.5 mol·kg−1 NaOH from BFA, CZBFA, and FZBFA, respectively. This can be due to the formation of highly water-soluble sodium phenolates which are readily desorbed from the sorbents.34 The desorption of phenol from saturated column was executed by 0.5 mol·kg−1 NaOH (flow rate of 1 mL·min−1). For column desorption, the exhausted column is washed with doubly distilled water (25 mL) to take out unsorbed phenol. The negligible amount of phenol is observed in washing effluent. After washing, 0.5 mol·kg−1 NaOH is percolated through the column, collected in 10 mL fractions from which the desorbed amount of phenol is measured. The breakthrough curves and desorption curves have been utilized for the computation of the efficiency of solute recovery (Figure 8). From the desorption plots, it is clear that the first 10 mL fraction elutes more than 50 % of phenol and the rest required further treatment of nine fractions of 10 mL which gives about 98 % overall percentage recovery from BFA and CZBFA fixedbed columns. These desorption studies indicate that about 110 mL of 0.5 M NaOH can satisfactorily desorb the phenol from the sorbent. Economic Evaluation. The economic treatment of wastewater is a big demand of growing countries like India which mainly uses low-cost sorbents as an alternative of activated carbons. In India, the cheapest commercial activated carbon used for effluent treatment is available at approximately (600 to 2000)

Figure 8. Breakthrough curves (■, BFA and ●, CZBFA) and % desorption plots (□, BFA and ○, CZBFA) of phenol.

% saturation =

B −1

(14)

The surplus amount of sorbate loaded per unit crosssectional area in a given bed is (Vx − Vb) = (305.73 and 366.88) mg·cm−2 for BFA and CZBFA, respectively, which provide information on the exhaustion capacity of sorbents. The traveling time of PSZ up to the end and out of the column are (420 and 560) min on BFA and CZBFA. The time of establishment of the primary sorption zone (tf) is (1.5 and 2.17) h for BFA and CZBFA, respectively. The fractional capacity f to carry on the removal of phenol on column is 0.7 (BFA) and 0.64 (CZBFA). The percentage saturation at breakpoint computed using f and δ is 72.72 for BFA and 69.77 for CZBFA. The exhaustion capacities were higher than the batch sorption capacities, while breakthrough capacities were lower than batch capacities (Table 8). Thus, because of continuous movement of phenol solution in the column, the available interaction time with sorbent is small which constrains

Table 7. Parameters of the Fixed-Bed Column Design Obtained from the Breakthrough Curve C0 mg·cm BFA CZBFA BFA CZBFA

Cx −3

mg·cm

Cb −3

mg·cm

Vx −3

mg·cm

0.4 0.4 tx/min

0.380 0.395 tδ/min

0.019 0.022 tf/min

428.03 570.70 D/cm

420 560

300 360

90 130

12 12 1446

Vx − Vb

Vb −2

mg·cm

−2

−2

mg·cm

122.29 203.82 δ

305.73 366.88 F

10.91 10.05

0.70 0.64

Fm mg·cm−2·min−1 1.02 1.02 % saturation 72.72 69.77



Article

US dollars per tonnes.29 The bagasse fly ash is available at 25 US dollars per tonnes. The cost of synthesized zeolite CZBFA and FZBFA is estimated to be (150 to 180) US dollars per tonnes including all of the cost. Since the raw material of the sorbent is available easily and the cost of CBZFA and FZBFA is small as compared to activated carbons of cheapest variety, this permits their applicability for the treatment of phenolic wastewater.

(5) WHO. Guidelines for drinking water quality; World Health Organization: Geneva, 1984; Vol. 1, p 85. (6) Nicell, J. A.; Bewtra, J. K.; Biswas, N.; Taylor, E. Reactor development for peroxidase catalyzed polymerization and precipitation of phenols from wastewater. Water Res. 1993, 27, 1629−1639. (7) Lea, J.; Adesina, A. A. Oxidative degradation of 4-nitrophenol in UV illuminated titania suspension. J. Chem. Technol. Biotechnol. 2001, 76 (8), 803−810. (8) Oprea, F.; Sandulescu, M. Phenol removal from wastewater and sour water using ion exchange adsorption. Environ. Eng. Manage. J. 2006, 5, 1051−1058. (9) Mohan, J.; Prakash, R.; Behari, J. R. Electrochemical detection and catalytic oxidation of phenolic compounds over nickel complex modified graphite electrode. Appl. Ecol. Environ. Res. 2004, 2, 25−33. (10) Goncharuk, V. V.; Kucheruk, D. D.; Kochkodan, V. M.; Badekha, V. P. Removal of organic substances from aqueous solutions by reagent enhanced reverse osmosis. Desalination 2002, 143, 45−51. (11) Minamidate, W.; Tokumura, M.; Tawfeek Znad, H.; Kawase, Y. Photodegradation of o-cresol in water by the H2O2/UV process. J. Environ. Sci. Health, Part A 2006, 4, 1543−1558. (12) Sheejan, R. Y.; Murugesan, T. Studies on biodegradation of phenol using response surface methodology. J. Chem. Technol. Biotechnol. 2002, 77, 1219−1230. (13) Radeke, K. H.; Loseh, D.; Struve, K.; Weiss, E. Comparing adsorption of phenol from aqueous solution onto silica fangasite, activated carbon and polymeric resin. Zeolites 1993, 13, 69−70. (14) Murayama, N.; Yamamoto, N.; Shibata, J. Mechanism of zeolite synthesis from coal fly ash by alkali hydrothermal reaction. Int. J. Miner. Process. 2002, 64, 1−17. (15) Wang, Y.; Guo, Y.; Yang, Z.; Cai, H.; Xavier, Q. Synthesis of zeolites using fly ash and their application in removing heavy metals from water. Sci. China, Ser. D 2003, 46, 967−976. (16) Fukui, K.; Katoh, M.; Yamamoto, T.; Yoshida, H. Utilization of NaCl for phillipsite synthesis from fly ash by hydrothermal treatment with microwave heating. Adv. Powder Technol. 2009, 20, 35−40. (17) Wang, S.; Soudi, M.; Li, L.; Zhu, Z. H. Coal ash conversion into effective adsorbents for removal of heavy metals and dyes from wastewater. J. Hazard. Mater. 2006, 133, 243−251. (18) Vucinic, D.; Miljanovic, I.; Rosic, A.; Lazic, P. Effect of Na2O/ SiO2 mole ratio on the crystal type of zeolite synthesized from coal fly ash. J. Serb. Chem. Soc. 2003, 68, 471−478. (19) Inada, M.; Tsujimoto, H.; Eguchi, Y.; Enomoto, N.; Hojo, J. Microwave-assisted zeolite syntheses from coal fly ash in hydrothermal process. Fuel 2005, 84, 1482−1486. (20) Shah, B. A.; Patel, H. D.; Shah, A. V. Equilibrium and kinetic studies of the adsorption of basic dye from aqueous solutions by zeolite synthesized from bagasse fly ash. Environ. Prog. Sustainable Energy 2011, 30, 549−557. (21) Noh, J. S.; Schwarz, J. A. Estimation of the point of zero charge of simple oxides by mass titration. J. Colloid Interface Sci. 1989, 130, 157−164. (22) Shah, B. A.; Mistry, C. B.; Tailor, R. V.; Shah, A. V.; Patel, H. D. Surface modified bagasse fly ash zeolites for the removal of reactive black-5. J. Dispersion Sci. Technol. 2011, 32, 1247−1255. (23) Index (Inorganic to the powder diffraction file, Publication PDIS211; Joint committee on powder diffraction standards: Newton Square, PA, 1971. (24) Treacy, M. M. J.; Higgins, J. B. Collection of simulated XRD powder patterns for zeolites, 4th revised ed.; published on behalf of the Structure Commission of the International Zeolite Association; Elsevier: New York, 2001. (25) Lin, C.-F.; Hsi, H.-C. Resource recovery of waste fly ash: synthesis of zeolite-like materials. Environ. Sci. Technol. 1995, 29, 1109−1117. (26) Ahmaruzzaman, M.; Laxmi, G. S. Activated tea waste as a potential low-cost adsorbent for the removal of p-nitrophenol from wastewater. J. Chem. Eng. Data 2010, 55, 4614−4623. (27) Mall, I. D.; Srivastava, V. C.; Swamy, M. M.; Prasad, B.; Mishra, I. M. Adsorptive removal of phenol by bagasse fly ash and activated

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CONCLUSION The study reveals that BFA is successfully converted into zeolitic material, CZBFA and FZBFA, by hydrothermal and fusion methods. FTIR, PXRD, SEM, and XRF analyses of BFA, CZBFA, and FZBFA data express the distinctness of sorbents and have different characteristics with improved morphology. The sorption capacity of sorbents is examined by batch and column studies with simulated water. The optimized pH is 2.0 for the sorption of phenols. The spontaneous and endothermic nature of the phenol sorption is confirmed by thermodynamics studies. The kinetics of the sorption process is governed by a pseudosecond-order mechanism. The uptake phenomenon of phenol undergoes the external (bulk to solid surface mass transfer) and intraparticle diffusion processes. The applicability of the Langmuir isotherm to the equilibrium data represents the homogeneous sorption site on BFA, CZBFA, and FZBFA. CZBFA and FZBFA showed a higher sorption capacity for phenol as compared to that of BFA. The fine particle size of FZBFA prevented the column study. The breakthrough capacities of BFA and CZBFA were lower than the batch operation. The successive desorption of phenol has been accomplished with 0.5 mol·kg−1 NaOH. The conversion of BFA into zeolitic material provides an economical alternative for the sequestration of phenol from water.

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ASSOCIATED CONTENT

S Supporting Information *

Extensive figures and analytical and spectral characterization of materials. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Funding

The authors are grateful to the SAP meritorious fellowship, UGC, New Delhi, India. Notes

The authors declare no competing financial interest.

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REFERENCES

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