Abstract

The focus of this study is the investigation of removal ability of methylene blue (MB) and malachite green (MG) dyes from aqueous solution by raw maize corncob (RMC) and H3PO4 activated maize corncob (AMC). Maize corncobs were carbonized at 500 °C for 2 h, and then impregnated at a phosphoric acid to maize corncob ratio of 2.5 g/g. The impregnated maize corncob was activated in a tubular vertical furnace at 450 °C for 2 h. Samples were characterized by different methods. Adsorption experiments were carried out as a function of solution pH, adsorbent dosage, contact time, initial concentration of dyes and the temperature. Experimental results show that the activation of maize corncob boosts four times the adsorption performance for the selected dyes. The adsorption process is very rapid and was pH dependent with high adsorption capacities in the basic range. The kinetic data were fitted with the pseudo-second-order kinetic model. The best fit of equilibrium data was obtained by the Langmuir model with maximum monolayer adsorption capacities of 75.27 and 271.19 mg/g for MB, 76.42 and 313.63 mg/g for MG, respectively, in the case of RMC and AMC. The temperature did not have much influence on the adsorption performance.

INTRODUCTION

Water is the most important raw material for human beings, animals, plants, and micro-organisms. Virtually all vital phenomena of the biosphere are related to the availability of water. Due to the rapid development in technology, water pollution is a major problem being faced by society today. The discharge of industrial, agricultural, and domestic wastewaters without treatment or with inadequate treatment level causes degradation of ecosystems (Vymazal 2014). The problem is even more serious in the case of industrial effluents which have a much more pronounced toxic nature.

Among industries consuming water in large quantities, the textile industry with that of tanneries came top of the list (Patterson 2012). The dyeing sector, and printing and finishing of textiles are of particular importance (Wang et al. 2011; Rosa et al. 2014). These activities generate a significant pollution in wastewater being highly loaded with acidic or basic dyes, salts, and adjuvants (Secondes et al. 2014). Disposal of these dyes has been extensively studied, with the processes used including precipitation (Zhu et al. 2007), ionic exchange (Greluk & Hubicki 2011), membrane filtration (Zylla et al. 2006), electrochemical destruction (Lin & Peng 1996; Brillas & Martinez-Huitle 2015), photodegradation (Barka et al. 2011b; Rosa et al. 2015; Morikawa & Shinohara 2016), and adsorption (Barka et al. 2006; Elmoubarki et al. 2015). Among these processes, adsorption is considered as a superior technique comparatively with other treatment methods due to the availability of many adsorbents, simplicity of design, high efficiency, and ability to treat dyes in a more concentrated form (Kanchi et al. 2013; Yagub et al. 2014).

Different sorbents have been conventionally used for the removal of dyes from aqueous solutions, whereas activated carbon has been widely used in the recent past due to the presence of different surface oxygen functional groups at its surface, its pore structure, and also for the high adsorption capacity (Titirici et al. 2012; Chen et al. 2013). The properties of the activated carbons depend on the activation process and the nature of the precursor (Herawan et al. 2013; Ranjithkumar et al. 2014). Several biomasses have been tested as precursors in the production of activated carbon, including buriti shells (Mauritia flexuosa L.) (Junior et al. 2014a), waste tea (Gokce & Aktas 2014), hazelnut husk (Karacetin et al. 2014), coconut shell (Isah et al. 2015), Diplotaxis harra (Tounsadi et al. 2015), macadamia nut endocarp (Macadamia integrifolia) (Junior et al. 2014b), olive stones (Hazzaa & Hussein 2015), chlorella-based algal residue (Chang et al. 2015), rice husk residue (Li et al. 2016), coconut shells and corn cobs (Ensuncho-Munoz & Carriazo 2014). However, studies in this field have not produced materials which meet all the demands of adsorption activity.

This work aims to evaluate the potential of maize corncob and H3PO4 activated maize corncob (AMC) as an economical and eco-friendly adsorbent for the removal of methylene blue (MB) and malachite green (MG) from aqueous solution. The materials were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and scanning electron microscopy (SEM). Several parameters that affect the adsorption including solution pH, adsorbent dosage, contact time, initial dye concentration and temperature were evaluated. Pseudo-first-order and pseudo-second-order kinetic models were tested to fit adsorption kinetic data. The equilibrium data were analyzed using Langmuir and Freundlich isotherm models.

EXPERIMENTAL

Materials

All the necessary chemicals used in this study were of analytical grade. MB and MG were provided by Sigma-Aldrich Chemicals and were used without further purification. HNO3 (65%) was purchased from Sharlau (Spain) and NaOH from Merck (Germany). The chemical formula and some other specific characteristics of these dyes are summarized in Table 1.

Table 1

Physicochemical characteristics of used dyes

Name Molecular structure MW (g/mol) λmax (nm) 
MB (Basic blue 9)  319.85 661 
MG (Basic green 4)  329.5 621 
Name Molecular structure MW (g/mol) λmax (nm) 
MB (Basic blue 9)  319.85 661 
MG (Basic green 4)  329.5 621 

Preparation of the adsorbents

Maize corncobs (locally obtained) were repeatedly washed with distilled water to remove dirt particles and were dried at 70 °C for 24 h. The dried corncobs were then powdered using a domestic mixer to particles of less than 160 μm in size. Ten g of the obtained raw maize corncobs (RMC) powder were carbonized at 500 °C for 2 h under nitrogen atmosphere. The obtained char was impregnated with phosphoric acid at a phosphoric acid to RMC ratio of 2.5 g/g for 6 h, followed by the removal of excess solution and overnight drying at 110 °C. The sample was further activated at 450 °C for 2 h. Subsequently, the cooled sample was repeatedly washed via hot deionized water to remove free phosphoric acid, tar, fines, and leachable matter followed by overnight drying at 110 °C. The obtained powder was powdered using a domestic mixer and sieved in particles of size lower than 125 μm using a normalized sieve. The obtained activated carbon was called AMC.

Characterization

The functional groups present at the surface of the RMC and AMC adsorbents were identified by FT-IR in the range of 4,400–400 cm−1 using a SCOTECH-SP-1 spectrophotometer. The samples were mixed with oven-dried spectroscopic grade KBr and pressed into a disk. XRD patterns were obtained using a Philips PW 1710 diffractometer equipped with a monochromatic Cu-Kα (1.541874Å). The diffraction patterns were recorded between 10 and 70 (2θ) degrees. The morphological characteristics of the RMC and AMC were analyzed by SEM using a FEI Quanta 200 model. A small amount of each sample was finely powdered and mounted directly on to an aluminum sample holder using a two-sided adhesive carbon model. The point of zero charge (pHPZC) was determined by the pH drift method according to the method proposed by Noh & Schwarz (1989). The pH of NaCl aqueous solution (50 mL at 0.01 mol/L) was adjusted to successive initial values in the range of 2.0–12.0 by addition of HNO3 (0.1 N) and/or NaOH (0.1 N). Moreover, 0.05 g of each adsorbent was added and stirred for 6 h. The final pH was measured and plotted against the initial pH. The pHPZC was determined at the value for which pHfinal = pHinitial.

Batch adsorption experiments

Adsorption experiments were performed in a series of 100 mL beakers containing the desired weight of each adsorbent and 50 mL of the dye solution at the desired concentration. These experiments were carried out at a constant agitation speed of 500 rpm by varying the pH of solution from 2 to 12, adsorbent dosage from 0.25 to 6 g/L, contact time from 5 to 300 min, initial dye concentration from 20 to 200 mg/L, and temperature from 10 to 50 °C. The solution pH was adjusted by adding NaOH (0.1 N) or HNO3 (0.1 N) and measured by a sensION+ PH31 pH meter. The temperature was controlled using a thermostatically controlled incubator.

After each adsorption experiment was completed, the solid phase was separated from the liquid phase by centrifugation at 3,000 rpm for 10 min. Determination of the concentration of the dyes was carried out by spectrophotometric analysis in the visible range at the wavelength of maximum absorption of each dye (Table 1). The adsorbed quantity was calculated using the following equation:  
formula
(1)
and the fading percentage/removal efficiency/adsorption efficiency:  
formula
(2)
where q (mg/g) is the adsorbed quantity, C0 (mg/L) is the initial dye concentration, C (mg/L) is the dye concentration at a time t, and R (g/L) is the mass of adsorbents per liter of solution.

RESULTS AND DISCUSSION

FT-IR analysis of the adsorbents

Figure 1 shows the FT-IR spectra of RMC and AMC. The spectra of the RMC sample shows a broad and strong band present between 3,600 and 3,200 cm−1, which can be assigned to the O–H stretching mode of hydroxyl groups and adsorbed water (Yakout & Sharaf El-Deen 2012). The position and asymmetry of this band at lower wave numbers indicate the presence of strong hydrogen bonds (from carbonyls, phenols, or alcohols). After activation, this band was separated into three more resolute bands; two bands at around 3,300 and 3,250 cm−1 are ascribable to vibrations of hydroxyl groups, whereas the position of the band for non-bonded alcohols, phenols, and carboxylic acids is usually around 3,500 cm−1. The band at 2,852 cm−1 for the raw corncob and not on activated corncob corresponds to the presence of –CH2 stretching of aliphatic groups. The bands at 1,630 cm−1 are characteristic of C = O stretching vibrations of ketones, aldehydes, lactones, or carboxyl groups. These bands become finer in the activated corncob. The bands between 1,590 and 1,400 cm−1 are usually ascribed to C = C vibrations, although some overlapping can be found with (O-H) around 1,450 cm−1. The bands about 1,030 cm−1 show the C–O–C stretching (alcohols, ethers, or phenols) and O–H deformation (Foo & Hameed 2011). These bands decreased by activation process as compared to the raw material.

Figure 1

FT-IR spectra of RMC and AMC adsorbents.

Figure 1

FT-IR spectra of RMC and AMC adsorbents.

XRD

The XRD patterns of RMC and AMC are shown in Figure 2. The XRD patterns of RMC exhibit broad peaks at 2θ = 17° indicating the amorphous part (i.e., cellulose, hemicellulose, and lignin) and at about 2θ = 22.5° denoting the partially crystallized portion of cellulose. The XRD patterns exhibit defined peaks and the absence of a broad peak in AMC reveals the predominantly amorphous structure of activated carbon. However, the occurrence of broad peaks at around 2θ = 17°, 22.5°, and 26° that are related to the (101) and (002) show signs of formation of a carbonaceous crystalline structure, and that results in better layer alignment (Liou & Wu 2009). This feature is evident because the samples have a turbostratic structure. This type of pattern is known to be characteristic of the carbon states described as clusters made of small fragments of graphene layers plus a certain amount of disorganized carbon.

Figure 2

XRD patterns of RMC and AMC samples.

Figure 2

XRD patterns of RMC and AMC samples.

Morphology of the adsorbents

SEM photographs of RMC and AMC are shown in Figure 3. The figure reveals significant differences between the surface morphology of the RMC and the prepared activated carbon (AMC). From the figure the absence of any well-defined pores on the surface of raw material can be seen. After activation, the pores wall were opened and the surface became smooth with many different size and shape cavities. The H3PO4 impregnation and activation temperature are effective in creating well-developed pores on the surface of the AMC. These new pores are formed due to the reaction between carbon and the activating agent. The development of porous structure results from the decomposition of the sample matrix by the impregnation followed by evaporation of tars during the heat treatment. The prepared activated carbon will have large adsorption capacity due to high porosity.

Figure 3

SEM images of RMC (a) and AMC (b).

Figure 3

SEM images of RMC (a) and AMC (b).

pH point of zero charge

The pHs of zero charge (pHPZC) of the adsorbents were found to be 6 and 3.5, respectively, for RMC and AMC. This result indicates that the adsorbents acquire a positive charge below a pH of 6 and 3.5, respectively, for RMC and AMC. Above these points, there is a net negative charge on the cell surface and the ionic state of functional groups at the surface of the adsorbents such as carboxyl, phosphoryl, sulfhydryl, and hydroxyl.

Effect of adsorbent dosage (R)

Figure 4 shows the effect of adsorbent dosage on the removal efficiency for MB and MG. The figure indicates that the adsorption yield increases with the increase in the adsorbent dosage and stabilizes at high adsorbent dosage. For RMC, the adsorption efficiency increased from 29.75 to 94.41% for MB and from 24.90 to 92.11% for MG when the adsorbent dosage increased from 0.25 to 4 g/L. For the AMC, the adsorption efficiency increased from 32.95 to 99.98% for MB and from 40.23 to 94.48% for MG when the adsorbent dosage was increased from 0.25 to 1 g/L. The observed enhancement in adsorption yield with increasing adsorbent dosage could be due to an increase in the number of possible binding sites and surface area of the adsorbents. A further increase in adsorbent dosage over 1 g/L for AMC and 4 g/L for RMC did not lead to a significant improvement in the adsorption yield. This may be due to the decrease in driving force for mass transfer at low concentration of dyes in solution (Barka et al. 2011a).

Figure 4

Effect of adsorbent dosage on the removal of MB and MG by RMC and AMC: C0 = 100 mg/L, contact time = 120 min, initial pH, T = 25 °C.

Figure 4

Effect of adsorbent dosage on the removal of MB and MG by RMC and AMC: C0 = 100 mg/L, contact time = 120 min, initial pH, T = 25 °C.

Effect of pH on the adsorption

Solution pH is a significant parameter which affects the dye adsorption process. It alters the surface charge of the adsorbents, the ionization state of dyes, as well as the structure of the dye molecules (Ai et al. 2011). Changes observed in the adsorption of MB and MG by RMC and AMC as a function of solution pH are presented in Figure 5. The figure indicates that as the pH increases, the adsorption capacities increase. This result may be due to a change in surface charge of both the dyes’ molecules and functional groups of adsorbent. The pHs of zero charge (pHPZC) of the adsorbents were found to be 6 and 3.5, respectively, for RMC and AMC. The pHPZC values indicate that the adsorbents acquire a positive charge below a pH of 6 and 3.5, respectively for RMC and AMC. At pH values above this point, there is a net negative charge on the cell surface and the ionic state of functional groups such as carboxyl, phosphoryl, sulfhydryl, hydroxyl, and amino. Consequently, the adsorbent–adsorbate interactions for the cationic dyes become progressively significant for larger pH values. We can conclude from this result that the negative surface charge of the activated carbon becomes greater with increasing pH.

Figure 5

Effect of solution pH on adsorption of MB and MG on RMC and AMC: C0 = 100 mg/L, contact time = 120 min, R = 1 g/L for RMC and 0.25 g/L for AMC, T = 25 °C.

Figure 5

Effect of solution pH on adsorption of MB and MG on RMC and AMC: C0 = 100 mg/L, contact time = 120 min, R = 1 g/L for RMC and 0.25 g/L for AMC, T = 25 °C.

Adsorption kinetics

The kinetic parameters, which are supportive for the prediction of adsorption rate and equilibrium time, provide important information for designing and modeling of the adsorption processes (Sivarajasekar & Baskar 2014a). The results of the study of the influence of contact time on the adsorption of MB and MG are presented in Figure 6. According to this figure, the adsorption rate increases rapidly at the beginning of the process and becomes slow with the increase in the contact time until equilibrium is reached. The equilibration times were found to be 120 min for RMC and 180 min in the case of AMC. In order to characterize the kinetics involved in the process of adsorption, pseudo-first-order and pseudo-second-order rate equations were proposed and the kinetic data were analyzed based on the regression coefficient (r2) and the amount of dye adsorbed per unit weight of each adsorbent.

Figure 6

Kinetics of MB and MG adsorption by RMC and AMC: C0 = 100 mg/L, R = 1 g/L for RMC and 0.25 g/L for AMC, pH = initial solution pH, T = 25 °C.

Figure 6

Kinetics of MB and MG adsorption by RMC and AMC: C0 = 100 mg/L, R = 1 g/L for RMC and 0.25 g/L for AMC, pH = initial solution pH, T = 25 °C.

The first-order rate expression of Lagergren based on solid capacity is generally expressed as follows (Lagergren 1898):  
formula
(3)
Integrating this equation for the boundary conditions t = 0 to t = t and q = 0 to q = qt, Equation (3) becomes:  
formula
(4)
where qe and q (both in mg/g) are, respectively, the amounts of metal adsorbed at equilibrium and at any time t (min), and k1 (1/min) is the rate constant of adsorption.
In contrast, the pseudo-second-order kinetic equation is based on the adsorption capacity which may be expressed in the form (Ho & Mckay 1999):  
formula
(5)
Integration of conditions with similar limits for the following equation gives:  
formula
(6)
where k2 (g/mg min) is the rate constant of pseudo-second-order adsorption.

Parameters of the pseudo-first-order and pseudo-second-order models were estimated with the aid of nonlinear regression. The obtained data and the correlation coefficients, r2, are given in Table 2.

Table 2

Kinetic parameters for the adsorption of MB and MG onto RMC and AMC

Adsorbent Dye qexp (mg/g) Pseudo-first-order
 
Pseudo-second-order
 
qe (mg/g) k1 (L/min) r2 qe (mg/g) k2 (g/mg min) r2 
RMC MB 61.20 60.82 0.0440 0.988 67.50 0.00840 0.992 
 MG 67.97 66.97 0.0713 0.969 71.95 0.00147 0.983 
AMC MB 180.53 166.44 0.0733 0.905 179.27 0.00062 0.960 
 MG 143.97 140.22 0.0989 0.991 150.42 0.00096 0.997 
Adsorbent Dye qexp (mg/g) Pseudo-first-order
 
Pseudo-second-order
 
qe (mg/g) k1 (L/min) r2 qe (mg/g) k2 (g/mg min) r2 
RMC MB 61.20 60.82 0.0440 0.988 67.50 0.00840 0.992 
 MG 67.97 66.97 0.0713 0.969 71.95 0.00147 0.983 
AMC MB 180.53 166.44 0.0733 0.905 179.27 0.00062 0.960 
 MG 143.97 140.22 0.0989 0.991 150.42 0.00096 0.997 

The table shows that the correlation coefficients for the pseudo-second-order kinetic model are closer to one than those of the Lagergren first order. From these results the adsorption can be estimated more appropriately by the pseudo-second-order kinetic model. These results reveal that boundary layer resistance was not the rate limiting step (Ho & Mckay 1998). The rate of dye adsorption may be controlled largely by a chemisorption process, in conjunction with the chemical characteristics of the adsorbents and the dyes (Eren & Acar 2006).

Equilibrium sorption

To optimize the design of an adsorption system for the removal of solutes by adsorbents, it is important to establish the most appropriate correlation for the equilibrium curves. Adsorption isotherm provides valuable information such as equilibrium sorption capacity and certain constants whose values express the surface properties and affinity of the adsorbent (Sivarajasekar & Baskar 2014b). Figure 7 represents the adsorption isotherms for MB and MG on RMC and AMC. The results show that the absorbed amount increases with the increase of the equilibrium concentration of the dye. This increase may be due to the high driving force for mass transfer. The isotherms forms were of the type H for RMC and L for AMC in Giles’ classification (Giles et al. 1974). In this study, the models of Langmuir and of Freundlich were used to describe the adsorption equilibrium.

Figure 7

Adsorption isotherms of MB and MG onto RMC and AMC: R = 1 g/L for RMC and 0.25 g/L for AMC, pH = initial solution pH, T= 25 °C, contact time = 120 min.

Figure 7

Adsorption isotherms of MB and MG onto RMC and AMC: R = 1 g/L for RMC and 0.25 g/L for AMC, pH = initial solution pH, T= 25 °C, contact time = 120 min.

Langmuir model

The most commonly used model is the Langmuir model (Langmuir 1918). The initial assumptions are that the solid adsorbent has a limited adsorption capacity, all active sites are identical, they can adsorb only one solute molecule (monolayer adsorption), and that there is no interaction between the adsorbed molecules. It means that once a dye molecule occupies a site, no further adsorption can take place on this site (Barka et al. 2012). The mathematical equation of Langmuir isotherm is expressed as follows:  
formula
(7)
where qe (mg/g) is the adsorbed amount at equilibrium, Ce (mg/L) is the equilibrium dye concentration (mg/L), KL is Langmuir equilibrium constant (L/mg), and qm the Langmuir maximum adsorption capacity (mg/g).

Freundlich model

The simple empirical Freundlich model is most commonly used. It is considered to be applicable to many cases, particularly in the case of multilayer adsorption interaction between the adsorbed molecules (Freundlich 1906). The Freundlich model equation is given as:  
formula
(8)
where kF (mg1−1/n/g/Ln) is the Freundlich constant and n is the heterogeneity factor. The KF value is related to the adsorption capacity; while 1/n value is related to the adsorption intensity.

Analysis of adsorption isotherms

The constants that characterize each of the above cited models were determined by nonlinear regression analysis. The obtained values are given in Table 3. The correlation coefficients (r2) are also presented in this table. The table indicates that the best correlation to experimental results was obtained with the Langmuir model. The maximum monolayer adsorption capacities were 76.42 and 313.63 mg/g for the MG in the case of RMC and AMC. 75.27 and 271.19 mg/g for the MB in the case of RMC and AMC, respectively. These results indicate that activation of the corncob increases extremely the adsorption of MB and MG. The activation of maize corncob boosts four times the adsorption performance for the selected dyes.

Table 3

Model isotherm constants for the adsorption of MB and MG onto RMC and AMC

  Langmuir
 
Freundlich
 
Dye Adsorbent qm (mg/g) KL (L/mg) r2 KF (mg1_1/n /g/Lnr2 
MB RMC 75.27 0.355 0.978 43.24 5.589 0.945 
AMC 271.19 0.042 0.955 44.06 2.887 0.882 
MG RMC 76.42 0.210 0.941 28.96 4.791 0.848 
AMC 313.63 0.006 0.937 4.32 1.293 0.926 
  Langmuir
 
Freundlich
 
Dye Adsorbent qm (mg/g) KL (L/mg) r2 KF (mg1_1/n /g/Lnr2 
MB RMC 75.27 0.355 0.978 43.24 5.589 0.945 
AMC 271.19 0.042 0.955 44.06 2.887 0.882 
MG RMC 76.42 0.210 0.941 28.96 4.791 0.848 
AMC 313.63 0.006 0.937 4.32 1.293 0.926 

In fact, another study based on various processes for the activation of corncob indicated little efficiencies for the adsorption of methyl orange (Hou et al. 2013). For further comparison with other materials, sorption capacities of MB and MG by several adsorbents studied in the literature are summarized in Table 4. It is obvious that RMC and AMC present greater sorption efficiencies than most organic and inorganic adsorbents previously studied. This study suggests that the RMC and AMC were more promising for an effective adsorption of MB and MG.

Table 4

Sorption capacities (mg/g) for different adsorbents

Adsorbents MB (mg/g) MG (mg/g) References 
Coal fly ash 16.6 – Wang et al. (2008)  
Sewage sludge 114.9 – Otero et al. (2003)  
Modified montmorillonite 322.6 – Wibulswas (2004)  
Spent activated clay 127.5 – Weng & Pan (2007)  
Bagasse fly ash – 42.18 Mall et al. (2005)  
Coconut shell – 214.63 Bello & Ahmad (2012)  
Functionalized attapulgite 207.48 – Zhang et al. (2015)  
Sepiolite 57.38 – Auta & Hameed (2012)  
Aerobic granules – 56.8 Sun et al. (2008)  
Beech sawdust – 83.21 Witek-Krowiak (2011)  
Raw maize corncobs (RMC) 75.27 76.42 This study 
AMC 271.19 313.63 This study 
Adsorbents MB (mg/g) MG (mg/g) References 
Coal fly ash 16.6 – Wang et al. (2008)  
Sewage sludge 114.9 – Otero et al. (2003)  
Modified montmorillonite 322.6 – Wibulswas (2004)  
Spent activated clay 127.5 – Weng & Pan (2007)  
Bagasse fly ash – 42.18 Mall et al. (2005)  
Coconut shell – 214.63 Bello & Ahmad (2012)  
Functionalized attapulgite 207.48 – Zhang et al. (2015)  
Sepiolite 57.38 – Auta & Hameed (2012)  
Aerobic granules – 56.8 Sun et al. (2008)  
Beech sawdust – 83.21 Witek-Krowiak (2011)  
Raw maize corncobs (RMC) 75.27 76.42 This study 
AMC 271.19 313.63 This study 

Effect of temperature

Figure 8 represents the variation of adsorbed amounts based on the temperature of the solution. From the figure we notice that the change in temperature has practically no influence on the adsorption efficiency. The observed trend could be due to the nature of the adsorbent particles. Increasing the temperature is known to increase the rate of the diffusion of molecules across the external boundary layer and the internal pores of the adsorbent particles, owing to the decrease in the viscosity of the solution. Therefore, changing temperature will change the equilibrium capacity of the adsorbent for a particular adsorbate.

Figure 8

Effect of temperature on the adsorption of MB and MG by RMC and AMC: C0 = 100 mg/L, R = 1 g/L for RMC and 0.25 g/L for AMC, pH = initial solution pH.

Figure 8

Effect of temperature on the adsorption of MB and MG by RMC and AMC: C0 = 100 mg/L, R = 1 g/L for RMC and 0.25 g/L for AMC, pH = initial solution pH.

CONCLUSIONS

This study has investigated MB and MG adsorption from an aqueous solution by RMC and H3PO4 AMC. The sorption characteristic has been examined using various sorption conditions. It was found that the sorption process was very rapid; the equilibrium time was obtained at 120 min for RMC and 180 min in the case of AMC. The sorption yield increases with the increase of sorbent dosage with an optimum at 1 g/L for RMC and 0.25 g/L for AMC. The optimum sorption was obtained at basic pH medium. Adsorption kinetics is better described by the pseudo-second-order model. The concentration of dye in the initial solution results in the increase of adsorption. The Langmuir model provides the best correlation of the experimental equilibrium data. The adsorption capacity was not influenced by temperature. Finally, these results show that AMC can be used as an efficient and economical adsorbent for the treatment of wastewaters containing synthetic dyes.

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