ADSORPTION OF ACID DYE ONTO ACTIVATED ALGERIAN CLAY

In this work, activated clay from Algeria was used as adsorbent for the removal of methyl orange (MO) from aqueous solution, for this, the effects of several parameters such as contact time, adsorbent dose, pH value of aqueous solution and temperature on the adsorption of MO were also studied. The results showed that nearly 30 min of contact time are found to be sufficient for the adsorption to reach equilibrium and the adsorption was favourable at lower pH. The acid dye concentration is measured with UV-visible spectrophotometer at a wavelength of 464 nm. The adsorption capacity of MO found to be 32.57 mg/g. The Pseudo-first-order and pseudo-second-order models were used to fit the experimental data. The adsorption kinetic process was found to follow a pseudo second order model.The Langmuir and Freundlich isotherms models were used to describe adsorption data, the results indicates that Langmuir and Freundlich models provide better correlation of the experimental data. The negative values of ΔG° at different temperatures show that the adsorption process is spontaneous. The values of ΔH and ΔS were found to be 1.04 kJ/mol and 3.35 J/mol.K, respectively. The positive value of ΔH confirms that the adsorption is endothermic and the adsorption process is chemical nature.


INTRODUCTION
Accumulation of dyes in wastewater from different industries such as dye synthesis, textiles, paper, cosmetics, printing, and plastics are one of the major sources of water pollution.These dyes are usually used in excess to make the dye better, and consequently sewage is highly concentrated with colorants.These dyes in surface waters are of barrier effect on the sun light penetration and aeration of water body, and thus reduce photosynthetic activity.Their removal from effluent by the use of conventional physico-chemical and biological processes is difficult [1] such as coagulation, ultra-filtration, electro-chemical adsorption and photo-oxidation, never the less these methods are not satisfying because of the weak colorant biodegradability [2][3][4].The activated carbon is the effective alternate for the concentration of dye ions even in the case of lower solute concentration.However activated carbon adsorption is limited due to the high cost of activated carbon and the cost involved in regenerating it.In this way the majority of the processes are very selective according to the colorant categories to treat and some just move the pollution instead of removing it [5].It is necessary for the process to mineralize the colorant.Adsorption technology has attracted interest in this context as an effective and alternative treatment process and has many advantages over the existing conventional process.This process is not only economic and feasible but also produces high quality of water [6].The different applications of the activated-clay depend on their specific adsorption properties, the ion exchange and the surface nature [7].Due to these qualities, clay is used in different field, like in medical and pharmaceutical industries, organic molecule polymerization [8] and pollutant retention such as pesticides, organic, inorganic compounds, heavy metals [9-10-11].The removal of methyl orange from wastewater needs great attention.The aim of this paper is to study the feasibility of using activated methyl orange and to determine the various parameters affecting sorption such as contact time, adsorbent dose, pH and temperature DRX and FTIR.Kinetic and isoth understand the organic colorant adsorption mechanisms [12].

Reagents and materials
The adsorbate (methyl orange MO) from Sigma-Aldrich.Having the chimical formula 327.33 g/mol , and λ max : 464 nm Figure 1.Molecular structure of methyl orange dye.
The adsorbent.We used a raw clay collected from the region of ''Tiout'', located in south Algeria.this last was dispersed hours in order to remove impurities.The suspension was then filtered and dried at 105 constant dry weight, then stored in a securely closed flask Acid-activated clay.A mass of 20 g of raw clay mL of sulfuric acid (0.25 M) at room temperature for 24 h.was filtered, washed several times with distilled water hours, in order to obtain dehydrated samples and a constant closed flask against the moisture.characterize the powder.

Characterization of the adsorbent
Chemical analysis showed the clay used is composed essentially of silica and approximately 71.5% and of iron oxide 7.30% (Table 1), the presence of ions Na in the clay gives it a swelling type.The ratio SiO characteristics it have both Bronsted and Lewis acid sites and when exchanged with cations having a high charge density, i clay and other MMT such as American and French.Raw clay from Tiout has 5.68% more Si than (Vienne, France) and 1.68% less SiO clay from Tiout contains 5.42% and 5.32% less A1 bentonites, respectively.
Qualitative analysis of Algerian clay is performed by FTI KBr pressed disc technique.The analysis was carried out on Perkin Elmer Spectrum One FT Spectrometer in the wave number range of 400 IR spectra of raw clay and activated clay notices the disappearance of the band that comes out around 2071 cm decrease in Fe 2 O 3 who owed to Fe study the feasibility of using activated-clay as an adsorbent for the removal of an anionic dye, methyl orange and to determine the various parameters affecting sorption such as contact time, adsorbent dose, pH and temperature were evaluated and the adsorbent was characterized by .Kinetic and isotherm adsorption models are performed in order to better understand the organic colorant adsorption mechanisms [12].

EXPERIMENTAL
The adsorbate (methyl orange MO).The dye used in this study is methyl orange, was purchased Having the chimical formula C 14 H 14 N 3 NaO 3 S and molecular weight of : 464 nm.The structure of this dye is shown in Figure 1.

Characterization of the adsorbent
Chemical analysis showed the clay used is composed essentially of silica and alumina approximately 71.5% and of iron oxide 7.30% (Table 1), the presence of ions Na + , Ca + and K in the clay gives it a swelling type.The ratio SiO 2 /Al 2 O 3 = 3.51 reveals its montmorillonite it have both Bronsted and Lewis acid sites and when exchanged with cations having a high charge density, in the other hand (Table 1) samaruzed diference between Algerian American and French.Raw clay from Tiout has 5.68% more Si than (Vienne, France) and 1.68% less SiO 2 than (Wyoming, USA), in the other hand the raw clay from Tiout contains 5.42% and 5.32% less A1 2 O 3 than the Wyoming and Vienne Qualitative analysis of Algerian clay is performed by FTIR transmission spectra using the KBr pressed disc technique.The analysis was carried out on Perkin Elmer Spectrum One FT Spectrometer in the wave number range of 400-4000 cm -1 .Figure 2 shows the characteristic FT and activated clay, their absorption band are given in (Table 2).notices the disappearance of the band that comes out around 2071 cm -1 will be explained by the who owed to Fe 3+ exchange by the H + protons from the sulfuric acid.
rbent for the removal of an anionic dye, methyl orange and to determine the various parameters affecting sorption such as contact time, were evaluated and the adsorbent was characterized by erm adsorption models are performed in order to better was purchased and molecular weight of used a raw clay collected from the region of ''Tiout'', located in south in distilled water and maintained under constant stirring for 2 impurities.The suspension was then filtered and dried at 105 o C to was treated under mechanical stirring with 200 The resulting acidic activated clay for a few then stored in a securely FTIR and DXR analysis techniques were employed to alumina and K + 3.51 reveals its montmorillonite it have both Bronsted and Lewis acid sites and when exchanged with cations n the other hand (Table 1) samaruzed diference between Algerian American and French.Raw clay from Tiout has 5.68% more SiO 2 than (Wyoming, USA), in the other hand the raw than the Wyoming and Vienne R transmission spectra using the KBr pressed disc technique.The analysis was carried out on Perkin Elmer Spectrum One FT-IR .Figure 2 shows the characteristic FT-, their absorption band are given in (Table 2).One will be explained by the The mineralogical composition of the natural clay and activated clay are determined by Xray diffraction (XRD) using DRX.D8 Advance Bruker generator with copper anticathode (λ CuKα = 1.5406Å).The X-ray spectrum shown in (Figure 3) that the raw clay is a mixture of monmorillonite and impuretes of calcite and quartz .underacid traitement all traces of calcite was removed in activated clay.centrifugation at 2500 rpm during 15 min.The quantity of MO adsorbed is determined with UVvisible spectrophotometer (Model Shimadzu 1240) at a wavelength of 464 nm.The equilibrium adsorption capacity q e (mg/g) was calculated from the following equation: q e is the amount of dye adsorbed at equilibrium (mg/g).C 0 and C e are the initial and equilibrium concentrations of the dye, respectively, computed from the calibration curve (mg/L).V is the volume of the solution (L) and m is the mass of the adsorbent (g).

Effect of contact time
The influence of contact time is achieved at natural pH of the solution for an initial concentration of 26.2 mg/L, with 80 mg/L of adsorbent at room temperature.The amount of dye adsorbed at time t was determined by the following expression: Where q t is the amount of dye adsorbed at time t (mg/L), C 0 and C t are the concentrations of the dye at initial (t = 0) and at time t, respectively.The results are shown in Figure 4.It can be noticed that the sorption is very fast and equilibrium between the aqueous solution and activated clay is established in less than 30 min.the mechanism of adsorbent removal can be described in migration of the dye molecule from the solution to the adsorbent particle and diffusion through the surface [13][14].The time of 30 min can be considered the saturation time.

Kinetics order
Many kinetic models have been applied to study the controlling mechanism of dye adsorption from aqueous solution.In order to investigate the adsorption processed of methyl orange on the adsorbent.The Pseudo-first-order model and the pseudo-second-order model were applied to fit the experimental data.The linear form of the pseudo-first-order model can be expressed by the following equation.
  e t e ln q q l t nq k    For the pseudo-second-order model is given by the following equation.
  Integrating the equation ( 4) for the boundary conditions t = 0 to t = t and q = 0 to q = q t , gives: Where q t is the amount of dye adsorbed (mg/g) at various time t, k (min −1 ) and k' (g/mg.min)are the adsorption rate constant, qe is the maximum adsorption capacity (mg/ g).The plot of ln(q e −q t ) versus t for the pseudo-first-order (not mentioned in this paper) is not linear for the adsorbent, this indicate that it is not appropriate to use the pseudo-first-order model to predict the adsorption kinetic of methyl orange dye onto activated clay.
The kinetic data obtained using the pseudo-second order indicates that the q e value calculated from the pseudo-second-order model is in accordance with the experimental q e value.The correlation coefficient R 2 of the linear plot is very high.The result is shown in Table 3.Several studies found that the kinetics of adsorption of dyes on clay supports obey to the pseudo-second-order [15][16][17][18].

Effect of adsorbent mass
The adsorption of MO on adsorbent was carried by preparing 50 mL dye solution for (26.2 mg/L) of dye concentration and varying the adsorbent dose (1 to 4 g/L) at room temperature for 30 min and at natural pH.The increase mass of adsorbent 1 g/L down to a value of 4 g/L causes a decreases in residual dye concentration.The increase in methyl orange adsorption with the increase in adsorbent mass is attributed to increase in surface area of micro pores and the increase in availability of vacant adsorption sites.Similar results have been reported by other authors [19][20].

Effect of pH
The pH is one of the most important factors controlling the adsorption of dye onto adsorbent.The influence of pH on dye removal was determined by performing the adsorption experiments at different initial pH of the solution (2-11) at room temperature.The pH had been adjusted to the desired value with HCl (0.1 M) and NaOH (0.1 M) solutions by using a HANNA 210 pHmeter equipped with a combined pH electrode.The adsorption of methyl orange onto activated Algerian clay is highly dependent on pH of the solution.
The Figure 6 shows, at lower pH more protons will be available causing an increase in electrostatic attractions between negatively charged dye anions and positively charged adsorption sites and causing an increase in dye adsorption.As the pH of the solution increases, the positive charge on the surface decreases and the number of negatively charged sites increases.A negative charged surface site on the clay does not favour the adsorption of anionic dye due to electrostatic repulsion.Also, in alkaline medium, there will be competition, between the OH − ions and the dye anions.Similar results have been reported for the adsorption of methyl orange on clay [21][22].

Effect of temperature
To observe the effect of temperature on the dye adsorption of MO by the activated clay, experiments are carried at different temperatures (20,30,40,50 and 60 o C) with 80 mg of adsorbent was added to 50 mL dye solution with constant initial dye concentration of 26.2 mg/L.The contents in the flasks were agitated for 30 min.The decrease in the adsorption capacity of methyl orange with increasing temperature results from the weakening of adsorptive forces between the active sites on the molecule dye and the adsorbed phase (Figure 7).Similar observations have been reported in the literature [23][24].

Thermodynamic parameters
The thermodynamics parameters studies free energy change (ΔG), enthalpy change (ΔH) and entropy change (ΔS) are the main thermodynamic characteristics of any adsorption system in equilibrium.The Gibbs energy G  is calculated from the given equation: k represented the ability of the retain of the adsorbate and extent of movement of it within the solution.The value of c k can be deduced from the following formula: Where q e is the amount of dye adsorbed at equilibrium (mg/g).C e is the equilibrium concentration of the dye in the solution.The thermodynamic equation: And the Van't Hoff equation: Can be deduced the following formula: The values of ∆ and ∆ can be obtained by plot of ln kc versus (1/T) are shown in Figure 10.Thermodynamic parameters for the adsorption of methyl orange on activated Algerian clay are given in Table 4.The negative values of ΔG for adsorbent at various temperatures indicate the process to be feasible and spontaneous.The positive value of ΔH confirms the endothermic nature of the adsorption process and indicates that the type of adsorption is chemical nature.The positive value of ΔS suggests randomness at the solid/liquid interface in the adsorption system increases during the adsorption process [25].

Adsorption isotherms and models
An adsorption isotherm is the presentation of the amount of solute adsorbed per unit weight of adsorbent as a function of the equilibrium concentration in the bulk solution at constant temperature.Langmuir and Freundlich adsorption isotherms are commonly used for the description of adsorption data.The Langmuir isotherm is valid for monolayer adsorption onto a surface with a finite number of identical sites.The homogeneous Langmuir adsorption isotherm is represented by the following equation.

 
Where q e is the amount adsorbed at equilibrium (mg/g), C e is the equilibrium concentration (mg/L), b is a constant related to the adsorption energy (L/mg), and q max is the maximum adsorption capacity (mg/g).The linear form of Langmuir equation may be written as: By plotting (1/q e ) versus C e ,q max andb can be determined if a straight line is obtained.The Freundlich isotherm is an empirical equation assuming that the adsorption process takes place on heterogeneous surfaces, and adsorption capacity is related to the concentration of colorant at equilibrium.The heterogeneous Freundlich adsorption isotherm is represented by the following equation: Where the K F is Freundlich constant related to the adsorption capacity (mg/g) and 1/n is indicative of the energy or intensity of the reaction and suggests the favourability and capacity of the adsorbent/adsorbate systems (L/mg).The linear form of Freundlich equation may be written as The values of and can be determined by plotting the log q e versus log C e , if a straight line is obtained.
The isotherm parameters for the adsorption of MO onto activated clay are summarised in Table 5.It can be seen, the result revealed that the adsorption of methyl orange dye onto activated clay was the best-fit both Langmuir and Freundlich isotherms.Furthermore, values of 1/n were between zero and one, which indicates that activated clay is favourable for the adsorption of MO dye under the experimental conditions employed [25].The comparison of adsorption capacities of various materials is given in Table 6.

CONCLUSION
The adsorption parameters of methyl orange onto the activated clay from aqueous solution have been evaluated in this study.The results showed that nearly 30 min of contact time are found to be sufficient for the adsorption to reach equilibrium and when the amount of activated clay increases from 1 g/L to a value of 4 g/L causes decreases in residual dye concentration.The value of kinetic constant and q e indicates that the adsorption follow the pseudo-second order model.The adsorption capacity of methyl orange onto activated clay decreases with increasing pH of the medium.The negative value of ∆G indicates that the adsorption is done through a spontaneous and favourable process; the positive value of ΔH confirms the endothermic nature of the adsorption process and indicates that the type of adsorption is chemical nature.The positive value of ΔS suggests randomness at the solid/liquid interface in the adsorption system increases during the adsorption process.The result revealed that the adsorption of methyl orange dye onto activated clay was the best-fit both Langmuir and Freundlich isotherms and the maximum adsorption capacity given by the Langmuir model was 32.3 mg/g at natural pH and at room temperature.

Figure 1 .
Figure 1.Molecular structure of methyl orange dye.used a raw clay collected from the region of ''Tiout'', located in south dispersed in distilled water and maintained under constant stirring for 2 impurities.The suspension was then filtered and dried at 105 then stored in a securely closed flask for use in the experiments.A mass of 20 g of raw clay was treated under mechanical stirring with sulfuric acid (0.25 M) at room temperature for 24 h.The resulting acidic activated clay washed several times with distilled water until SO 4 2-free, dried at 105 o C for a few hours, in order to obtain dehydrated samples and a constant weight, then stored in a securely closed flask against the moisture.FTIR and DXR analysis techniques were employed to

Figure 3 .
Figure 3. XDR result for raw and activated Algerian clay.Adsorption experimentsAdsorption experiments were carried out at room temperature (22 ±2 o C).Approximately 80 mg of activated clay was weighted into flask 100 mL of capacity and brought into contact with 50 mL of dye solution with predetermined initial dye concentrations C 0 .The adsorption tests are perfumed at natural pH and under constant magnetic stirring at 450 rpm during 30 min necessary time to reach adsorption equilibrium.The aqueous phase was separated by

Figure 4 .
Figure 4.The effect of contact time on the adsorption of MO onto activated clay.

4 Figure 5 .
Figure 5. Pseudo-second order kinetic plot for the adsorption of MO onto activated clay.

Figure 6 .
Figure 6.The effect of pH of the solution on the adsorption of MO onto activated clay.

Figure 7 .
Figure 7.The effect of the temperature on the adsorption of MO onto activated clay.

Figure 8 .
Figure 8. Plot of ln Kc versus 1/T for the estimation of thermodynamic parameters.

Table 1 .
Comparison of the composition (in %) of American, French, and Algerian clay.

Table 2 .
FTIR spectra data of raw and activated Algerian clay.
Figure 2b.FTIR spectra of natural Algerian clay.

Table 3 .
The pseudo-second-order parameters of MO adsorption into activated clay.

Table 4 .
Thermodynamic parameters of MO adsorption into activated clay.

Table 5 .
Isotherm constants for adsorption of methyl orange into activated clay.

Table 6 .
Comparison of the adsorption capacity of dyes onto adsorbents such as clay.