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Sorption of acid dyes from aqueous solution by using non-ground ash and slag
Desalination 264 (2010) 78–83
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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 ev i e r. c o m / l o c a t e / d e s a l
Sorption of acid dyes from aqueous solution by using non-ground ash and slag Ayten Genc ⁎, Askin Oguz Department of Environmental Engineering, Zonguldak Karaelmas University, 67100 Zonguldak, Turkey
a r t i c l e
i n f o
Article history: Received 10 February 2010 Received in revised form 2 July 2010 Accepted 2 July 2010 Available online 31 July 2010 Keywords: Sorption Acid dyes Furnace Bottom Ash Granulated Blast Furnace Slag
a b s t r a c t The sorption of two acid dyes (Acid Yellow 99 and Acid Red 183) into locally available industrial waste materials, namely, Granulated Blast Furnace Slag (GBFS) and Furnace Bottom Ash (FBA), has been investigated by performing batch equilibrium experiments with pH, ionic conductivity, initial dye concentration and temperature as variables. The kinetic sorption data indicated that the sorption capacity of GBFS for these dyes was almost zero. On the other hand, the color removal efficiency for FBA could reach 50% depending on the initial dye concentration. It was also found that the kinetics of sorption of Acid Yellow 99 and Acid Red 183 onto the surface of FBA at different operating conditions were best described by the Elovich kinetic model. In addition, the adsorption equilibrium data were analyzed using various adsorption isotherm models and the results have shown that the sorption behaviors of the studied dyes could be best described by the Langmuir model. © 2010 Elsevier B.V. All rights reserved.
1. Introduction Dyes are coloring materials and are one of the major constituents of the wastewater discharged from many industries including textile, leather, cosmetics, paper, printing, plastic, food and pharmaceuticals. They are visible even at concentrations as low as 0.005 ppm and can therefore create aesthetic problems. However, more important than any potential aesthetic problem is that the dyes can cause health problems, may affect growth of microorganisms and can hinder photosynthesis in aquatic plants [1]. Moreover, the complex aromatic molecular structures of dyes make them more stable and more difficult to biodegrade in water. Various methods for dye removal from wastewaters exist including adsorption, coagulation, ultrafiltration, chemical oxidation and photocatalytic oxidation [2]. Amongst these methods, adsorption techniques employing activated carbon have been found to be reasonably effective in the removal of dyes [3]. However, activated carbon is quite expensive, and its use results in considerable loss (10– 15%) of the adsorbent during regeneration [4]. Economic considerations require the use of inexpensive and locally available materials as the adsorbent for the removal of dyes. Such adsorbents range from industrial waste products [5–7] such as waste rubber tires, blast furnace slag, bottom ash and lignin, to agricultural products [8,9] such as wool, rice straw, coconut husk, sawdust, and peat moss. In addition, the low cost and commercial availability of biosorbents have increased attention in their use in recent years [10].
⁎ Corresponding author. Tel.: + 90 372 2574010; fax: + 90 372 2574023. E-mail address: [email protected] (A. Genc). 0011-9164/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.desal.2010.07.007
The prime objective of the present study is to explore the use of Granulated Blast Furnace Slag (GBFS) and Furnace Bottom Ash (FBA), which are locally available, as a sorbent in color removal from wastewater and to investigate the kinetics and mechanisms involved in dye adsorptions on GBFS and FBA. GBFS is a by-product obtained in the production of pig iron in blast furnaces and is formed by the combination of earthy constituents of iron ore with limestone flux. When the molten slag is swiftly quenched with water, it forms a fine, granular, almost fully noncrystalline and glassy form, which is known as granulated slag. Due to the presence of high contents of silica and alumina in a non-crystalline state, GBFS is used as a cementitious ingredients in mortars, as an additive in blending cements, as fine aggregates or as mineral admixtures in concrete [11]. FBA, on the other hand, is a by-product of coal-fired power plants, where it agglomerates and settles down to the bottom of the combustion furnace. Its applications include structural fills, road bases and sub-bases, asphalt fillers, roofing granules, sandblasting grit and aggregates in cement and concrete products. 2. Materials and methods 2.1. Physical and chemical properties of sorbents GBFS was obtained from the Erdemir Iron and Steel Production Plant, which is located in the eastern Black Sea region of Turkey (Zonguldak). Çatalağzı thermal power plant, where bituminous coal is the main fuel, is also located in the same region and FBA was obtained from this plant. The physical properties of GBFS and FBA are reported in Table 1. Atomic absorption spectrophotometry techniques were used for the chemical analyses of GBFS and FBA and the results has
A. Genc, A. Oguz / Desalination 264 (2010) 78–83 Table 1 Physical properties of GBFS and FBA. Property
GBFS
FBA
Loose unit weight, kg/m3 Compact unit weight, kg/m3 Specific gravity, g/cm3 Absorption (%) Amount of clay (%) Loss on ignition (%) Prop. of lightweight particles (%)
1052 1236 2.08 8.30 1 1.8 3.00
620 660 1.39 6.10 2.0 2.4 7.00
been presented in Table 2. Major components in both sorbents were SiO2, Al2O3, CaO and MgO. In this study, it was aimed to investigate GBFS and FBA as sorbents in their original form, i.e., as they were taken from the plants and were not grinded. As a result, the cost of sorbents was kept at minimum. Because of not grinding, the smallest mesh opening has been selected and the GBFS/FBA samples were sieved by 250 μm opening. Then they were dried at 105 °C for 24 h and no extra treatment was applied to either sorbents. 2.2. Sorbates Commercial quality acid dyes (Acid Red 183, C.I. 18,800, C16H11ClN4Na2O8S2.xCr, MW: 584.86 g/gmol and Acid Yellow 99, C.I. 13,900, C16H13N4NaO8S.Cr, MW: 496.4 g/gmol) were obtained from Aldrich and used without any further purification. These dyes are watersoluble dyes, which are widely used in wool and leather dying. The chemical structures of Acid Red 183 and Acid Yelow 99 are presented in Fig. 1. Both dyes are characterized by the presence of a hydroxyl group ortho to the azo-group and are colored aromatic compounds which require the presence of chromium. However, it is known that incomplete reduction of dichromate could lead to release of the toxic chromium (VI) salt into the environment [12]. Therefore, wastewater containing these dyes has to be treated before discharge. 2.3. Batch equilibrium experiments Adsorption studies were performed by batch equilibrium experiments. Aqueous solutions were prepared by dissolving dyes in distilled water at the concentration of 20, 40, 60, 80, 100 and 120 mg L− 1. Solutions were prepared by using distilled water to minimize interferences in the study. The studied pH range was 4 to 8. The solution pH was set to desired value by using HCl before the addition of sorbents. After the adjustment of pH, 400 mL of the dye solution was replaced in a glass flask and 4 g sorbents was introduced. Sorbent to liquid ratios were kept constant at 10 g/L during the all adsorption experiments. Then, the glass flasks were submerged into a temperature controlled water bath and the temperature was set to 20 °C. The glass flasks were shaken for a day and the sorbents were separated from the dye solutions by centrifuging at 3600 rpm and filtered (whatman 42) at the end of mixing. The residual dye color in the solution was analyzed colorimetrically using a spectrophotometer (UV–VIS Spectrophotometer Pharo 300 Spectroquant). To evaluate dye removal, color concentrations were measured before and after the experiment by measuring absorbance. The maximum wavelengths for
Table 2 Chemical compositions of GBFS and FBA (%). SiO2
CaO
MgO Al2O3 Na2O S
GBFS 35.09 37.79 5.50 FBA 57.90 2.00 3.20
K2O
MnO Fe2O3 TiO2 P2O3
17.54 0.30 0.66 – 0.83 22.60 0.086 – 0.604 –
– 6.50
0.68 0.37 – –
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Acid Red 183 and Acid Yellow 99 was determined experimentally and found as 483 nm and 464 nm, respectively. The amount of dye adsorbed by GBFS or FBA was calculated by: qe =
ðC 0 C e ÞV W
ð1Þ
where qe, Co, Ce, V and W represent the amount of dye removed from solution per unit mass of sorbent (mg g− 1) at equilibrium, the concentration of dye in the solution before mixing with sorbent (mg L− 1), the equilibrium concentration of dye left in the solution (mg L− 1), the solution volume (L) and the weight of dried GBFS or FBA (g), respectively. 2.4. Sorption dynamics The adsorption mechanisms of Acid Red 183 and Acid Yelow 99 on GBFS or FBA was analyzed by using pseudo first order, pseudo second order, Elovich and Weber–Morris intraparticle rate equations. According to pseudo first order equation model, dye adsorption on GBFS or FBA can be considered as a reversible process and equilibrium has been attained between the liquid and solid phases. It assumes that the rate of change of dye adsorption with time is a linear function of the difference between the dye uptakes at equilibrium and time t and adsorption can be described as the diffusion control process. It is generally written as [13]: dq = k1 ðqe −qÞ dt
ð2Þ
where q is the amount of lead adsorbed per unit mass of adsorbent (dye uptake) at time t, and k1 is the pseudo first order rate constant. While the pseudo first order kinetic model is used for interparticle and intraparticle mass transfer mechanisms, the reaction kinetics approximation is usually employed for systems where the reaction step at pore surfaces is the controlling step. In this case, the adsorption dynamics can be represented by a second order reaction rate constant as [14]: dq 2 = k2 ðqe −qÞ dt
ð3Þ
where k2 is the pseudo second order rate constant. Elovich's equation is another kinetic model, which is based on the adsorption capacity and can be derived from either a diffusioncontrolled process or a reaction-controlled process [15]: dq −bq = ae dt
ð4Þ
where ‘a’ and ‘b’ are constants and represent the initial adsorption rate and the surface coverage, respectively. Finally, the intraparticle diffusion model of Weber and Morris [16] has been tested. According to this model, the variation of dye uptake with time can be represented as: pffiffi q = ki t
ð5Þ
where ki is the intraparticle diffusion constant. Eq. (5) yields a parabola with the initial curved portion showing a surface adherence or boundary layer effect; and the following linear part identifies intraparticle or pore diffusion and the slope gives ki. If the intercept is zero the surface adherence in the sorption rate-limiting step is negligible. The larger the intercept the greater is the contribution to the surface adherence in the rate-limiting step.
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Fig. 1. Chemical structures of dyes.
2.5. Equilibrium isotherms Four two-parameter adsorption isotherms (Langmuir, Freundlich, Temkin and Dubinin–Radushkevich) have been studied for the adsorption of Acid Red 183 and Acid Yellow 99 on GBFS/FBA. In addition, effects of operating parameters, such as, initial dye concentration, solution pH, ionic conductivity and temperature on sorption were investigated. 3. Results and discussions 3.1. Sorption capacities of GBFS and FBA Almost no color removal was observed in the batch equilibrium experiments when GBFS was used as a sorbent, even when the concentration of dye was increased to 100 mg/L. It was clear that GBFS didn't adsorb Acid Yellow 99 and Acid Red 183. Sorption studies of dyes on GBFS and FBA are limited in the literature and some are listed in Table 3. When the sorbent is only sieved and dried, then the phrase ‘no treatment’ is used in the table. Ramakrishna and Viraraghavan [17] studied GBFS in the sorption of different classes of dyes and postulated that GBFS was effective for disperse dye removals at low pH values and less effective in acid dye removals. Even though, Jain et al. [6] applied some heat treatments on GBFS, they concluded that GBFS was not suitable for the sorption of dyes. On the other hand, Kostura et al. [18] and Nehrenheim and Gustafsson [19] showed that GBFS could successfully be used as a sorbent in the removal of phosphorous and heavy metals from waste waters. As it can be seen in Table 2, GBFS is a complex CaO–Al2O3–SiO2–MgO system and has a number of minor components of other metals oxides. The oxides have a tendency to form metalhydroxide complexes in solution and the reactions of these oxides with water may be alkaline (CaO), acidic (SiO2) or amphoteric (MgO, Al2O3) [24]. Therefore, the Table 3 Use of Granulated Blast Furnace Slag (GBFS) and Furnace Bottom Ash (FBA) as a sorbent. Sorbent Sorbate
Treatment
Reference
GBFS
Basic Red Anionic dyes Cationic dyes Anionic and disperse dyes Phosphorus Heavy metals
Activated at 600 °C Activated at 400 °C Activated at 400 °C No treatment
Acidic dye
With hydrogen peroxide With hydrogen peroxide No treatment No treatment
Gupta et al. [5] Jain et al. [6] Bhatnagar and Jain [7] Ramakrishna and Viraraghavan [17] Kostura et al. [18] Nehrenheim and Gustafsson [19] Gupta et al. [20]
FBA
Indigo dye Reactive dyes Phosphorus
No treatment No treatment
Mittal et al. [21] Dincer et al. [22] Yan et al. [23]
dissociations of these complexes at the solid-solution interface leads to development of a positive or negative charge on the surface. In the case of net negative surface charge on GBFS, both dyes might be repelled because Acid Yellow 99 and Acid Red 183 are first dissolved in water and the sulfonate groups of dyes are converted to anionic dye ions (Fig. 1). Acid Yellow 99 and Acid Red 189 were sorbed by FBA and removal efficiencies from water were in the range of 30%–50% depending on initial dye concentrations even though no treatment was applied to FBA, i.e., it was only sieved and dried. The sorption dynamics and equilibrium isotherms of both dyes on FBA will be discussed in more detail in the following sections. Moreover, effects of operating parameters, such as, initial dye concentration, solution pH, ionic conductivity and temperature will be investigated. 3.2. Sorption mechanisms of dyes on FBA The pseudo first order, pseudo second order, Elovich and Weber– Morris rate equations were tested for the sorption of Acid Yellow 99 and Acid Red 183 by FBA. The related constants for each kinetic model were evaluated from the linear forms and are presented in Table 4. The evaluated correlation coefficients are presented in the table as well. It can be seen that the numerical values for the correlation coefficients are within acceptable limits and that they are higher than 0.85 for the pseudo first and the pseudo second order kinetics. The lowest value (0.51) was obtained for the Elovich rate equation. By looking at only the correlation coefficients, it could be said that the sorption mechanism of dyes onto FBA could be explained best by the pseudo second order kinetics. However, when the calculated qe values from models were compared with the experimental qe values (first row of Table 4), it could be concluded that both pseudo first and pseudo second order kinetics could explain the sorption mechanism of dyes on FBA quite effectively. In order to analyze sorption mechanisms, variations in dye uptakes (q) with time were determined experimentally. 1 L of dye solutions was prepared at the desired concentration in a glass flask and 10 g of FBA was added. The pH of dye solution was around 8 and no NaCl was added. Then the dye solutions was shaken and 10 mL samples were taken at 5, 15, 30, 45, 60, 90, 120, 150, 180, 240, 360, 480, 550, 1400, 1500, 1600 and 1800 min of adsorption. The residual dye concentrations in the samples were measured by spectrophotometer and the results were shown in Fig. 2. It can be seen that the sorption of both dyes is a very fast process and most of dye sorption on FBA was almost attained in the first 100 min. The q values can also be predicted from the studied kinetic models based on the numerical values presented in Table 4. For the sorption of Acid Yellow 99, the predictions of q values from the pseudo first order, pseudo second order and Elovich rate equations were presented in Fig. 3. The results have presented separately for 10 mg/L, 50 mg/L and 100 mg/L initial dye concentrations. The experimental q values were shown in the graphs as well which were evaluated from Eq. (1) using the numerical values presented in Fig. 2. Among the studied kinetic models, there is no doubt that the Elovich rate equation explains best the sorption of Acid Yellow 99 sorption onto FBA since the predicted q
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Table 4 Sorption kinetics constants. Co (mg/L)
Acid Yellow 99 10
Experimental qe (mg/g) Pseudo first order k1 (1/min) qe (mg/g) R2 Pseudo second order k2 (1/min) qe (mg/g) h (mg/g min) R2 Elovich equation a (mg/g min) b (g/mg) R2
0.8 3.3 × 10 0.60 0.99
Acid Red 183 50
100
2.1 −3
1.3 × 10 1.37 0.87
20
3.2 −3
50
0.5
1.0 × 10 2.64 0.85
−3
5.1 × 10 0.43 0.90
100
1.0 −3
1.7 × 10 1.06 0.92
0.6 −3
4.4 × 10− 3 0.40 0.89
0.03 0.66 0.01 0.97
0.04 1.17 0.06 0.99
0.01 1.40 0.03 0.91
0.01 0.54 4.30 × 10− 3 0.94
3.95 × 10− 3 0.83 2.72 × 10− 3 0.99
0.05 0.55 0.01 0.98
0.06 10.05 0.83
0.92 6.95 0.98
0.57 6.53 0.51
0.01 10.87 0.91
0.01 9.70 0.74
0.06 13.72 0.78
values are very close to experimental values. The predictions of q were overestimated by the pseudo second order kinetics model and the overestimation increases with an increase in the initial dye concentration. On the other hand, the predictions of q by the pseudo first order kinetics model were lower than the experimental values but the discrepancies were decreasing by the initial dye concentration. Similar observations were obtained for the sorption of Acid Red 183. Depending on the results obtained from Fig. 3, it could be concluded that the best kinetic model could not be decided only by looking at numerical values of the correlation coefficients. If the kinetic models are evaluated from their linear forms, it is best to check the evaluated model constants by using integral forms of the kinetic models. Especially for the pseudo first and pseudo second order kinetics, the qe values obtained from the intercept should be equal to the one obtained from the experiment. Dye molecules are large organic molecules and, therefore, the diffusion-controlled mechanisms can be important. Therefore, Weber–Morris intraparticle diffusion model has been tested. According to this model, the variations in Acid Yellow 99 uptakes on FBA were drawn with respect to the square root of time for 10 mg/L and 50 mg/L initial dye concentrations and the results are shown in Fig. 4. When the initial dye concentration was 10 mg/L, it was clear that the rate-controlling step was only the intraparticle diffusion and the surface adherence in the sorption ratelimiting step is negligible. The intraparticle rate constant (ki) was evaluated from the slope and was found to be 0.03 mg/g min0.5. On the other hand, as the concentration of dye increased to 50 mg/ L, the effects of surface hindrance on sorption rate increased since
the intercept changed from 0 to 0.6 even though ki stayed constant at 0.03 mg/g min0.5. 3.3. Adsorption isotherms The equations and evaluated constants for the Langmuir, Freundlich, Temkin and Dubinin–Radushkevich adsorption isotherms are presented in Table 5. All of the isotherms have different assumptions. Langmuir adsorption isotherm assumes that the adsorption sites are identical; each site retains one molecule of adsorbate, and all sites are energetically independent of the adsorbed quantity. On the other hand, the Freundlich adsorption isotherm assumes a heterogeneous surface with a non-uniform distribution of heat of adsorption. The Dubinin–Radushkevich isotherm explains the adsorption mechanism based on potential theory assuming heterogeneous surfaces as well. Temkin isotherm, however, assumes that binding energies of molecules are distributed uniformly and the heat of adsorption decreases linearly. For both dyes, it was not possible to represent the relation between dye uptakes and concentrations at equilibrium by using the Freundlich isotherm because negative KF values were obtained. However, it is not physically meaningful since adsorption capacity cannot be negative. For the sorption of Acid Red 183, only the Langmuir isotherm was within acceptable regression limits, i.e., correlation coefficient better than 0.8. In the case of the sorption of Acid Yellow 99, the Langmuir, Temkin and Dubinin–Radushkevich isotherms were calculated even though the correlation coefficient was very low for the Temkin
Fig. 2. Dye uptakes of FBA for different initial dye concentrations (pH: 8).
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A. Genc, A. Oguz / Desalination 264 (2010) 78–83 Table 5 Comparison of equilibrium isotherms. Equation
Isotherm constants
Acid Yellow 99
Acid Red 183
Langmuir
L aL C e qe = 1K+ aL C e
Freundlich
qe = KF Ce
Temkin
qe = bRT InðKTe Ce Þ
qe = qm Exp
2.45 0.14 0.94 Not possible 8.49 0.93 0.53 0.33 2.42 0.90
0.80 0.18 0.80 Not possible Not possible
Dubinin– Radushkevich
KL (mg/g) aL (L/mg) R2 KF n b (J/g) KTe (L/mg) R2 E (J/g) qm (mg/g) R2
1=n
Te
"
RT In 1 + −2E 2
1 Ce
2 #
Not possible
3.4. Effects of operating conditions
Fig. 3. Comparison of kinetic models predictions for the sorption of Acid Yellow 99 on FBA ((a) Co = 10 mg/L, (b) Co = 50 mg/L, (c) Co = 100 mg/L).
isotherm (0.53). When the numerical values of the Langmuir and Dubinin–Radushkevich isotherms constants (KL and qm) were compared, their predictions for the adsorption capacity of FBA were almost in the same order of magnitude. In addition, the magnitude of the second constant in the Dubinin–Radushkevich isotherm (E) was very small, which indicated that the adsorption energy is very low. This also suggests that the sorption of dyes onto FBA is a physical process and not a chemical reaction.
Fig. 4. Weber–Morris plots for the intraparticle transport of Acid Yellow 99.
Effects of initial dye concentrations on the sorption kinetics of Acid Yellow 99 and Acid Red 183 dyes onto FBA were studied by performing kinetic experiments at 10 mg/L, 50 mg/L and 100 mg/L dye concentrations and the results are presented in Fig. 3. For both dyes, the dye removal efficiencies decreased as the initial dye concentration increased. In addition, the removal efficiencies were very low when the initial dye concentration was 100 mg/L, where the maximum sorption capacity of FBA could be reached. In the comparison of both dyes, it was observed that the removal efficiencies for Acid Yellow 99 were always higher than the ones obtained for Acid Red 183. The dye removal efficiencies for Acid Yellow 99 were 53%, 44% and 15% for the three initial dye concentrations studied. On the other hand, the corresponding values for Acid Red 183 were 27%, 16% and 5%, respectively. When the structural formulas of both dyes are compared (Fig. 1) it can be observed that Acid Red 183 is a bigger molecule than Acid Yellow 99. Therefore, it could be much easier for Acid Yellow 99 to enter the pores of FBA. When both dyes were present in the solution, this effect was much clearer. For a constant total dye concentration, the dye removal efficiency of FBA increased more if the percentage of Acid Yellow 99 in the binary mixture of dyes increased. However, no such dependency was observed for Acid Red 183. It is very well known that pH is one of the important parameters in sorption studies [25] and, therefore, the sorption experiments for Acid Yellow 99 and Acid Red 183 dyes were repeated at different pH values by varying the initial dye concentrations. When the dyes were mixed with water, the solution pH was around 8–8.6. The batch equilibrium experiments were repeated under pH values of 4, 6 and 8 by adjusting pH with hydrochloric acid. The results showed that the increase of pH from 4 to 6 or 8 does not cause appreciable changes in dye uptakes by FBA. For example, when the initial dye concentration and pH were 60 mg/L and 4, the dye removal efficiencies for Acid Yellow 99 and Acid Red 183 were 44% and 17.3%, respectively. When the pH was increased to 8, the dye removal efficiency values changed to 49% and 15%, respectively. Similar results were observed for the other studied initial dye concentrations. The effects of ionic conductivity were investigated by adding NaCl (5 mg/L, 10 mg/L and 50 mg/L). It was observed that the addition of NaCl didn't cause any improvement in the sorption rate of both dyes; rather it caused slight decreases in the dye removal efficiencies. Increasing ionic conductivity could increase competition between ions for the sorption sites and therefore, the dye removals for both dyes could be reduced because they were ionic dyes in structure. The sorption experiments were performed at 20 °C and 40 °C and no appreciable change in the adsorbed quantity of dyes were observed over this temperature range. These results also suggest that the sorption of Acid Yellow 99 and Acid Red 183 are likely to
A. Genc, A. Oguz / Desalination 264 (2010) 78–83
be a physical diffusion process rather than a chemical reaction. This type of adsorption is likely classified as reversible and temperature dependence on adsorption would be comparatively weaker than desorption [26]. 4. Conclusions FBA and GBFS have been tested experimentally in the removal of two acid dyes (Acid Red 183 and Acid Yellow 99) from aqueous solutions. In the preparation of FBA and GBFS, they were only sieved by 250 μm opening mesh and no grinding was applied. Based on the experimental investigation and evaluated sorption kinetics, the following conclusions are drawn: - GBFS cannot be used as a sorbent for the removal of Acid Yellow 99 and Acid Red 183 from wastewater. - FBA can be used as an efficient sorbent for the removal of Acid Yellow 99 and Acid Red 183 from wastewater. Dye removal efficiencies can reach up to 50%. - The use FBA as a sorbent can be economical since no grinding is applied. - The sorption mechanisms of dyes on FBA are likely to be a physical diffusion process rather than a chemical reaction. - The rate-limiting step is found to be the intraparticle diffusion at lower dye concentration. As the dye concentration increases, the effect of surface hindrance on sorption rate is observed to increase. - The sorption mechanisms of Acid Yellow 99 and Acid Red 183 on FBA are found to be best described by the Elovich kinetic model. - The Langmuir isotherm gives the best fit for the sorption of Acid Yellow 99 and Acid Red 183 on FBA. - The dye removal efficiencies are not changed when pH is increased from 4 to 8. - Increasing temperature from 20 °C to 40 °C does not cause any improvements in the sorption of both dyes on FBA. - No effects of NaCl addition has been observed for the sorption of dyes on FBA. References [1] V.K. Gupta, Suhas, Application of low-cost adsorbents for dye removal — a review, J. Environ. Manage. 90 (2009) 2313–2342. [2] F. Fu, Y. Xiong, B. Xie, R. Chen, Adsorption of Acid Red 73 on copper dithiocarbamate precipitate-type solid wastes, Chemosphere 66 (2007) 1–7. [3] R.S. Juang, F.C. Wu, R.L. Tseng, The ability of activated clay for the adsorption of dyes from aqueous solutions, Environ. Technol. 18 (1997) 525–531.
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Sorption of acid dyes from aqueous solution by using non-ground ash and slag Ayten Genc ⁎, Askin Oguz Department of Environmental Engineering, Zonguldak Karaelmas University, 67100 Zonguldak, Turkey
a r t i c l e
i n f o
Article history: Received 10 February 2010 Received in revised form 2 July 2010 Accepted 2 July 2010 Available online 31 July 2010 Keywords: Sorption Acid dyes Furnace Bottom Ash Granulated Blast Furnace Slag
a b s t r a c t The sorption of two acid dyes (Acid Yellow 99 and Acid Red 183) into locally available industrial waste materials, namely, Granulated Blast Furnace Slag (GBFS) and Furnace Bottom Ash (FBA), has been investigated by performing batch equilibrium experiments with pH, ionic conductivity, initial dye concentration and temperature as variables. The kinetic sorption data indicated that the sorption capacity of GBFS for these dyes was almost zero. On the other hand, the color removal efficiency for FBA could reach 50% depending on the initial dye concentration. It was also found that the kinetics of sorption of Acid Yellow 99 and Acid Red 183 onto the surface of FBA at different operating conditions were best described by the Elovich kinetic model. In addition, the adsorption equilibrium data were analyzed using various adsorption isotherm models and the results have shown that the sorption behaviors of the studied dyes could be best described by the Langmuir model. © 2010 Elsevier B.V. All rights reserved.
1. Introduction Dyes are coloring materials and are one of the major constituents of the wastewater discharged from many industries including textile, leather, cosmetics, paper, printing, plastic, food and pharmaceuticals. They are visible even at concentrations as low as 0.005 ppm and can therefore create aesthetic problems. However, more important than any potential aesthetic problem is that the dyes can cause health problems, may affect growth of microorganisms and can hinder photosynthesis in aquatic plants [1]. Moreover, the complex aromatic molecular structures of dyes make them more stable and more difficult to biodegrade in water. Various methods for dye removal from wastewaters exist including adsorption, coagulation, ultrafiltration, chemical oxidation and photocatalytic oxidation [2]. Amongst these methods, adsorption techniques employing activated carbon have been found to be reasonably effective in the removal of dyes [3]. However, activated carbon is quite expensive, and its use results in considerable loss (10– 15%) of the adsorbent during regeneration [4]. Economic considerations require the use of inexpensive and locally available materials as the adsorbent for the removal of dyes. Such adsorbents range from industrial waste products [5–7] such as waste rubber tires, blast furnace slag, bottom ash and lignin, to agricultural products [8,9] such as wool, rice straw, coconut husk, sawdust, and peat moss. In addition, the low cost and commercial availability of biosorbents have increased attention in their use in recent years [10].
⁎ Corresponding author. Tel.: + 90 372 2574010; fax: + 90 372 2574023. E-mail address: [email protected] (A. Genc). 0011-9164/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.desal.2010.07.007
The prime objective of the present study is to explore the use of Granulated Blast Furnace Slag (GBFS) and Furnace Bottom Ash (FBA), which are locally available, as a sorbent in color removal from wastewater and to investigate the kinetics and mechanisms involved in dye adsorptions on GBFS and FBA. GBFS is a by-product obtained in the production of pig iron in blast furnaces and is formed by the combination of earthy constituents of iron ore with limestone flux. When the molten slag is swiftly quenched with water, it forms a fine, granular, almost fully noncrystalline and glassy form, which is known as granulated slag. Due to the presence of high contents of silica and alumina in a non-crystalline state, GBFS is used as a cementitious ingredients in mortars, as an additive in blending cements, as fine aggregates or as mineral admixtures in concrete [11]. FBA, on the other hand, is a by-product of coal-fired power plants, where it agglomerates and settles down to the bottom of the combustion furnace. Its applications include structural fills, road bases and sub-bases, asphalt fillers, roofing granules, sandblasting grit and aggregates in cement and concrete products. 2. Materials and methods 2.1. Physical and chemical properties of sorbents GBFS was obtained from the Erdemir Iron and Steel Production Plant, which is located in the eastern Black Sea region of Turkey (Zonguldak). Çatalağzı thermal power plant, where bituminous coal is the main fuel, is also located in the same region and FBA was obtained from this plant. The physical properties of GBFS and FBA are reported in Table 1. Atomic absorption spectrophotometry techniques were used for the chemical analyses of GBFS and FBA and the results has
A. Genc, A. Oguz / Desalination 264 (2010) 78–83 Table 1 Physical properties of GBFS and FBA. Property
GBFS
FBA
Loose unit weight, kg/m3 Compact unit weight, kg/m3 Specific gravity, g/cm3 Absorption (%) Amount of clay (%) Loss on ignition (%) Prop. of lightweight particles (%)
1052 1236 2.08 8.30 1 1.8 3.00
620 660 1.39 6.10 2.0 2.4 7.00
been presented in Table 2. Major components in both sorbents were SiO2, Al2O3, CaO and MgO. In this study, it was aimed to investigate GBFS and FBA as sorbents in their original form, i.e., as they were taken from the plants and were not grinded. As a result, the cost of sorbents was kept at minimum. Because of not grinding, the smallest mesh opening has been selected and the GBFS/FBA samples were sieved by 250 μm opening. Then they were dried at 105 °C for 24 h and no extra treatment was applied to either sorbents. 2.2. Sorbates Commercial quality acid dyes (Acid Red 183, C.I. 18,800, C16H11ClN4Na2O8S2.xCr, MW: 584.86 g/gmol and Acid Yellow 99, C.I. 13,900, C16H13N4NaO8S.Cr, MW: 496.4 g/gmol) were obtained from Aldrich and used without any further purification. These dyes are watersoluble dyes, which are widely used in wool and leather dying. The chemical structures of Acid Red 183 and Acid Yelow 99 are presented in Fig. 1. Both dyes are characterized by the presence of a hydroxyl group ortho to the azo-group and are colored aromatic compounds which require the presence of chromium. However, it is known that incomplete reduction of dichromate could lead to release of the toxic chromium (VI) salt into the environment [12]. Therefore, wastewater containing these dyes has to be treated before discharge. 2.3. Batch equilibrium experiments Adsorption studies were performed by batch equilibrium experiments. Aqueous solutions were prepared by dissolving dyes in distilled water at the concentration of 20, 40, 60, 80, 100 and 120 mg L− 1. Solutions were prepared by using distilled water to minimize interferences in the study. The studied pH range was 4 to 8. The solution pH was set to desired value by using HCl before the addition of sorbents. After the adjustment of pH, 400 mL of the dye solution was replaced in a glass flask and 4 g sorbents was introduced. Sorbent to liquid ratios were kept constant at 10 g/L during the all adsorption experiments. Then, the glass flasks were submerged into a temperature controlled water bath and the temperature was set to 20 °C. The glass flasks were shaken for a day and the sorbents were separated from the dye solutions by centrifuging at 3600 rpm and filtered (whatman 42) at the end of mixing. The residual dye color in the solution was analyzed colorimetrically using a spectrophotometer (UV–VIS Spectrophotometer Pharo 300 Spectroquant). To evaluate dye removal, color concentrations were measured before and after the experiment by measuring absorbance. The maximum wavelengths for
Table 2 Chemical compositions of GBFS and FBA (%). SiO2
CaO
MgO Al2O3 Na2O S
GBFS 35.09 37.79 5.50 FBA 57.90 2.00 3.20
K2O
MnO Fe2O3 TiO2 P2O3
17.54 0.30 0.66 – 0.83 22.60 0.086 – 0.604 –
– 6.50
0.68 0.37 – –
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Acid Red 183 and Acid Yellow 99 was determined experimentally and found as 483 nm and 464 nm, respectively. The amount of dye adsorbed by GBFS or FBA was calculated by: qe =
ðC 0 C e ÞV W
ð1Þ
where qe, Co, Ce, V and W represent the amount of dye removed from solution per unit mass of sorbent (mg g− 1) at equilibrium, the concentration of dye in the solution before mixing with sorbent (mg L− 1), the equilibrium concentration of dye left in the solution (mg L− 1), the solution volume (L) and the weight of dried GBFS or FBA (g), respectively. 2.4. Sorption dynamics The adsorption mechanisms of Acid Red 183 and Acid Yelow 99 on GBFS or FBA was analyzed by using pseudo first order, pseudo second order, Elovich and Weber–Morris intraparticle rate equations. According to pseudo first order equation model, dye adsorption on GBFS or FBA can be considered as a reversible process and equilibrium has been attained between the liquid and solid phases. It assumes that the rate of change of dye adsorption with time is a linear function of the difference between the dye uptakes at equilibrium and time t and adsorption can be described as the diffusion control process. It is generally written as [13]: dq = k1 ðqe −qÞ dt
ð2Þ
where q is the amount of lead adsorbed per unit mass of adsorbent (dye uptake) at time t, and k1 is the pseudo first order rate constant. While the pseudo first order kinetic model is used for interparticle and intraparticle mass transfer mechanisms, the reaction kinetics approximation is usually employed for systems where the reaction step at pore surfaces is the controlling step. In this case, the adsorption dynamics can be represented by a second order reaction rate constant as [14]: dq 2 = k2 ðqe −qÞ dt
ð3Þ
where k2 is the pseudo second order rate constant. Elovich's equation is another kinetic model, which is based on the adsorption capacity and can be derived from either a diffusioncontrolled process or a reaction-controlled process [15]: dq −bq = ae dt
ð4Þ
where ‘a’ and ‘b’ are constants and represent the initial adsorption rate and the surface coverage, respectively. Finally, the intraparticle diffusion model of Weber and Morris [16] has been tested. According to this model, the variation of dye uptake with time can be represented as: pffiffi q = ki t
ð5Þ
where ki is the intraparticle diffusion constant. Eq. (5) yields a parabola with the initial curved portion showing a surface adherence or boundary layer effect; and the following linear part identifies intraparticle or pore diffusion and the slope gives ki. If the intercept is zero the surface adherence in the sorption rate-limiting step is negligible. The larger the intercept the greater is the contribution to the surface adherence in the rate-limiting step.
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Fig. 1. Chemical structures of dyes.
2.5. Equilibrium isotherms Four two-parameter adsorption isotherms (Langmuir, Freundlich, Temkin and Dubinin–Radushkevich) have been studied for the adsorption of Acid Red 183 and Acid Yellow 99 on GBFS/FBA. In addition, effects of operating parameters, such as, initial dye concentration, solution pH, ionic conductivity and temperature on sorption were investigated. 3. Results and discussions 3.1. Sorption capacities of GBFS and FBA Almost no color removal was observed in the batch equilibrium experiments when GBFS was used as a sorbent, even when the concentration of dye was increased to 100 mg/L. It was clear that GBFS didn't adsorb Acid Yellow 99 and Acid Red 183. Sorption studies of dyes on GBFS and FBA are limited in the literature and some are listed in Table 3. When the sorbent is only sieved and dried, then the phrase ‘no treatment’ is used in the table. Ramakrishna and Viraraghavan [17] studied GBFS in the sorption of different classes of dyes and postulated that GBFS was effective for disperse dye removals at low pH values and less effective in acid dye removals. Even though, Jain et al. [6] applied some heat treatments on GBFS, they concluded that GBFS was not suitable for the sorption of dyes. On the other hand, Kostura et al. [18] and Nehrenheim and Gustafsson [19] showed that GBFS could successfully be used as a sorbent in the removal of phosphorous and heavy metals from waste waters. As it can be seen in Table 2, GBFS is a complex CaO–Al2O3–SiO2–MgO system and has a number of minor components of other metals oxides. The oxides have a tendency to form metalhydroxide complexes in solution and the reactions of these oxides with water may be alkaline (CaO), acidic (SiO2) or amphoteric (MgO, Al2O3) [24]. Therefore, the Table 3 Use of Granulated Blast Furnace Slag (GBFS) and Furnace Bottom Ash (FBA) as a sorbent. Sorbent Sorbate
Treatment
Reference
GBFS
Basic Red Anionic dyes Cationic dyes Anionic and disperse dyes Phosphorus Heavy metals
Activated at 600 °C Activated at 400 °C Activated at 400 °C No treatment
Acidic dye
With hydrogen peroxide With hydrogen peroxide No treatment No treatment
Gupta et al. [5] Jain et al. [6] Bhatnagar and Jain [7] Ramakrishna and Viraraghavan [17] Kostura et al. [18] Nehrenheim and Gustafsson [19] Gupta et al. [20]
FBA
Indigo dye Reactive dyes Phosphorus
No treatment No treatment
Mittal et al. [21] Dincer et al. [22] Yan et al. [23]
dissociations of these complexes at the solid-solution interface leads to development of a positive or negative charge on the surface. In the case of net negative surface charge on GBFS, both dyes might be repelled because Acid Yellow 99 and Acid Red 183 are first dissolved in water and the sulfonate groups of dyes are converted to anionic dye ions (Fig. 1). Acid Yellow 99 and Acid Red 189 were sorbed by FBA and removal efficiencies from water were in the range of 30%–50% depending on initial dye concentrations even though no treatment was applied to FBA, i.e., it was only sieved and dried. The sorption dynamics and equilibrium isotherms of both dyes on FBA will be discussed in more detail in the following sections. Moreover, effects of operating parameters, such as, initial dye concentration, solution pH, ionic conductivity and temperature will be investigated. 3.2. Sorption mechanisms of dyes on FBA The pseudo first order, pseudo second order, Elovich and Weber– Morris rate equations were tested for the sorption of Acid Yellow 99 and Acid Red 183 by FBA. The related constants for each kinetic model were evaluated from the linear forms and are presented in Table 4. The evaluated correlation coefficients are presented in the table as well. It can be seen that the numerical values for the correlation coefficients are within acceptable limits and that they are higher than 0.85 for the pseudo first and the pseudo second order kinetics. The lowest value (0.51) was obtained for the Elovich rate equation. By looking at only the correlation coefficients, it could be said that the sorption mechanism of dyes onto FBA could be explained best by the pseudo second order kinetics. However, when the calculated qe values from models were compared with the experimental qe values (first row of Table 4), it could be concluded that both pseudo first and pseudo second order kinetics could explain the sorption mechanism of dyes on FBA quite effectively. In order to analyze sorption mechanisms, variations in dye uptakes (q) with time were determined experimentally. 1 L of dye solutions was prepared at the desired concentration in a glass flask and 10 g of FBA was added. The pH of dye solution was around 8 and no NaCl was added. Then the dye solutions was shaken and 10 mL samples were taken at 5, 15, 30, 45, 60, 90, 120, 150, 180, 240, 360, 480, 550, 1400, 1500, 1600 and 1800 min of adsorption. The residual dye concentrations in the samples were measured by spectrophotometer and the results were shown in Fig. 2. It can be seen that the sorption of both dyes is a very fast process and most of dye sorption on FBA was almost attained in the first 100 min. The q values can also be predicted from the studied kinetic models based on the numerical values presented in Table 4. For the sorption of Acid Yellow 99, the predictions of q values from the pseudo first order, pseudo second order and Elovich rate equations were presented in Fig. 3. The results have presented separately for 10 mg/L, 50 mg/L and 100 mg/L initial dye concentrations. The experimental q values were shown in the graphs as well which were evaluated from Eq. (1) using the numerical values presented in Fig. 2. Among the studied kinetic models, there is no doubt that the Elovich rate equation explains best the sorption of Acid Yellow 99 sorption onto FBA since the predicted q
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Table 4 Sorption kinetics constants. Co (mg/L)
Acid Yellow 99 10
Experimental qe (mg/g) Pseudo first order k1 (1/min) qe (mg/g) R2 Pseudo second order k2 (1/min) qe (mg/g) h (mg/g min) R2 Elovich equation a (mg/g min) b (g/mg) R2
0.8 3.3 × 10 0.60 0.99
Acid Red 183 50
100
2.1 −3
1.3 × 10 1.37 0.87
20
3.2 −3
50
0.5
1.0 × 10 2.64 0.85
−3
5.1 × 10 0.43 0.90
100
1.0 −3
1.7 × 10 1.06 0.92
0.6 −3
4.4 × 10− 3 0.40 0.89
0.03 0.66 0.01 0.97
0.04 1.17 0.06 0.99
0.01 1.40 0.03 0.91
0.01 0.54 4.30 × 10− 3 0.94
3.95 × 10− 3 0.83 2.72 × 10− 3 0.99
0.05 0.55 0.01 0.98
0.06 10.05 0.83
0.92 6.95 0.98
0.57 6.53 0.51
0.01 10.87 0.91
0.01 9.70 0.74
0.06 13.72 0.78
values are very close to experimental values. The predictions of q were overestimated by the pseudo second order kinetics model and the overestimation increases with an increase in the initial dye concentration. On the other hand, the predictions of q by the pseudo first order kinetics model were lower than the experimental values but the discrepancies were decreasing by the initial dye concentration. Similar observations were obtained for the sorption of Acid Red 183. Depending on the results obtained from Fig. 3, it could be concluded that the best kinetic model could not be decided only by looking at numerical values of the correlation coefficients. If the kinetic models are evaluated from their linear forms, it is best to check the evaluated model constants by using integral forms of the kinetic models. Especially for the pseudo first and pseudo second order kinetics, the qe values obtained from the intercept should be equal to the one obtained from the experiment. Dye molecules are large organic molecules and, therefore, the diffusion-controlled mechanisms can be important. Therefore, Weber–Morris intraparticle diffusion model has been tested. According to this model, the variations in Acid Yellow 99 uptakes on FBA were drawn with respect to the square root of time for 10 mg/L and 50 mg/L initial dye concentrations and the results are shown in Fig. 4. When the initial dye concentration was 10 mg/L, it was clear that the rate-controlling step was only the intraparticle diffusion and the surface adherence in the sorption ratelimiting step is negligible. The intraparticle rate constant (ki) was evaluated from the slope and was found to be 0.03 mg/g min0.5. On the other hand, as the concentration of dye increased to 50 mg/ L, the effects of surface hindrance on sorption rate increased since
the intercept changed from 0 to 0.6 even though ki stayed constant at 0.03 mg/g min0.5. 3.3. Adsorption isotherms The equations and evaluated constants for the Langmuir, Freundlich, Temkin and Dubinin–Radushkevich adsorption isotherms are presented in Table 5. All of the isotherms have different assumptions. Langmuir adsorption isotherm assumes that the adsorption sites are identical; each site retains one molecule of adsorbate, and all sites are energetically independent of the adsorbed quantity. On the other hand, the Freundlich adsorption isotherm assumes a heterogeneous surface with a non-uniform distribution of heat of adsorption. The Dubinin–Radushkevich isotherm explains the adsorption mechanism based on potential theory assuming heterogeneous surfaces as well. Temkin isotherm, however, assumes that binding energies of molecules are distributed uniformly and the heat of adsorption decreases linearly. For both dyes, it was not possible to represent the relation between dye uptakes and concentrations at equilibrium by using the Freundlich isotherm because negative KF values were obtained. However, it is not physically meaningful since adsorption capacity cannot be negative. For the sorption of Acid Red 183, only the Langmuir isotherm was within acceptable regression limits, i.e., correlation coefficient better than 0.8. In the case of the sorption of Acid Yellow 99, the Langmuir, Temkin and Dubinin–Radushkevich isotherms were calculated even though the correlation coefficient was very low for the Temkin
Fig. 2. Dye uptakes of FBA for different initial dye concentrations (pH: 8).
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A. Genc, A. Oguz / Desalination 264 (2010) 78–83 Table 5 Comparison of equilibrium isotherms. Equation
Isotherm constants
Acid Yellow 99
Acid Red 183
Langmuir
L aL C e qe = 1K+ aL C e
Freundlich
qe = KF Ce
Temkin
qe = bRT InðKTe Ce Þ
qe = qm Exp
2.45 0.14 0.94 Not possible 8.49 0.93 0.53 0.33 2.42 0.90
0.80 0.18 0.80 Not possible Not possible
Dubinin– Radushkevich
KL (mg/g) aL (L/mg) R2 KF n b (J/g) KTe (L/mg) R2 E (J/g) qm (mg/g) R2
1=n
Te
"
RT In 1 + −2E 2
1 Ce
2 #
Not possible
3.4. Effects of operating conditions
Fig. 3. Comparison of kinetic models predictions for the sorption of Acid Yellow 99 on FBA ((a) Co = 10 mg/L, (b) Co = 50 mg/L, (c) Co = 100 mg/L).
isotherm (0.53). When the numerical values of the Langmuir and Dubinin–Radushkevich isotherms constants (KL and qm) were compared, their predictions for the adsorption capacity of FBA were almost in the same order of magnitude. In addition, the magnitude of the second constant in the Dubinin–Radushkevich isotherm (E) was very small, which indicated that the adsorption energy is very low. This also suggests that the sorption of dyes onto FBA is a physical process and not a chemical reaction.
Fig. 4. Weber–Morris plots for the intraparticle transport of Acid Yellow 99.
Effects of initial dye concentrations on the sorption kinetics of Acid Yellow 99 and Acid Red 183 dyes onto FBA were studied by performing kinetic experiments at 10 mg/L, 50 mg/L and 100 mg/L dye concentrations and the results are presented in Fig. 3. For both dyes, the dye removal efficiencies decreased as the initial dye concentration increased. In addition, the removal efficiencies were very low when the initial dye concentration was 100 mg/L, where the maximum sorption capacity of FBA could be reached. In the comparison of both dyes, it was observed that the removal efficiencies for Acid Yellow 99 were always higher than the ones obtained for Acid Red 183. The dye removal efficiencies for Acid Yellow 99 were 53%, 44% and 15% for the three initial dye concentrations studied. On the other hand, the corresponding values for Acid Red 183 were 27%, 16% and 5%, respectively. When the structural formulas of both dyes are compared (Fig. 1) it can be observed that Acid Red 183 is a bigger molecule than Acid Yellow 99. Therefore, it could be much easier for Acid Yellow 99 to enter the pores of FBA. When both dyes were present in the solution, this effect was much clearer. For a constant total dye concentration, the dye removal efficiency of FBA increased more if the percentage of Acid Yellow 99 in the binary mixture of dyes increased. However, no such dependency was observed for Acid Red 183. It is very well known that pH is one of the important parameters in sorption studies [25] and, therefore, the sorption experiments for Acid Yellow 99 and Acid Red 183 dyes were repeated at different pH values by varying the initial dye concentrations. When the dyes were mixed with water, the solution pH was around 8–8.6. The batch equilibrium experiments were repeated under pH values of 4, 6 and 8 by adjusting pH with hydrochloric acid. The results showed that the increase of pH from 4 to 6 or 8 does not cause appreciable changes in dye uptakes by FBA. For example, when the initial dye concentration and pH were 60 mg/L and 4, the dye removal efficiencies for Acid Yellow 99 and Acid Red 183 were 44% and 17.3%, respectively. When the pH was increased to 8, the dye removal efficiency values changed to 49% and 15%, respectively. Similar results were observed for the other studied initial dye concentrations. The effects of ionic conductivity were investigated by adding NaCl (5 mg/L, 10 mg/L and 50 mg/L). It was observed that the addition of NaCl didn't cause any improvement in the sorption rate of both dyes; rather it caused slight decreases in the dye removal efficiencies. Increasing ionic conductivity could increase competition between ions for the sorption sites and therefore, the dye removals for both dyes could be reduced because they were ionic dyes in structure. The sorption experiments were performed at 20 °C and 40 °C and no appreciable change in the adsorbed quantity of dyes were observed over this temperature range. These results also suggest that the sorption of Acid Yellow 99 and Acid Red 183 are likely to
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be a physical diffusion process rather than a chemical reaction. This type of adsorption is likely classified as reversible and temperature dependence on adsorption would be comparatively weaker than desorption [26]. 4. Conclusions FBA and GBFS have been tested experimentally in the removal of two acid dyes (Acid Red 183 and Acid Yellow 99) from aqueous solutions. In the preparation of FBA and GBFS, they were only sieved by 250 μm opening mesh and no grinding was applied. Based on the experimental investigation and evaluated sorption kinetics, the following conclusions are drawn: - GBFS cannot be used as a sorbent for the removal of Acid Yellow 99 and Acid Red 183 from wastewater. - FBA can be used as an efficient sorbent for the removal of Acid Yellow 99 and Acid Red 183 from wastewater. Dye removal efficiencies can reach up to 50%. - The use FBA as a sorbent can be economical since no grinding is applied. - The sorption mechanisms of dyes on FBA are likely to be a physical diffusion process rather than a chemical reaction. - The rate-limiting step is found to be the intraparticle diffusion at lower dye concentration. As the dye concentration increases, the effect of surface hindrance on sorption rate is observed to increase. - The sorption mechanisms of Acid Yellow 99 and Acid Red 183 on FBA are found to be best described by the Elovich kinetic model. - The Langmuir isotherm gives the best fit for the sorption of Acid Yellow 99 and Acid Red 183 on FBA. - The dye removal efficiencies are not changed when pH is increased from 4 to 8. - Increasing temperature from 20 °C to 40 °C does not cause any improvements in the sorption of both dyes on FBA. - No effects of NaCl addition has been observed for the sorption of dyes on FBA. References [1] V.K. Gupta, Suhas, Application of low-cost adsorbents for dye removal — a review, J. Environ. Manage. 90 (2009) 2313–2342. [2] F. Fu, Y. Xiong, B. Xie, R. Chen, Adsorption of Acid Red 73 on copper dithiocarbamate precipitate-type solid wastes, Chemosphere 66 (2007) 1–7. [3] R.S. Juang, F.C. Wu, R.L. Tseng, The ability of activated clay for the adsorption of dyes from aqueous solutions, Environ. Technol. 18 (1997) 525–531.
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