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Keywords:

  • rice husk;
  • adsorption;
  • malachite green;
  • kinetics;
  • thermodynamics

Abstract

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. EXPERIMENTAL
  5. RESULTS AND DISCUSSION
  6. CONCLUSIONS
  7. LITERATURE CITED

Low cost adsorbents from agricultural waste like rice husk was developed with various activation methods and tested for the removal of aqueous contaminants. Adsorption of a basic dye, malachite green (MG), from aqueous solution onto nitric acid treated (NRH), and peroxide treated rice husk (PRH) have been investigated. Various experiments were studied using batch adsorption technique under different conditions of pH, adsorbent dosage, initial dye concentration, and temperature. The adsorption capacities of MG by the NRH and PRH were essentially due to electrostatic forces. The NRH and PRH adsorbents had a relatively large adsorption capacity (18.1 and 26.6 mg/g). The adsorbent PRH had a higher surface charge at alkaline pH and enhanced removal of MG was obtained under alkaline conditions. Typical adsorption kinetics indicated the pseudo second-order kinetics behavior. The adsorption isotherms obeys Langmuir isotherm model. It was observed that the rate of adsorption improves with increasing temperature and the process is endothermic nature. The negative value of the change in Gibbs free energy (ΔG°) indicates that the adsorption of MG on PRH and NRH is feasible and spontaneous. © 2013 American Institute of Chemical Engineers Environ Prog, 33: 38–46, 2014


INTRODUCTION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. EXPERIMENTAL
  5. RESULTS AND DISCUSSION
  6. CONCLUSIONS
  7. LITERATURE CITED

Waste water disposed by various textile and paper industries is a major hazard to the environment and drinking water due to the presence of a large number of contaminants like acids, bases, dissolved solids, and colors [1]. According to an estimate more than 100,000 commercially available dyes with over 7 × 105 tonnes of dyestuff are produced and used annually. Treatment processes for dye-contaminated waste streams include chemical precipitation, membrane filtration, ion exchange, carbon adsorption, and coprecipitation/adsorption [1-7]. Malachite green (MG) is a popular dye, which is also called aniline green, benzaldehyde green, or china green, which is effective against fungi and gram-positive bacteria. MG is widely used as a direct dye for silk, wool, jute, leather, dye cotton, aquaculture as a parasiticide, food, health, textile, and other industries like fish breeding industry for control the fungus saprolegnia, which infects fish eggs in commercial aquaculture [8]. Several countries have banned using this dye due to carcinogenic, genotoxic, mutagenic, and teratogenic properties. It is still being used in many countries due to its low-cost, availability, and lack of a proper alternative [9-11].

Adsorption on activated carbon (AC) was highly efficient for the removal of various impurities/pollutants from wastewater; however, the production cost and the regenerability of AC inhibits its large-scale application as an adsorbent. Therefore, there is a need to develop low cost ACs for the effective removal of various pollutants from wastewater such as heavy metals, dyes, pesticides, and other organic pollutants [1, 5-7, 11]. In this context, agricultural byproducts are good source of adsorbents for the removal of various pollutants from wastewater due to the availability and low cost.

Rice husk possesses a granular structure, is insoluble in water, and has chemical stability and high mechanical strength, making it a good adsorbent material for treating various wastes from water and wastewater. The chemical components of rice husk ash are found to be SiO2, H2O, Al2O3, Fe2O3, K2O, Na2O, CaO, and MgO. Rice husk may facilitate the adsorption of heavy metals and other pollutants because of irregular morphology and its heterogeneous chemical nature [12].

In this perspective rice husk, which is an agro-based waste, has emerged as a valuable source for the utilization in the wastewater treatment. Rice husk is extensively used in rural India, because of its widespread availability and relatively low cost. The annual generation of rice husk in India is ∼18–22 million tons [12]. The rice husk, as a commodity waste, can also be made into AC, which is used as an adsorbent in the wastewater treatment. Rice husk are accounting for approximately one-fifth of the annual gross of rice in the world (545 million metric tons) [13]. Thus the aim of this study was to develop ACs from rice husk and to test the performance for the removal of MG dye from aqueous solution. The effect of different parameters such as contact time, initial dye concentration, temperature, and pH were analyzed. The equilibrium data of the adsorption process were then analyzed to study the adsorption isotherms of MG from its aqueous solution.

EXPERIMENTAL

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. EXPERIMENTAL
  5. RESULTS AND DISCUSSION
  6. CONCLUSIONS
  7. LITERATURE CITED

Adsorbate

MG oxalate, N-[4-[[4-(dimethylamino)phenyl]phenylmethylene]-2,5-cyclohexadien-1-ylidene]-Nmethyl-oxalate (MG), molecular formula C52H54N4O12 was obtained from S. D. Fine-Chem Limited, Mumbai, India. The chemical structure of MG is shown in Figure 1. In this experiment, 100 mg/L stock solution was prepared by dissolving a known amount of dye salt in doubly distilled water and further dilutions were made to get particular concentration of dye in the batch experiments. All other reagents used were of analytical grade. Experiments were conducted to study the adsorbent capacity by varying the pH, temperature, adsorbent dosage, and adsorbate concentration etc.

image

Figure 1. Chemical structure of malachite green.

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Preparation of Activated Carbon

Rice husk utilized in the present study was obtained from local rice mills. The starting materials were washed with deionized water, dried at 100°C for 48 h in an oven. These dried materials were placed in a furnace and carbonized at 900°C under N2 flow for 5 h. For all experiments the flow rate of inert gas and heating rate was fixed at100 mL/min and 10°C/min and after treatment samples were cooled to room temperature under nitrogen (N2) flow the sample was taken in to a crucible and digested for 30 min with 50:50 (v/v %) of 69% HNO3/30% H2O2, and the samples were wrapped with aluminum foil. Then the sample was kept at 400°C for 10 min followed by several washings with distilled water. Then the sample was dried at 120°C. The samples were named as NRH (nitric acid treated rice husk) and PRH (peroxide treated rice husk). These samples were stored in separate airtight containers free from moisture until further use.

Characterization of the Adsorbent

Physical properties such as specific surface area, pore volume distribution were measured using the nitrogen gas adsorption technique using a surface area analyzer (Quantachrome Nova 2200) with liquid nitrogen at 77 K. The surface area was calculated using the BET method. Prior to the experiment, the samples were out-gassed at 523 K for 3 h. Oxygen containing functional groups formed as a result of activation were characterized by temperature programmed decomposition (TPD) at He atmosphere (50 mL min−1, ramp 10°C min−1) in the range 298–1173 K using a Quantachrome gas sorption analyzer. The surface composition of the AC samples were measured by XPS (VG Scientific ESCA Lab 210 spectrometer) using a monochromated AlKα radiation as the excitation source. Morphological changes were observed with a scanning electron microscope (SEM) (JOEL-JSM6610LV) whereas the surface roughness was estimated on atomic force microscope (AFM) (VEECO) using the tapping mode.

Adsorption Studies

Various batch adsorption tests were carried out in 100 mL of dye solution with NRH/PRH adsorbent at a constant temperature of 300 K. The experiments were carried out to investigate the effects of initial MG concentration (10–30 mg/L), adsorbent dosages (100–200 mg). The experiment performed by changing one of the parameters at a time while the other parameters were fixed. The MG content in solution before and after adsorption was measured by UV/visible spectrophotometer (T90 + UV/VIS Spectrometer, PG Instruments, UK) at it maximum wavelength of 615 nm. The concentration retained in the adsorbent phase (qe, mg/g) and percentage of removal were calculated by using Eqs. (1) and (2)

  • display math(1)
  • display math(2)

where C0 and Ce are the MG concentrations at initial state and at equilibrium (mg/L), respectively, V is the volume of solution in L, W is the weight of adsorbent (g), and C is the solution concentration at the end of the adsorption process (mg/L).

Effect of Physical Parameters on MG Adsorption

To study the effect of contact time and initial concentration on the MG uptake, 100 mL of MG solutions with initial concentration of 10–30 mg/L were prepared in a series of 250 mL beakers. Two hundred milligram of the NRH/PRH was added into each beaker and the beakers were then placed on a magnetic stirrer at constant temperature of 303 K, with constant speed of rotation up to 90 min with a fixed time intervals (15 min). The effect of temperature on the MG adsorption process was examined by varying the adsorption temperature from 303, 313, 323, and 333 K by adjusting the temperature controller of the water bath shaker. The effect of solution pH on the MG adsorption process was studied by varying the initial pH of the solution from 2 to 11. The pH of the solutions was maintained by hydrochloric acid–potassium chloride for the range of pH 2, Potassium hydrogen phthalate–sodium hydroxide for the range of pH 4, borax–sodium hydroxide for the range of pH 9 and sodium hydrogen carbonate–sodium hydroxide for pH 11 [14] and was measured using pH meter (Model Systronic Digital pH meter-335, India). The MG initial concentration was fixed at 30 mg/L with adsorbent dosage of 200 mg/100 mL and the temperature was 303 K.

Kinetic Studies

Kinetic studies were carried out with a known amount of NRH/PRH and 100 mL of dye solution taken in a 250 mL beaker. The beakers were then kept on a magnetic stirrer with constant stirring at ambient temperature. After a fixed time interval (15 min), the adsorbent was separated by centrifugation, and the centrifugate thus obtained was analyzed spectrophotometrically to determine the equilibrium concentration of the dye. The kinetic studies were also carried out at different adsorbate concentrations.

RESULTS AND DISCUSSION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. EXPERIMENTAL
  5. RESULTS AND DISCUSSION
  6. CONCLUSIONS
  7. LITERATURE CITED

Physicochemical Studies of the Support

The summary of the physicochemical properties of carbons studied in this paper is shown in Table 1. As seen in Table 1, the nitric acid treatment at high temperature results slightly higher surface area than peroxide treatment. SEM pictures (Figures 2a and 2b) confirm the presence of inter particle porous network, whereas, AFM images (Figures 2c and 2d) confirm the increase in the surface roughness after treatment.

image

Figure 2. Morphology of the adsorbent (a) SEM for untreated carbon, (b) SEM for PRH, (c) AFM for untreated carbon, and (d) AFM for PRH. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]

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Table 1. Physicochemical properties of PRH and NRH.
Characterization methodResults
NRHPRH
Temperature programmed decompositionSurface oxygen-containing groups 4.46 mmol g−1surface oxygen-containing groups 11.15 mmol g−1
CO = 3.21 (mmol g−1)CO = 3.62 (mmol g−1)
CO2 =1.25 (mmol g−1)CO2 = 7.52 (mmol g−1)
BET N2-adsorptionBET surface area 330 (m2/g)BET surface area 300 (m2/g)
Micropore surface area 193 (m2/g)Micropore surface area 190 (m2/g)
External surface area 137(m2/g)External surface area 113 (m2/g)
Micropore volume 0.163 (ml/g)Micropore volume 0.143 (ml/g)
X-ray photoelectron spectroscopyRelative surface atomic concentrations ofRelative surface atomic concentrations of
C = 61.4C = 26.3
O = 35.1O = 72.6
N = 3.5N = 1.1

Effect of Initial Dye Concentration and Contact Time

It is well-known that the dye concentration plays as an important role in the adsorption process, which can impel strongly the solute molecules to overcome mass transfer resistance between the liquid and the solid phases [15]. Figures 3a and 3b show the effect of different initial dye concentrations (10–30 mg/L) on the adsorption capacity of NRH and PRH, respectively. As seen from the Figure 3 the percentage of adsorption decreases with increasing initial concentrations of dye for both NRH and PRH. Moreover, the PRH had the capacity to remove up to 90% even for a concentrated solution of 30 ppm. Almost 75% dye removal was observed for 30 ppm with NRH.

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Figure 3. Effects of initial concentration on amount of MG adsorbed at different contact times (experimental conditions: adsorbent dosage 200 mg/100 mL, temperature 303 K and natural initial pH without adjustment) (a) NRH and (b) PRH. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]

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Figure 3 also shows that the initial dye concentration has a marked effect on the contact time necessary to reach adsorption equilibrium. It can be found that a rapid uptake occurred for the initial concentration 10 mg/L, where over 85% of dye can be removed with PRH and 70% of dye can be removed with NRH within 45 min. Whereas, for the initial concentration of 20 and 30 mg/L, a relatively slow dye uptake can be observed and took 75 min to reach 85% removal with PRH and 70% removal with NRH. At low concentration, the ratio of dye molecules to the number of available adsorption sites on adsorbent may be limited and consequently the adsorption process may mainly occur on the exterior surface of AC. The rate of adsorption is fast in this stage, resulting in short time. With an increase in the amount of dye molecules, the situation changes and lots of dye molecules are probably adsorbed by the interior surface of adsorbent by pore diffusion after the adsorption of the exterior surface reaches saturation. Similar discussion has been reported by Hameed et al. for studying adsorption processes for methylene blue [16].

Effect of Temperature

Temperature is an important parameter for adsorption processes. It has significant influence on the adsorption of MG on NRH and PRH. The effect of temperature was investigated in the temperature range 303–333 K. The experimental results shows that the removal of MG increased by increasing the temperature from 303 to 333 K (Figures 4a and 4b). Most adsorption processes are governed by exothermic processes [17], but the present system is governed by endothermic adsorption [18].

image

Figure 4. Effect of temperature in the removal of MG on (a) NRH and (b) PRH (experimental conditions: adsorbent dosage 200 mg/100 mL and natural initial pH without adjustment). [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]

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Effect of Adsorbent Dosage

To understand the effect of adsorbent dosage and initial concentration, the adsorbent dosage varied between 100 and 200 mg during MG initial concentration varied between 10 and 30 mg/L and the typical results are shown in Figure 5. As expected, an increase in adsorbent dosage leads to an increase in the percentage removal of MG. Initially, a rapid enhancement of dye removal was observed with increasing the dosage from 100 to 200 mg. As the adsorbent dosage increases, the adsorbent sites available for the dye molecules also increase and consequently better adsorption [15].

image

Figure 5. Effect of adsorbent dosage on adsorption of MG. (experimental conditions: adsorbent dosage 200 mg/100 mL, temperature 303 K and natural initial pH without adjustment). [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]

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Effect of pH

The pH of the solution plays as an important factor in the adsorption process, which may alter the surface properties of the adsorbent as well as the degree of ionization of the dye. The influence of pH on the dye adsorption onto NRH and PRH was studied for the dye concentration (30 mg/L) and amount of adsorbent (200 mg/100 mL) in the pH range of 2–11 and the results are shown in Figures 6a and 6b, respectively. Clearly, both the amount adsorbed and the percentage removal efficiency of MG on adsorbent increased as the pH of aqueous solution increased from 2 to 11. MG is a cationic basic dye as denoted by the presence of the positive nitrogen ion in its structure. On dissolution, the oxalate ion enters the aqueous solution ensuring that the dye has an overall positive charge. In carbon-aqueous systems the potential of the surface is determined by the activity of H+ ions, which react with the carbon surface. For the carbon surface the potential determining ions are H+ and OH and complex ions formed by bonding with H+ and OH. The broken bonds along the surface of the carbon result in hydrolysis.

image

Figure 6. Effect of solution pH on MG adsorption on (a) NRH and (b) PRH (experimental condition: adsorbent dosage 200 mg/100 mL, initial concentration 30 mg/L and temperature 303 K). [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]

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At low pH

  • display math

At high pH

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In our studies the rate of adsorption is high at higher pH. With the increase of pH value, the negative charge increases on the surface of adsorbent and the surface will then exhibit a cation exchange capacity [19, 20].

Adsorption Isotherms

The adsorption isotherm for the removal of MG was studied using an adsorbent dosage of between 100 mg/100 mL and 200 mg/100 mL at an initial concentration varied between 10 mg/L and 30 mg/L. The adsorption equilibrium data are conveniently represented by adsorption isotherms, which correspond to the relationship between the mass of the solute adsorbed per unit mass of adsorbent (qe) and the solute concentration for the solution at equilibrium (Ce).

Langmuir Adsorption Isotherm

The Langmuir adsorption isotherm has been traditionally used to quantify the performance of different adsorbents. The data obtained were then fitted to the Langmuir adsorption isotherm [21] applied to equilibrium adsorption assuming that adsorption energy is constant and independent of surface coverage where the adsorption occurs on localized sites with no interaction between adsorbate molecules and that maximum adsorption occurs when the surface is covered by a monolayer of adsorbate. The linear form of Langmuir isotherm is represented as Eq. (3).

  • display math(3)

where Ce (mg/L) is the equilibrium concentration of the MG, qe (mg/g) is the amount of MG adsorbed per unit mass of adsorbent. Qm (mg/g) and KL (L/mg) are Langmuir constants related to adsorption capacity and rate of adsorption, respectively. A linear plot of Ce/qe versus Ce in Figure 7 was employed to determine the value of Qmax (mg/g) and KL (L/mg) from slope and intercept, respectively. The data obtained with the correlation coefficients (R2) was listed in Table 2.

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Figure 7. Langmuir isotherm for MG adsorption onto PRH and NRH (experimental conditions: adsorbent dosage 200 mg/100 mL, dye concentration = 30 mg/L and natural initial pH without adjustment). [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]

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Table 2. Estimated parameters of Langmuir isotherms for adsorption of 30 mg/L MG on PRH and NRH at an adsorbent dosage of 200 mg/100 mL
Langmuir-isotherm constantsPRHNRH
303 K313 K323 K333 K303 K313 K323 K333 K
Qm (mg g−1)8.011.412.914.223.737.138.8610.9
KL (L mg−1)0.4581.0882.0264.4780.1390.3300.5411.168
R20.9930.9960.9990.9990.9920.9940.9950.998
RL0.06220.02610.01420.00640.17950.08110.05110.0243

Weber and Chakraborti [22] expressed the essential characteristics and the feasibility of the Langmuir isotherm in terms of a dimensionless constant separation factor or equilibrium parameter (RL), which can be defined as Eq. (4).

  • display math(4)

where C0 is the highest initial solute concentration whereas RL value implies whether the adsorption is unfavorable (RL > 1), linear (RL = 1), favorable (0 < RL < 1), or irreversible (RL = 0) [23]. Table 2 shows that all the RL values obtained were between 0 and 1, showing that the adsorption of MG on the PRH and NRH was favorable at the experimental conditions. The lower the RL value, the more irreversible the adsorption process. As the temperature increases from 303 to 323 K in PRH, the RL values were as well found to decrease, indicating that the adsorption was more favorable at higher temperature and also PRH is better adsorbent than NRH. Langmuir isotherm equation proved that the surface of PRH and NRH for adsorption of MG is made up of homogeneous adsorption than heterogeneous adsorption [24], which is in agreement with previous reports that the Langmuir model gave a better fit than other models on the adsorption using different adsorbents [25, 26]. This suggested that some homogeneity on the surfaces or pores of the activated adsorbents may have played an important role in MG adsorption.

Kinetic Modeling

The kinetic study of adsorption processes provides useful data regarding the efficiency of the adsorption and the feasibility for large scale operations. To understand the adsorption process of MG onto NRH/PRH, the kinetic models such as the linearized form of first order, second order, pseudo first order, pseudo second order, elovich adsorption kinetic model, and intra particle diffusion models given in Eqs. (5)(10), respectively were used to determine the mechanism of adsorption process [27]. The equations are represented as

  • display math(5)
  • display math(6)
  • display math(7)
  • display math(8)
  • display math(9)
  • display math(10)

where Kf is the first order rate constant in min−1, Ks is the second order rate constant in mg/g/min, tq is adsorbed quantity at time t (mg/g), K1ad is the pseudo-first-order rate constant in min−1, K2ad is the pseudo-second-order rate constant in mg/g/min, α and β are the simple elovich kinetic constants, kd is the intraparticle diffusion rate constant (mol/g min−1/2) and t is time in min.

These parameters were evaluated from the linear plots of ln [c]/[c0] versus t, 1/[C] versus t, ln(qeqt) versus t, t/qt versus t, ln‘t’ versus qt and qt versus √t, respectively. The correlation coefficient (R2) calculated from these plots was used to evaluate the applicability of these models. The analysis of the correlation coefficients shown in Table 3 suggests that the experimental data fit the pseudo second order model that indicates that the adsorption of MG ions on the surface of NRH/PRH is chemical adsorption. Similar discussion has been reported by Hameed and El-Khaiary, for studying adsorption processes for MG [28] and Mane et al., for studying adsorptive removal of brilliant green [29].

Table 3. Kinetic constants for first order, second order, pseudo first order, pseudo second order, and elovich kinetic models for adsorption of 30 mg/L MG on PRH and NRH at an adsorbent dosage of 200 mg/100 mL.
Kinetic modelParametersPRHNRH 303 K
303 K313 K323 K
First orderKf (min−1)0.0090.010.010.006
R20.6140.8090.9120.930
Second orderKS (g mg−1 min)0.0020.0030.0030
R20.9750.9850.7810.983
Pseudo first orderK1ad (min−1)0.0140.0160.0180.018
qe (mg/g)9.2906.5922.93823.281
R20.8500.6620.4190.914
Pseudo second orderK2ad (min−1)0.0110.0220.0670.037
qe (g mg−1 min)15.3816.1316.1327.03
R20.9980.9970.9990.992
Simple elovichα0.8750.9070.9480.895
β0.0620.0510.0460.040
R20.8100.6620.5650.935

The intraparticle diffusion was also involved for adsorption of MG onto NRH/PRH as shown in Figure 8. Previous studies showed that such plots may present a multilinearity, which indicates that two or more steps occur. The first sharper portion is the external surface adsorption or instantaneous adsorption stage. The second portion is the gradual adsorption stage, where the intraparticle diffusion is rate limited. The third portion is final equilibrium stage, where the intraparticle diffusion starts to slow down due to extremely low concentration in the solution [30]. The diffusion model plot shown in Figure 8 suggests two stage adsorption process, surface adsorption and intraparticle diffusion. The first portion of the plot indicates boundary layer effect, i.e., surface adsorption while the second linear portion is due to the intraparticle/pore diffusion within the pores of the carbon [31]. The slope of the linear portion indicated the rate of the adsorption. The lower slope corresponds to a slower adsorption process. Figure 8 shows that the slope of the first portions (1.495 and 2.144 for NRH and PRH, respectively) is greater than second portions (0.593 and 0.387 for NRH and PRH, respectively) and also confirms that slope of the PRH is greater than NRH, hence it may be conclude that the uptake is initially faster and then slows down. It is likely that initially the adsorbate is transported to the macropores and mesopores and then it is slowly diffused into micropores [32] and also extremely low dye concentration left in the solution [31]. These suggest that in the adsorption of MG over the AC was controlled by external mass transfer followed by intra particle diffusion mass transfer.

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Figure 8. Intraparticle diffusion kinetic model for MG adsorption on PRH and NRH (experimental conditions: adsorbent dosage 200 mg/100mL, Dye concentration = 30 mg/L, temperature = 303 K and natural initial pH without adjustment). [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]

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The NRH and PRH adsorbents used in this work have a relatively large adsorption capacity (18.1 and 26.6 mg/g) when compared to other adsorbents reported in the literature shown in Table 4. This indicates that NRH and PRH are effective for the removal of MG from aqueous solutions. Similarly Rahman et al., and Lakshmi et al., reported that the AC derived from rice husks produced by thermal–chemical process gives an effective adsorbent for removal of organic dyes [11, 33].

Table 4. Comparison of adsorption capacities of various adsorbents for malachite green dye.
Adsorbent(qe) (mg/g)References
NRH18.1Present study
PRH26.6Present study
Hen feather10.3[34]
Acid activated low cost carbon9.74[35]
Arundo donax root carbon8.70[36]
Activated carbons, commercial grade8.27[37]
Rice husk7.40[38]
Bentonite clay7.72[39]
Neem sawdust4.35[40]
Tamarind fruit shell1.951[41]
Activated charcoal0.179[42]

Thermodynamic Study

Experiments were conducted at different temperatures (303, 313, 323, and 333 K). The thermodynamic parameters, namely, change in standard enthalpy (ΔH°), standard entropy (ΔS°), and standard Gibbs free energy (ΔG°) for the present system, were determined using following expressions [43, 44].

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  • display math(12)
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where and Cac (mg/L) is the amount adsorbed on the surface of the adsorbent at equilibrium, Ce is the equilibrium concentration of MG in the solution (mg/L), R (8.314 kJ/mol K) is the universal gas constant and T (K) is the absolute temperature. The values of Kc increased by increasing the temperature, which indicates an endothermic nature of the process of removal. The thermodynamic parameters were determined from Figure 9 and given in Table 5. The values of Gibbs free energy change (ΔG°) changed from −2349.65 to −7559.28 J mol−1 and −5298.04 to −7837.77 J mol−1 for NRH and PRH adsorbents, respectively when increasing the temperature from 303 to 333 K. The negative values of the ΔG° indicate the spontaneous adsorption process and the positive values of the standard enthalpy change (ΔH°) for the intervals of temperature were further indication of the endothermic nature of the adsorption process, and the positive values of ΔS° for the corresponding temperature intervals suggest the probability of favorable adsorption [45].

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Figure 9. Determination of thermodynamic parameters (experimental conditions: adsorbent dosage 200 mg/100 mL, dye concentration = 30 mg/L and natural initial pH without adjustment). [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]

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Table 5. Thermodynamic parameters for the adsorption of 30 mg/L MG on PRH and NRH at an adsorbent dosage of 200 mg/100 mL.
S. noT (K)ΔG° J/molΔH° (J/mol)ΔS° (J/K mol)
NRH
1303−2349.6551,003.89179.06
2313−4878.81
3323−5989.13
4333−7559.28
PRH
1303−5298.0426,177.46103.426
2313−5396.28
3323−6290.25
4333−7837.77

CONCLUSIONS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. EXPERIMENTAL
  5. RESULTS AND DISCUSSION
  6. CONCLUSIONS
  7. LITERATURE CITED

The present study revealed that acid treated AC derived from rice husk can be used as a low-cost adsorbent for the removal of dyes from aqueous solution. The adsorption was high under alkaline conditions. As the adsorbent dosage increased, high removal was observed, and the adsorption capacity increased with temperature. The experimental data fitted well in the Langmuir isotherms and pseudo second order kinetic model. The negative ΔG° values in the range 303–333 K confirmed the spontaneity of adsorption, whereas, positive ΔH° and suggest that the adsorption of MG onto NRH and PRH was endothermic. From this study, it may be concluded that PRH is a better adsorbent than to nitric acid treated one, which may be attributed because of more number of functional groups on PRH, as confirmed by physical–chemical studies.

LITERATURE CITED

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. EXPERIMENTAL
  5. RESULTS AND DISCUSSION
  6. CONCLUSIONS
  7. LITERATURE CITED
  • 1
    Gupta, V.K., Mittal, A., Krishnan, L., & Gajbe V. (2004). Adsorption kinetics and column operations for the removal and recovery of malachite green from wastewater using bottom ash. Seperation and Purification Technology, 40, 8796.
  • 2
    Fenglian, F., Liping, X., Bing, T., Qi, W., & Shuxian, J. (2012). Application of a novel strategy-advanced fenton-chemicalprecipitation to the treatment of strong stability chelated heavymetal containing wastewater. Chemical Engineering Journal, 189–190, 283287.
  • 3
    Almutairi, F.M., Williams, P.M., & Lovitt, R.W. (2012). Effect of membrane surface charge on filtration of heavy metal ions in the presence and absence of polyethylenimine. Desalination Water Treatment, 42, 131137.
  • 4
    Zhang T., Wang Y., Ng J., & Sun D.D. (2012). A free-standing, hybrid TiO2/K-OMS-2 hierarchical nanofibrous membrane with high photocatalytic activity for concurrent membrane filtration applications. RSC Advances, 2, 36383641.
  • 5
    Rajgopal, S., Karthikeyan, T., Prakash Kumar, B.G., & Miranda, L.R. (2006). Utiliza-tion of fluidized bed reactor for the production of adsorbents in removal of malachite green. Chemical Engineering Journal 116, 211217.
  • 6
    Garg, V.K., Kumar, R., & Gupta, R. (2004). Removal of malachite green dye from aqueous solution by adsorption using agro-industry waste: A case study of Prosopis cineraria. Dyes Pigments, 62, 110.
  • 7
    Gong, R., Jin, Y., Chen, F., Chen, J., & Liu, Z. (2006). Enhanced malachite green removal from aqueous solution by citric acid modified rice straw. Journal Hazardous Material, 137, 865870.
  • 8
    Srivastava, S., Sinha, R., & Roy, D. (2004). Toxicological effects of malachite green. Aquatic Toxicology, 66, 319329.
  • 9
    Chang, C.F., Yang, C.H., Shu, Y.O., Chen, T.I., Shu, M.S., & Liao, I.C. (2001). Effects of temperature, salinity and chemical drugs on the in vitro propagation of the Dinoflagellate parasite, Amylodinium cellatum. Asian Fishries Society, P31.
  • 10
    Schnick, R.A. (1988). The impetus to register new therapeutants for aquaculture. Progressive Fish Culturist, 50, 190196.
  • 11
    Rahman, I.A., Saad, B., Shaidan, S., & Sya Rizal, E.S. (2005). Adsorption characteristics of malachite green on activated carbon derived from rice husks produced by chemical–thermal process. Bioresource Technology, 96, 15781583.
  • 12
    Ahmaruzzaman, M., & Gupta, V.K. (2011). Rice husk and its ash as low-cost adsorbents in water and wastewater treatment. Industrial and Engineering Chemistry Research, 50, 1358913613.
  • 13
    Lashkenari, M.S., Davodi, B., & Eisazadeh, H. (2011). Removal of arsenic from aqueous solution using polyaniline/rice husk nanocomposite. Korean Journal of Chemical Engineering 28, 15321538.
  • 14
    Zhang, L., Li, C., Ding, L., Xu, K., & Ren, H. (2011). Influences of initial pH on performance and anodic microbes of fed-batch microbial fuel cells. Journal of Chemical Technology and Biotechnology, 86, 12261232.
  • 15
    Almeida, C.A.P., Debacher, N.A., Downs, A.J., Cottet, L., & Mello, C.A.D. (2009). Removal of methylene blue from colored effluents by adsorption on montmorillonite clay. Journal of and Colloid Interface Science, 332, 4653.
  • 16
    Hameed, B.H., Din, A.T.M., & Ahmad, A.L. (2007). Adsorption of methylene blue onto bamboo-based activated carbon: Kinetics and equilibrium studies. Journal of Hazardous Material, 141, 819825.
  • 17
    Gupta, V.K., & Suhas, (2009). Application of low-cost adsorbents for dye removal: A review. Journal of Environmental Management, 90, 23132342.
  • 18
    Kauspediene, D., Kazlauskiene, E., Gefeniene, A., & Binkiene, R. (2010). Comparison of the efficiency of activated carbon and neutral polymeric adsorbent in removal of chromium complex dye from aqueous solutions. Journal of Hazardous Material 179, 933939.
  • 19
    Gong, R., Sun, Y., Chen, J., Liu, H., & Yang, C. (2005). Effect of chemical modification on dye adsorption capacity of peanut hull. Dyes Pigments, 67, 175181.
  • 20
    Baskaran, P.K., Venkatraman, B.R., & Arivoli, S. (2011). Adsorption of malachite green dye by acid activated carbon-kinetic, thermodynamic and equilibrium studies. Journal of Chemistry, 8, 918.
  • 21
    Langmuir, I. (1918). The adsorption of gases on plane surfaces of glass, mica and platinum. Journal of American Chemical Society, 40, 13611403.
  • 22
    Weber, T.W., & Chakraborti, R.K. (1974). Pore and solid diffusion models for fixed bed adsorbents. Journal of American Institute of Chemical Engineers, 20, 228238.
  • 23
    McKay, G., Blair, H.S., & Gardener, J.R. (1982). Adsorption of dyes on chitin. I. Equilibrium studies. Journal of Applied Polymer Science 27, 30433057.
  • 24
    Tunc, O., Tanac, H., & Aksu, Z. (2009). Potential use of cotton plant wastes for the removal of Remazol Black B reactive dye. Journal of Hazardous Material, 163, 187198.
  • 25
    Tabak, A., Baltas, N., Afsin, B., Emirik, M., Caglar, B., & Eren, E. (2010). Adsorption of reactive red 120 from aqueous solutions by cetylpyridinium-bentonite. Journal of Chemical Technology and Biotechnology 85, 11991207.
  • 26
    Yuan, X., Shi, X., Zenga, S., & Weia, Y. (2011). Activated carbons prepared from biogas residue: Characterization and methylene blue adsorption capacity. Journal of Chemical Technology and Biotechnology, 86, 361366.
  • 27
    EI-Ashtoukhy, E.S.Z., Amin, N.K., & Abdelwahab, O. (2008). Removal of lead (ii) and copper (ii) from aqueous solution using pomegranate peel as a new adsorbent. Desalination, 223, 162173.
  • 28
    Hameed, B.H., & El-Khaiary, M.I. (2008). Equilibrium, kinetics and mechanism of malachite green adsorption on activated carbon prepared from bamboo by K2CO3 activation and subsequent gasification with CO2. Journal of Hazardous Material, 157, 344351.
  • 29
    Mane, V.S., Mall, I.D., & Srivastava, V. Ch. (2007). Kinetic and equilibrium isotherm studies for the adsorptive removal of brilliant green dye from aqueous solution by rice husk ash. Journal of Environmental Management, 84, 390400.
  • 30
    Cheung, W.H., Szeto, Y.S., & McKay, G. (2007). Intraparticle diffusion processes during acid dye adsorption onto chitosan. Bioresource Technology, 98, 28972904.
  • 31
    Mitali, S., Kumar, A.P., & Bhasker, B. (2003). Modeling the adsorption kinetics of some priority organic pollutants in water from diffusion and activated energy parameters. Journal of Colloidal and Interface Science, 266, 2832.
  • 32
    Arinjay, K., Shashi, K., & Surendra, K. (2003). Adsorption of resorcinol and catechol on granular activated carbon: Equilibrium and kinetics. Carbon 41, 30153025.
  • 33
    Lakshmi, U.R., Srivastava, V.Ch., Mall, I.D., & Lataye D.H. (2009). Rice husk ash as an effective adsorbent: Evaluation of adsorptive characteristics for Indigo Carmine dye. Journal of Environmental Management, 90, 710720.
  • 34
    Mittal, A. (2006). Adsorption kinetics of removal of a toxic dye, malachite green, from wastewater by using hen feathers. Journal of Hazardous Material 133, 196202.
  • 35
    Hema, M., & Arivoli, S. (2008). Adsorption kinetics and thermodynamics of malachite green dye unto acid activated low cost carbon. Journal of Applied Science and Environmental Management, 12, 4351.
  • 36
    Zhang, J., Li, Y., Zhang, C., & Jing, Y. (2008). Adsorption of malachite green from aqueous Solution onto carbon prepared from Arundo donax root. Journal of Hazardous Material, 150, 774782.
  • 37
    Mall, I.D., Srivastava, V.C., Agarwal, N.K., & Mishra, I.M. (2005). Adsorptive removal of malachite green dye from aqueous solution by bagasse fly ash and activated carbon kinetic study and equilibrium isotherm analyses. Colloids Surface A 264, 1728.
  • 38
    Chowdhury, S., Mishra, R., Saha, P., & Kushwaha, P. (2011). Adsorption thermodynamics, kinetics and isosteric heat of adsorption of malachite green onto chemically modified rice husk. Desalination, 265, 159168.
  • 39
    Tahir, S.S., & Rau, N. (2006). Removal of a cationic dye from aqueous solutions by adsorption onto bentonite clay. Chemosphere, 63, 18421848.
  • 40
    Khattri, S.D., & Singh, M.K. (2009). Removal of malachite green from dye wastewater using neem sawdust by adsorption. Journal of Hazardous Material 167, 10891094.
  • 41
    Saha, P., Chowdhury, S., Gupta, S., Kumar, I., & Kumar, R. (2010). Assessment on the removal of malachite green using tamarind fruit shell as biosorbent. Clean-Soil, Air, Water, 38, 437445.
  • 42
    Iqbal, M.J., & Ashiq, M.N. (2007). Adsorption of dyes from aqueous solutions on activated charcoal. Journal of Hazardous Material, B 139, 5766.
  • 43
    Sharma, Y.C. (2008). Thermodynamics of the removal of cadmium by adsorption on indigenous clay. Chemical Engineering Journal, 145, 6468.
  • 44
    Tian, Y., Liu, P., Wanga, X., & Lin, H. (2011). Adsorption of malachite green from aqueous solutions onto ordered mesoporous carbons. Chemical Engineering Journal, 171, 12631269.
  • 45
    Sharma, Y.C. (2011). Adsorption characteristics of a low-cost activated carbon for the reclamation of colored effluents containing malachite green. Journal of Chemical and Engineering Data, 56, 478484.