Removal of Rhodamine B, Fast Green, and ... - ACS Publications

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Ind. Eng. Chem. Res. 2004, 43, 1740-1747

Removal of Rhodamine B, Fast Green, and Methylene Blue from Wastewater Using Red Mud, an Aluminum Industry Waste V. K. Gupta,*,† Suhas,† Imran Ali,‡ and V. K. Saini† Department of Chemistry, Indian Institute of Technology, Roorkee, Roorkee 247 667, India, and National Institute of Hydrology, Roorkee 247 667, India

Successful removal of rhodamine B, fast green, and methylene blue from wastewater was achieved using red mud, an aluminum industry waste. The percentage removals of rhodamine B, fast green, and methylene blue on this adsorbent were 92.5, 94.0, and 75.0, respectively. Studies were conducted to delineate the effects of initial absorbate concentration, pH, adsorbent dose, contact time, temperature, and adsorbent particle size. Up to 95-97% removals of rhodamine B, fast green, and methylene blue were achieved in column experiments at a flow rate of 0.5 mL/min. The adsorption was found to be exothermic in nature. The developed system is very useful, rapid, and reproducible for the removal of the three dyes. Introduction Among the various dyes, methylene blue, rhodamine B, and fast green are the most commonly used coloring agents. Methylene blue is an important basic dye widely used for printing calico, dyeing, printing cotton and tannin, indicating oxidation-reduction, and dyeing leather, and in purified zinc-free form, it is used as an antiseptic and for other medicinal purposes. Rhodamine B has moderate wash and light fastness properties on wool. It is also a useful analytical reagent for the detection and determination of metals. However, the use of rhodamine B as a food color has been discontinued for a number of years on account of its suspected carcinogenic nature. Fast green is also a suspected cancer agent.1 Therefore, the removal of these dyes from wastewater is of great concern. Many methods are available for the removal of pollutants from water, the most important of which are reverse osmosis, ion exchange, precipitation, and adsorption. Among these methods, adsorption is by far the most versatile and widely used method for the removal of toxic pollutants2-4 because of its inexpensive nature and ease of operation. A number of workers have used different materials as adsorbents for the removal of different pollutants.5-13 Activated carbon has been used frequently for the removal of various dyes from wastewater for more than three decades,4,14 but it is very costly, and in recent years, the search for the generation of low-cost adsorbents has grown.5 In the present studies, attempts have been made to develop a low-cost adsorbent using red mud, an aluminum industry waste, for the removal of rhodamine B, fast green, and methylene blue from wastewater. The results of these findings are discussed herein. Experimental Section All chemicals and reagents used were of analytical grade and were procured from E. Merck, Mumbai, India. A pH meter (Hach, Loveland, CO) was used to measure * To whom correspondence should be addressed. Tel.: 00911332-285801. Fax: 0091-1332-273560. E-mail: vinodfcy@ iitr.ernet.in. † Indian Institute of Technology, Roorkee. ‡ National Institute of Hydrology.

the pH’s of the solutions. X-ray measurements were carried out on a Phillips X-ray diffractometer employing nickel-filtered Cu KR radiation. The surface area of the adsorbent was measured by a surface area analyzer (model QS-7, Quantasorb surface area analyzer). IR spectra of the sample were recorded on an infrared spectrophotometer (FTIR Perkin-Elmer 1600). The constituents of the prepared adsorbent were analyzed following the routine standard methods of chemical analysis.15 The concentrations of rhodamine B, fast green, and methylene blue were determined using a UV-visible spectrometer (Shimadzu 1601). Material Development. Red mud was obtained from Hindustan Aluminum Company (HINDALCO), Renukoot, India, and it was in the form of a clay-type waste residue composed of a fine fraction (mud) and a relatively coarse fraction (sand) with small granules. The material in the crude form showed poor adsorption properties. Therefore, the material was first treated with hydrogen peroxide at room temperature for 24 h to oxidize adhering organic matter and washed repeatedly with doubly distilled water. The resulting material was dried at 100 °C, cooled, and activated in a muffle furnace at 500 °C for 3 h. The resulting product exhibited an optimum surface area with the best adsorption capacity. The product obtained at temperatures higher than 500 °C had a poor adsorption capacity probably because of the collapse of surface functional groups on the adsorbent. Therefore, the optimization of activation conditions was carried out very carefully. The activated red mud was crushed into smaller particles and sieved to obtain particles of sizes 100-150, 150200, and 200-250 BSS mesh. Finally, the product was stored in a vacuum desiccator until required for use. Adsorption Studies. Batch experiments were carried out using a series of Erlenmeyer flasks of 50-mL capacity covered with Teflon sheets to prevent the introduction of any foreign particle contamination. The effects of pH, concentration, dose, temperature, and shaking time were studied. Isotherms were run by taking different concentrations of rhodamine B, fast green, and methylene blue at the desired temperature and pH. After the required experimentation was over, the solutions were centrifuged, and the concentrations of rhodamine B, fast green, and methylene blue in the

10.1021/ie034218g CCC: $27.50 © 2004 American Chemical Society Published on Web 03/02/2004

Ind. Eng. Chem. Res., Vol. 43, No. 7, 2004 1741

Figure 1. SEM images of activated red mud at different magnifications (a) 5000×, (b) 2500×, (c) 160×, and (d) 80× magnification.

supernatant were determined using a UV-visible spectrometer. Kinetic Studies. For kinetic studies, the batch technique was used because of its simplicity. A series of Erlenmeyer flasks of 50-mL capacity containing a definite volume of solutions of rhodamine B, fast green, and methylene blue of known concentrations were kept in a thermostatic shaking water bath. After the desired temperature had been attained, a known amount of the adsorbent was added to each flask, and the flasks were agitated mechanically. At given time intervals, the solutions were centrifuged, and the supernatants were analyzed for rhodamine B, fast green, and methylene blue as mentioned above. Column Studies. Column studies were carried out using a Pyrex glass column (30 cm × 2 cm). The column on the right-hand side was attached to a manometer by two pressure points to monitor the introduction of air into the column, if any. A wire gauge was fitted at the pressure points to prevent the entry of adsorbent particles into these points. The upper end of the column was covered with a cover containing a tube connection to remove air bubbles. The upper end was also attached to a head tank from which the flow of wastewater was regulated. The flow of wastewater was also controlled by a stopper point at the lower end of the column. For packing of the column, the supporting medium, glass wool, was packed by hydraulic filling. The weighed adsorbent material was kept for 12 h in doubly distilled water, and then it was used to pack the column. The column was kept undisturbed overnight to allow full settlement and saturation to occur. The flow rate was varied to achieve the maximum uptake of rhodamine B, fast green, and methylene blue by this fabricated column. The column runs were carried out until the breakthrough capacity had been consumed. Results and Discussion Characterization of Adsorbent Material. Activated red mud (1.0 g) was stirred with doubly distilled

water (100 mL, pH 6.8) for 2 h and left for 24 h, and an increase in the pH of the water to 7.5 was observed. Activated red mud was found to be stable in water, salt solutions, dilute acids, dilute bases, and organic solvent at temperatures of 30-50 °C and in the pH range of 1.0-10.0. The composition (w/w) of the red mud determined by chemical analysis was found to be 38.80% Fe2O3, 18.80% TiO2, 9.64% SiO2, 17.28% Al2O3, and 6.86% Na2O. The loss on ignition was found to be 7.34%. The density and porosity were found to be 2.0 g/cm3 and 0.45% fraction, respectively. The d-spacing values from X-ray diffraction suggested the presence of hematite, cancrinite, geothite, rutile, anataze, and quartz. The surface area of the adsorbent as calculated by the Brunauer-Emmett-Teller method was 108 m2/g. Scanning electron micrography (SEM) images of the activated red mud (Figure 1) clearly indicate the surface texture and porosity of the material, with a texture similar to aluminum silicates distributed with heavy constituents such as iron. Adsorption Studies. Red mud, an aluminum industry waste, was activated and used as an adsorbent for the removal of three dyes, viz, rhodamine B, fast green, and methylene blue. Effects of parameters such as adsorbate concentration, pH, adsorbent dose, contact time, temperature, and particle size of adsorbent were studied. The effects of cationic and anionic surfactants (cetyltrimethylammonium bromide and manoxol 1B, respectively) on the removal of these dyes were also studied. Effect of the Concentration of the Adsorbates. The uptake of dyes on red mud was studied at initial concentration ranges of (0.1-1.2) × 10-4 M for rhodamine B, (0.1-1.0) × 10-4 M for fast green, and (0.1-1.1) × 10-3 M for methylene blue. Sorption studies were undertaken at three different temperatures, and the amounts of dyes adsorbed at equilibrium against initial concentration were plotted; the resulting plots for rhodamine B are shown in Figure 2. Similar plots were also obtained for other two dyes. The plots for rhodamine B (Figure 2) show that the adsorption of this dye is

1742 Ind. Eng. Chem. Res., Vol. 43, No. 7, 2004

Figure 4. Effect of adsorbent dose on the adsorption of rhodamine B on red mud.

Figure 2. Effect of concentration on the uptake of rhodamine B.

Figure 3. Effect of pH on the percent adsorption of rhodamine B, fast green, and methylene blue.

92.5% at lower concentrations (e1.0 × 10-5 M), decreases to 75.2% at higher concentration (1.0 × 10-4 M), and finally becomes constant. In the case of fast green (figure not shown), removal was nearly 94.0% at concentrations of e1.0 × 10-5 M. Further, the adsorption of fast green decreased to 71.1% at higher concentration (1.0 × 10-4 M). Similarly, the uptake of methylene blue (figure not shown) on red mud was 75.0% at lower concentration (1.0 × 10-4 M) and decreased with increasing concentration. These findings suggest the efficacy of the adsorbent material for the removal of these dyes from aqueous solutions. Effect of pH. The variation in the adsorption of the dyes was studied in the pH range 1-10, and the results are shown in Figure 3. It is clear from the plots that the pH values for optimum removal are 1.0, 7.0, and 8.0 for rhodamine B, fast green, and methylene blue, respectively. The variation of adsorption with pH can be explained by considering the differences in the structures of the dyes, as well as the zero point of charge (ZPC) of red mud. The main constituents of red mud are silica and Fe2O3. The ZPC of SiO2 is ∼2.3, and that of Fe2O3 is ∼8.6. The composite ZPC of the adsorbent was found to be 3.2. Thus, below pH 3.2, the surface has a high positive charge density, and under these

conditions, the uptake of positively charged methylene blue would be low. With increasing pH, i.e., beyond the ZPC, the negative charge density on the surface of the adsorbent increases, resulting in an enhancement in the removal of methylene blue. In the case of rhodamine B, the uptake decreases at pH > 1.0 because of the presence of an acidic group in the dye that dissociates with increasing pH, giving rise to a negative charge on the dye molecule. The higher adsorption of fast green on red mud at high pH can be attributed to the neutralization of surface charge on the red mud through an interaction with OH- ions. This leads to the adsorption of negatively charged fast green dye at higher pH. These findings are also supported by considering the composition of red mud: the planar surface has a negative double layer, but at thebroken edges,16 the polarity of the double layer is reversed, i.e., the fixed part of the double layer is positive and the counterions are anions. The positive double layer at the broken edges changes polarity with increasing pH and results in an enhancement in the number of negative adsorption sites at higher pH. Effect of Adsorbent Dose. The variation of the uptake of the dyes with varying amount of red mud was studied, and the results of this study are shown for rhodamine B in Figure 4. The uptake increases with increasing adsorbent dose. In the case of rhodamine B, the uptake increased by 17.5% when the quantity of adsorbent used was doubled, i.e., from 5.0 to 10.0 g/L. As the amount of red mud was increased further to 20.0 g/L, the uptake increased by only 4.4%. As such, 10.0 g/L of adsorbent was considered to be quite appropriate. For fast green, the adsorption increased by 40.4% when the amount of adsorbent was increased from 5.0 to 10.0 g/L. Upon further increase in the quantity of adsorbent to 20.0 g/L, the enhancement in fast green uptake was only 14.2%. In the case of methylene blue, the uptake increased to 59.5% when the red mud dose was increased from 5.0 g/L to 10.0 g/L. Increasing the adsorbent dose to 20.0 g/L raised the removal by only 9.5%. Thus, 10.0 g/L of red mud seems to be the optimum amount for the removal of all three dyes, and this dose was used in all subsequent experiments performed. Effect of Contact Time. The effect of contact time on the adsorptions of rhodamine B, fast green, and methylene blue was also studied for different particle sizes, i.e., 100-150, 150-200, and 200-250 BSS mesh, and the results for rhodamine B are shown in Figure 5.

Ind. Eng. Chem. Res., Vol. 43, No. 7, 2004 1743

Figure 5. Effect of contact time on the adsorption of rhodamine B on red mud (pH 1).

Figure 6. Effect of temperature on the adsorption of rhodamine B on red mud (pH 1).

The results indicate that equilibrium was achieved in 3, 7, and 8 h for rhodamine B, fast green, and methylene blue, respectively. Further, the results show that the rates of uptake of all three dyes are rapid in the beginning and that 50% of the ultimate adsorption occurs within the first hour of contact. Effect of Temperature. To determine the effect of temperature, adsorption studies of rhodamine B, fast green, and methylene blue were performed at three different temperatures, i.e., 30, 40, and 50 °C, and the results for rhodamine B are shown in Figure 6. Similar plots were observed for the other two dyes. Figure 6 indicates that the adsorption decreases with increasing temperature. The decrease in adsorption with increasing temperature indicates that the process of removal of all three dyes on red mud is exothermic in nature. Effect of Particle Size. The uptakes of rhodamine B, fast green, and methylene blue were studied using red mud of different particle sizes, i.e., 100-150, 150200, and 200-250 BSS mesh (0.112, 0.089, and 0.067 mm, respectively). The plots obtained for rhodamine B are shown in Figure 7, and it can be seen from this figure that the removal improved as the particle size decreased. This is because the smaller particles have more surface area and access to the particle pores is

Figure 7. Effect of particle size on the adsorption of rhodamine B on red mud.

facilitated when their size is small. Similar observations were made for the other two dyes as well (figures not shown). For further adsorption studies, however, a uniform particle size of 150-200 BSS mesh was used because the increase in adsorption upon use of 200-250mesh particles was insignificant. Competitive Adsorption. Wastewater can contain many contaminants, and the presence of surfactants is most likely to be encountered in various situations in dye-bearing wastewaters. The uptake of dyes in the presence of cationic and anionic surfactants [cetyltrimethylammonium bromide (CTAB) and manoxol 1B, respectively] was, therefore, also studied. A decrease in the adsorption of the dyes in the presence of different concentrations of surfactants was observed. It was observed that the uptake of rhodamine B and fast green was affected even at lower concentrations of CTAB and manoxol 1B, whereas in the case of methylene blue, a decrease in the percent adsorption of the dye was observed only at higher concentrations (∼10-6 M) of CTAB and manoxol 1B. Adsorption Models. To determine the mechanistic parameters associated with rhodamine B, fast green, and methylene blue adsorption, the results of the adsorption experiments were analyzed according to the well-known models of Langmuir and Freundlich. Langmuir Isotherm. The Langmuir isotherm has been used by various researchers to study the sorption of a variety of compounds. The model assumes uniform energies of adsorption onto the surface and no transmigration of adsorbate in the plane of the surface. The linear form of the Langmuir isotherm is as follows

1 1 1 ) + qe Q0 bQ0Ce

(1)

where qe is the amount adsorbed (mg/g); Ce is the equilibrium concentration of the adsorbate (mg/L); and Q0 and b are Langmuir constants related to the maximum adsorption capacity and energy of adsorption, respectively. When 1/qe is plotted against 1/Ce, for rhodamine B, fast green, and methylene blue, straight lines (correlation coefficients ranging from 0.9534 to 0.9918) with slopes of 1/bQ0, are obtained, which shows that the adsorption of the three dyes follows the Lang-

1744 Ind. Eng. Chem. Res., Vol. 43, No. 7, 2004 Table 1. Langmuir Constants for the Removal of Rhodamine B, Fast Green, and Methylene Bluea Q0 (mol/g)

b (L/mol)

dye

30 °C

40 °C

50 °C

30 °C

40 °C

50 °C

RL

rhodamine B fast green methylene blue

1.16 × 10-5 9.35 × 10-6 5.23 × 10-5

1.06 × 10-5 8.77 × 10-6 4.81 × 10-5

1.01 × 10-5 7.25 × 10-6 4.35 × 10-5

14.28 × 103 4.88 × 104 1.79 × 102

7.76 × 103 1.66 × 104 1.28 × 102

4.08 × 103 0.61 × 104 0.84 × 102

0.48 0.50 0.89

a Adsorbent dose ) 10 g/L; particle size ) 150-200 mesh; pH 1.0 for rhodamine B, pH 7.0 for fast green, and pH 8.0 for methylene blue.

Table 2. Freundlich Constants for the Removal of Rhodamine B, Fast Green, and Methylene Bluea


30 °C 40 °C 50 °C 0.56 0.57 0.24

0.75 0.73 0.27

-∆G° (kJ/mol) 30 °C 40 °C 50 °C

KF [(mg/g) (L/mg)1/n]

n dye

Table 3. Thermodynamic Parameters for the Removal of Rhodamine B, Fast Green, and Methylene Bluea

0.78 0.75 0.57

30 °C

40 °C

50 °C

1.92 × 10-5 1.62 × 10-5 1.38 × 10-5 1.63 × 10-5 1.19 × 10-5 9.88 × 10-6 4.57 × 10-5 3.55 × 10-5 2.82 × 10-5

Adsorbent dose ) 10 g/L; particle size ) 150-200 mesh; pH 1.0 for rhodamine B, pH 7.0 for fast green, and pH 8.0 for methylene blue. a

muir isotherm. The Langmuir constants b and Q0 were evaluated, and the values of these at the three different temperatures studied, i.e., 30, 40, and 50 °C, are reported in Table 1. For each dye, the Langmuir constants b and Q0 decreased with increasing temperature, indicating the exothermic nature of the adsorption process. The adsorption capacity Q0 appeared to be markedly high for the methylene blue-red mud system and lowest for the fast green-red mud system. The influence of the shape of the isotherm on the feasibility of the process, i.e., whether the sorption is favorable or unfavorable, has been considered by Weber and Chakravorti17 in terms of a dimensionless constant separation factor (RL). The calculated values of the dimensionless factor RL for rhodamine B, fast green, and methylene blue are included in Table 1. The magnitude of the RL values, i.e., (0 < RL < 1) indicates the favorable adsorption of each of the dyes under consideration. Freundlich Isotherm. The adsorption data for rhodamine B, fast green, and methylene blue were also analyzed by Freundlich model. The logarithmic form of Freundlich model is given by

log qe ) log KF + (1/n) log Ce

(2)

where qe is the amount adsorbed (mg/g); Ce is the equilibrium concentration of the adsorbate (mg/L); and KF and n are Freundlich constants related to the adsorption capacity and adsorption intensity, respectively. When log qe is plotted against log Ce for rhodamine B, fast green, and methylene blue, straight lines (correlation coefficients ranging from 0.9135 to 0.9673) with slope 1/n are obtained, which shows that the adsorption of the dyes follows the Freundlich isotherm. However, the Langmuir model fits slightly better with better correlation coefficients compared to Freundlich isotherm, indicating the process to correspond to monolayer adsorption. The Freundlich constants KF and n were evaluated, and their values at the three different temperatures considered, i.e., 30, 40, and 50 °C, are reported in Table 2. From Table 2, it is clear that the values of KF are lowest for the fast green-red mud system and highest for the methylene blue-red mud system. These results indicate that the adsorption capacity of the red mud adsorbent used decreases in the order methylene blue > rhodamine B > fast green.

dye rhodamine B fast green methylene blue

24.1 27.2 13.1

23.3 25.3 12.6

22.3 23.4 11.9

-∆H° (kJ/mol)

-∆S° (J/K‚mol)

67.1 84.6 31.0

140.1 189.6 59.1


Thermodynamic Parameters. Thermodynamic parameters for the adsorption systems were calculated using the following equations

∆G° ) -RT ln b′ ∆H° ) -R ∆S° )

(

)

b2 T2T1 ln T2 - T1 b1

∆H° - ∆G° T

(3) (4)

(5)

where b′, b2, and b1 are the Langmuir constants at 30, 40, and 50 °C, respectively, and were obtained from the Langmuir model. The other terms have their usual meanings. The thermodynamic parameters obtained for the systems under investigation are listed in Table 3. The negative free energy values indicate the feasibility and spontaneous nature of the process, while the negative ∆H° values indicate the exothermic nature of the process. Negative values of the entropy (∆S°) of adsorption reflect the affinity of the adsorbent material for the dyes under investigation and are consistent with the findings reported herein. Kinetic Studies. To determine the applicability of the adsorption processes in wastewater treatment, kinetic studies were also carried out. To evaluate the performance of unit processes utilizing adsorption, it is necessary to have an understanding of the time dependence of the concentration distribution of the organic solute in both the bulk solution and solid adsorbent phases and to identify the rate-determining step. To understand the practical application of adsorption and design a sorption reactor, the kinetic data obtained in this study were treated by the models given by Boyd et al.,18 which are valid under the experimental conditions used. This is in accordance with the observations of Reichenberg.19 The models are given by the following equations

F)1-

6 π

∞

∑ 2 n)1

1

n

2

exp(-n2Bt)

B ) π2Di/r2

(6) (7)

where F is the fractional attainment of equilibrium at

Ind. Eng. Chem. Res., Vol. 43, No. 7, 2004 1745 Table 4. D0, Ea, and ∆S# Values for the Diffusion of Rhodamine B, Fast Green, and Methylene Bluea dye

D0 (m2/s)

-Ea (kJ/mol)

∆S# (J/K‚mol)


2.51 × 10-14 7.48 × 10-13 6.73 × 10-13

31.7 25.3 13.5

157.6 129.4 130.3


Table 5. Values of the Effective Diffusion Coefficients (Di) for Rhodamine B, Fast Green, and Methylene Blue at Different Temperaturesa Di (m2/s) dye

30 °C


40 °C

10-14

7.38 × 15.03 × 10-13 1.07 × 10-12

50 °C

10-14

3.41 × 10-14 8.12 × 10-13 0.77 × 10-12

5.81 × 12.63 × 10-13 0.96 × 10-12


time t and n takes on integral values 1, 2, 3, ... Di is the effective diffusion coefficient of the adsorbate in the adsorbent phase with r being the radius of the adsorbent particle, assumed to be spherical. The fractional attainment of the equilibrium can be determined by the equation

F ) Qt/Q∞

(8)

where Qt and Q∞ are the amounts adsorbed after time t and in the limit of infinite time, respectively. For each calculated value of F, the corresponding values of Bt are calculated from eq 6, and the values of Di are calculated using eq 7. The values of the energy of activation, Ea, were calculated from the following equation

log k2/k1 )

[

]

Ea (T2 - T1) 2.303R T2T1

(9)

where k1 and k2 are the rate constants. The same were also calculated from the slopes (slope ) -Ea/2.303R) of plots of log k versus 1/T (plots not given) (Table 4) and were found in good agreement with those obtained from eq 9. The values of D0, the preexponential constant (analogous to the Arrhenius frequency factor), and ∆S#, the entropy of activation, were calculated from the following equations

[ ] [ ]

Di ) D0 exp D0 ) 2.72d2

Ea RT

kbT ∆S# exp h R

(10) (11)

where d is the average distance between successive exchange sites and is taken as 5 Å. R, h, and kb are the gas, Planck, and Boltzmann constants, respectively. The values of Ea, Di, D0, ∆S#, and other parameters are listed in Tables 4 and 5. The negative values of ∆S# reflect the fact that no significant change occurred in the internal structure of the red mud during the adsorption process. Table 5 contains the values of Di at 30, 40, and

Figure 8. Plots of ln[(Ct/C0) - 1/(1 + mk)] vs time for the mass transfer of rhodamine B, fast green, and methylene blue. Table 6. Mass-Transfer Coefficients (βL) and Rate Constants of Adsorption (Kad) for Rhodamine B, Fast Green, and Methylene Bluea dye

βL (cm/s)

Kad (min-1)

rhodamine B fast green methylene Blue

3.31 × 10-8 4.62 × 10-9 2.09 × 10-9

2.03 × 10-2 4.32 × 10-3 8.98 × 10-3

a Temperature ) 30 °C; adsorbent dose ) 10 g/L; particle size ) 150-200 mesh; pH 1.0 for rhodamine B, pH 7.0 for fast green, and pH 8.0 for methylene blue.

50 °C, and it can be observed from this table that, as the temperature increased, the contribution of the faster component of Di decreases in the cases of rhodamine B and methylene blue. This is because of the decreasing mobility of inward moving species at higher temperature, which, to some extent, overcomes the influence of the retarding forces. In the case of fast green, an increase in the mobility of the ions and a decrease in the retarding forces acting on the diffusing ion result in the enhancement of Di with temperature (Table 5). Mass-Transfer Study. The values of the masstransfer coefficient (βL) for the adsorptions of rhodamine B, fast green, and methylene blue on red mud at 30 °C were calculated from Figure 8 and are reported in Table 6. The linear nature of the plots of ln[(Ct/C0) - 1/(1 + mkL)] versus time [where C0 is the initial concentration of adsorbate (mol/L), Ct is the concentration of adsorbate after time t (mol/L), m is the mass of the adsorbent per unit volume of particle-free adsorbate solution (g/L), and kL is the constant obtained by multiplying Langmuir constants Q0 and b] suggest the validity of the diffusion model for the present systems. The mass-transfer coefficient values suggest that the velocity of adsorbate transport from the bulk to the solid phase is quite rapid, and this reflects the efficacy of red mud for the treatment of dye-bearing wastewater. The values of the rate constants of adsorption (Kad) as calculated from plots (not given) of log(qe - q) versus time at 30 °C are included in Table 6, and these values show the applicability of the first-order rate expression of Lagergren.20 Column Studies. The results obtained from adsorption batch experiments were used to study the removal of rhodamine B, fast green, and methylene blue by

1746 Ind. Eng. Chem. Res., Vol. 43, No. 7, 2004

be further utilized as a raw material for building materials. Therefore, there is no need to regenerate red mud columns. Cost Estimation. The cost of the cheapest variety of carbon available in India is about $285.0 (U.S.) per ton. The waste red mud costs about $25.0 (U.S.) per ton, including the cost of its purchase, transport, and processing (chemicals, electrical energy, and labor required in the process). Therefore, the developed red mud adsorbent can be considered as a good alternative to commercially available carbon. Conclusions

Figure 9. Breakthrough curves of rhodamine B, fast green, and methylene blue.

column. The flow rate was varied to achieve the maximum removal of the adsorbates, and it was found that the maximum uptakes of rhodamine B, fast green, and methylene blue were achieved at a flow rate of 0.5 mL/min. Percentage removals of about 95-97% of rhodamine B, fast green, and methylene blue are achieved at this lower flow rate (0.5 mL/min), but the removal decreases with increasing flow rate. The results obtained from the column experiments for rhodamine b, fast green, and methylene blue were analyzed with the well-known bed-depth-service-time (BDST) model proposed by Hutchins,21 and it was found that the results obtained for each of these dyes obeyed this model very well, thus indicating the feasibility of these column experiments. The measured breakthrough curves (Figure 9) were used to calculate the column capacity at complete exhaustion, and the column capacity was found to be higher than the batch experiments adsorption capacity. The high column capacity might be due to the fact that a large concentration gradient is continuously present at the interface zones as the dyecontaining sample passes through the column whereas the concentration gradient decreases with time in batch experiments. The regeneration and recovery of a column is a very important aspect in wastewater treatment processes, and therefore, desorption of rhodamine B, fast green, and methylene blue was tried with a number of eluents (methanol, ethanol, acetone, sodium hydroxide, sulfuric acid, hydrochloric acid, nitric acid, etc.). It was found that the desorption of these dyes occurred easily with acetone. Therefore, acetone was passed through the column at a flow rate of 2.0 mL/min for about 3 h, followed by doubly distilled water at a flow rate of 2.0 mL/min for the next 3 h. It was observed that the column lost about 1.5% of its capacity after the first run and about 3-10% after more than five runs. Therefore, the column can be used at least for 10 runs without any problem. However, it is very important to mention here that red mud is a readily available and inexpensive material and its cost is very low in comparison to the cost of its regeneration. Moreover, the used red mud can

The removal of rhodamine B, fast green, and methylene blue from wastewater was achieved successfully using red mud, a waste byproduct of the aluminum industry. The adsorption process followed both the Langmuir and Freundlich models and was exothermic in nature. The removals achieved for these dyes were to 71.1-94.0% by the batch method and 95-97% by column operations at a flow rate of 0.5 mL/min. In view of all of these findings, it can be concluded that the developed red mud system can be advantageously applied for the rapid and reproducible removal of rhodamine B, fast green, and methylene blue dyes. Acknowledgment The authors are grateful to the Council of Scientific and Industrial Research (CSIR), New Delhi, India, for financial support. Literature Cited (1) Venkataraman, K. The Chemistry of Synthetic Dyes; Academic Press: New York, 1971; Vol IV. (2) Mattson, J. S.; Mark, H. B. Activated Carbon Surface Chemistry and Adsorption from Aqueous Solution; Marcel Dekker: New York, 1971. (3) Cheremisinoff, P. N.; Ellerbush, F. Carbon Adsorption Handbook; Ann Arbor Science Publishers: Ann Arbor, MI, 1979. (4) Gupta, V. K.; Ali, I. Adsorbents for water treatment: Low cost alternatives to carbon. In Encyclopedia of Surface and Colloid Science; Hubbard, A., Ed.; Marcel Dekker: New York, 2002; Vol. 1, pp 136-166. (5) Pollard, S. J. T.; Fowler, G. D.; Sollars, C. J.; Perry, R. Low cost adsorbents for waste and wastewater treatment: A review. Sci. Total Environ. 1992, 116, 31. (6) Cowan, C. E.; Zachara, J. M.; Resch, C. T. Cadmium adsorption on iron oxides in the presence of alkaline earth elements. Environ. Sci. Technol. 1991, 25, 437. (7) Kesaoul-Qukel, S.; Cheeseman, C.; Perry, R. Effect of conditioning and treatment of chabazite and clinoptilolite prior to lead and cadmium removal. Environ. Sci. Technol. 1993, 27, 1108. (8) Groffman, A.; Peterson, S.; Brookins, D. Removing lead from wastewater using zeolite. Water Environ. Technol. 1992, 5, 54. (9) Lee, C. K.; Low, K. S. Removal of copper from aqueous solution using moss. Environ. Technol. Lett. 1989, 10, 395. (10) Low, K. S.; Lee, C. K. Cadmium uptake by the moss Calyperes delessertii and besch. Bioresour. Technol. 1991, 38, 1. (11) Periasamy, K.; Namasivayam, C. Process development for removal and recovery of cadmium from wastewater by a low cost adsorbent: Adsorption rate and equilibrium studies. Ind. Eng. Chem. Res. 1994, 33, 317. (12) Tan, T. C.; Chia, C. K.; Teo, C. K. Uptake of metal ions by chemically treated human hairs. Water Res. 1985, 19, 157. (13) Rodda, P. D.; Johnson, B. B.; Wello, J. D. The effect of temperature and pH on the adsorption of copper(II), lead(II) and zinc(II) on geolite. J. Colloid Interface Sci. 1993, 161, 57. (14) Fornwalt, H. J.; Hutchins, R. A. Purifying liquids with activated carbon. Chem. Eng. 1966, 73, 179.

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Received for review October 29, 2003 Revised manuscript received January 20, 2004 Accepted January 23, 2004 IE034218G

Removal of Rhodamine B, Fast Green, and ... - ACS Publications

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