Removal of Anionic Dye by Natural Algerian Montmorillonite

The use of synthetic chemical dyes in various industrial processes, such as food, paper, plastic, textile, etc. are one of the most problematic water pollution causes [1]. Discharge of wastewater into natural streams and rivers from the industries using dyes poses severe environmental problems because they are usually very recalcitrant to microbial degradation. Dyes in surface waters are of barrier effect on the sun light penetration and aeration of water body, and thus reduce photosynthetic activity [2]. For these reasons, several methods are used for eliminating the excess of colored organic pollutants from process or wastes effluents including biological treatments, however, unsatisfactory results were achieved by these techniques, such as coagulation-flocculation based on the addition of coagulant and flocculants (aluminium salts and polymers) [3], but coagulation generates chemical sludge and doesn’t remove acid and reactive dyes of low molecular weight Biological treatment may involve aerobic and anaerobic degradation by microorganisms [4], Adsorption using activated carbon or ion exchange resins is the most popular technique for dyes removal due to its efficiency but the activated carbon cannot adsorb dispersed and pigmented, dyes nevertheless these methods are not satisfying because of the weak colorant biodegradability [5,6]. Other new processes electro coagulation, advanced oxidation processes,, and adsorption were elaborated to meet the required standards. Among these techniques, adsorption is considered as the most efficient technology for the removal of dyes using local materials.


Introduction
The use of synthetic chemical dyes in various industrial processes, such as food, paper, plastic, textile, etc. are one of the most problematic water pollution causes [1]. Discharge of wastewater into natural streams and rivers from the industries using dyes poses severe environmental problems because they are usually very recalcitrant to microbial degradation. Dyes in surface waters are of barrier effect on the sun light penetration and aeration of water body, and thus reduce photosynthetic activity [2]. For these reasons, several methods are used for eliminating the excess of colored organic pollutants from process or wastes effluents including biological treatments, however, unsatisfactory results were achieved by these techniques, such as coagulation-flocculation based on the addition of coagulant and flocculants (aluminium salts and polymers) [3], but coagulation generates chemical sludge and doesn't remove acid and reactive dyes of low molecular weight Biological treatment may involve aerobic and anaerobic degradation by microorganisms [4], Adsorption using activated carbon or ion exchange resins is the most popular technique for dyes removal due to its efficiency but the activated carbon cannot adsorb dispersed and pigmented, dyes nevertheless these methods are not satisfying because of the weak colorant biodegradability [5,6]. Other new processes electro coagulation, advanced oxidation processes,, and adsorption were elaborated to meet the required standards. Among these techniques, adsorption is considered as the most efficient technology for the removal of dyes using local materials.
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. It is necessary for the process to mineralize the colorant. Recent investigations by several researchers proved onto use of low-cost, reusable, locally available, biodegradable adsorbent made from natural sources like waste orange peel, banana with cotton waste, rice husk, agriculture waste residues and bentonites clay [7]. The different applications of the clay depend on their specific adsorption properties, the ion exchange and the surface nature [8]. Due to these qualities, clay is used in different field, like in medical and pharmaceutical industries, organic molecule polymerization [9,10], and pollutant retention such as pesticides, organic, inorganic compounds, heavy metals [11].
The originality of this present work is to compare the performance and capacity of adsorption of methyl orange from different clays. Indeed, we propose to evaluate the removal efficiency of methyl orange in aqueous solution by adsorption using raw Algerian MMT clay. The essential parameters of the adsorption process, mainly contact time,

Abstract
Adsorption of methyl orange (MO) using an Algerian montmorillonite has been investigated. Which was used for the first time like an adsorbent for removing anionic dye from aqueous solution, the influences of several parameters such as contact time, adsorbent dose, pH and temperature on the adsorption of methyl orange have been tested. The results showed that nearly 40 min of contact time are found to be sufficient for the adsorption to reach equilibrium. The residual concentration of the dye is determined using UV/Vis Spectrophotometer at wavelength 464 nm. Langmuir and Freundlich isotherm models were used to describe adsorption data. Adsorption kinetics was best described by the pseudo-second order model. mass of clay, temperature, initial concentration of dye, and pH of the aqueous solution were determined and optimized. The equilibrium of adsorption was modelled by using the Langmuir and Freundlich isotherm models, the kinetic parameters and intra-particle diffusion were also then determined for the methyl orange -Algerian MMTsystem.

Materials Preparation of MMT clay
The clay used in this work is montmorillonite (MMT) type from Tiout region, this last was suspended in distilled water and maintained under constant stirring for 2 hours to release impurities. The suspension was then filtered and dried at 105°C to constant dry weight, then stored in a securely closed flask against the moisture.

Dyes
In order to show the Algerian MMT clay capacity of decoloration, we chose an organic colorant that it has methyl orange is an intensely colored compound used in dyeing and printing textiles. It is also known as C.I. Acid Orange, dye was purchased from Sigma Aldrich, heterocyclic aromatic chemical compound, having the chimical formula C 14 H 14 N 3 NaO 3 S and molecular weight of 327.33 g/mol. The structure of direct dye was given in Figure 1.

Characterization of MMT clay
Chemical analysis showed the clay used is composed essentially of silica and alumina approximately 71.5% and of iron oxide 7.30% , Chemical compositions in mass % of raw clay obtained are listed in 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 characteristics 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 MMT and other MMT such as American and French. Raw clay from Algerian has 5.68% more SiO 2 than (Vienne, France) and 1.68% less SiO 2 than (Wyoming, USA), in the other hand the Algerian MMT contains 5.42% and 5.32% less A1 2 O 3 than the Wyoming and Vienne bentonites, respectively.
Qualitative analysis of Algerian MMT is performed by FTIR transmission spectra using KBr technique. The analysis was carried out on Perkin Elmer precisely Spectrum One FT-IR Spectrometer in the wave number range of 400-4000 cm −1 . The FTIR spectrum of TN clay was showed in Figure 2 and the FT-IR results are represented in Table 2.
The mineralogical composition of the montmorillonite was performed on by X-ray diffraction (XRD) using DRX.D8 ADVANCE (BRUKER) X-Ray powder diffractrometer operanting with Kα radiation of Cu (λ = 1,5406 Å), and 2θ ranging from 2° to 80°. The Xray spectrum shows that the Algerian raw clay is a mixture of monmorillonite and impuretes of calcite and quartz ( Figure 3).

Adsorption experiments
Adsorption experiments were carried out at room temperature (22 ± 2°C). Approximately 80 mg of Algerian montmorillonite (MMT) was weighted into 100 ml glass containers and brought into contact with 50 ml of dye solution with predetermined initial dye concentrations C 0 . The obtained suspensions were maintained under constant magnetic stirring during the necessary time to reach adsorption equilibrium. The adsorption tests are perfumed at natural pH, room temperature and stirring at different time intervals. After equilibrium, the aqueous phase was separated by centrifugation. The concentration of the residual dye was determined using a UV-Vis spectrophotometer (SHIMADZU 1240) at 664 nm. The adsorption equilibrium capacity (q e ) (mg/g) was calculated from the following equation:   Table 2: FTIR spectra data of raw Algerian clay.
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 (mg/l).
V: is the volume of the solution (l). m: is the mass of the adsorbent (g).

Effect of contact time
The influence of time is achieved at natural pH of the solution for an initial dye concentration 26.186 mg/l, with 80 mg/1 of raw clay and room temperature. The amount of colorant adsorbed q t 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. Figure 4 shows the time course of adsorption equilibrium of methyl orange onto raw clay. The amount of dye adsorbed by adsorption on raw clay was found to be rapid at the initial period between (0-40 min) of contact time and then become slow and stagnant with increase in contact time (40-180 min). This was due to the fact that, at the initial stage the number of free adsorption sites was higher, and the slow adsorption rate in the later stage was due to slower diffusion of solute into the interior of the adsorbent [12,13]. The maximum adsorption occurred after 60 min and there was almost no adsorption beyond this time.

Kinetics order
The kinetic studies describe the rate of adsorption and this rate controls the equilibrium time. These kinetic models are useful for the design and optimization of effluent treatment models. Pseudo first order, pseudo second order, The second order kinetic model has the following formula.
( ) Where k is the rate constant of second-order adsorption has the following formula.
For the pseudo-second-order model is given by the following equation.
( ) Where ' k is the rate constant of pseudo-second-order adsorption has the following formula.
The kinetic data obtained using the second order and pseudosecond order is depicted in Figures 5 and 6. 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. The value of kinetic constant and q e indicates that the adsorption follow the pseudo-second order model. Several studies found that the kinetics of adsorption of dyes on clay supports obey to the pseudo-second-order [14][15][16][17].

Effect of adsorbent mass
The effect of adsorbent dosage on the adsorption process can be carried out by preparing adsorbent-adsorbate solution with different amount of adsorbents (1-4 g/l) added to fix initial dye concentration (26.186 mg/l), room temperature, pH natural and shaken together until equilibrium time. The effect of sorbent quantity on dye removal is illustrated in Figure 7. From the figure it can be seen that an increase mass of crude clay 1g /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 for the adsorption of methyl orange on Algerian MMT [18][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 N) and NaOH (0.1 N) solutions by using a HANNA 210 pH-meter equipped with a combined pH electrode. The adsorption of methyl orange onto clay is highly dependent on pH of the solution. Figures 8 and 9 shows the influence of the pH of the initial dye solution on the adsorption capacity of MO on Algerian MMT. As the pH value increased from 2.0 to 6.0, the adsorption capacity of dye onto Algerian MMT rapidly decreased. The removal dye is higher in the acid pH region because the MO acid dye give negatively charged ions when dissolved in water, the adsorption of MO dye is facilitated on positively charged surface of sorbent at pH < pHpzc.
In contrast, at a high pH solution the capacity of dye removal will decrease for anionic dye adsorption [21]. Because when the pH of dye solution is increased the surface tends to acquire negative charge, thereby resulting in a decreased adsorption of dyes due to decreasing electrostatic force existing between the negatively charged sorbate and positively charged sorbent.

Effect of temperature
The amount of dye adsorbed on Algerian MMT was determined at 20, 30, 40 and 60°C to investigate the effect of temperature. 80 mg of adsorbent was added to 50 ml dye solution with initial concentration of 26.186 mg/l. The contents in the flasks were agitated for 40 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 and the Algerian MMT anion of the dye, but also between the molecules dye and the adsorbed phase [22].

Thermodynamic parameters
The Gibbs energy G ∆ is calculated from the given equation: Kc represented the ability of the retain of the adsorbate and extent of movement of it within the solution. The value of Kc can be deduced from the following formula: Where: q e : is the amount of dye adsorbed at equilibrium (mg/g)
According to the thermodynamic parameters represented in Table  4 we realized that the ∆H enthalpy of the system is negative so the adsorption process on Algerian MMT is exothermic, the low value of the enthalpy ΔH energy (<20 Kj/mole) shows that it is a physical adsorption, the physic sorption is generally considered to be an effective method for quickly lowering the concentration of dissolved dyes in an effluent, Adsorption takes place in multilayer, The negative values of ΔG° for Algerian MMT adsorbent at various temperatures indicate the process to be feasible and spontaneous. Actually that the values of the ΔG° decrease with increasing temperature shows the increase of spontaneous influence [23].

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 the equilibrium concentration (mg/l), b a constant related to the adsorption energy (l/mg), and q max 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 and b 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: 1 n e e F q C K = ⋅ (14) 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 values of K F and 1 n can be determined by plotting the log e q versus log e C , if a straight line is obtained.
The isotherm parameters for the adsorption of MO onto Algerian MMT are summarised in Table 5. It can be seen, the result revealed that the adsorption of methyl orange dye onto Algerian MMT was the bestfit both Langmuir and Freundlich isotherms.
Furthermore, values of 1/n were between zero and one, which indicates that Algerian MMT is favourable for the adsorption of MO   Benguella and Yacouta-Nour [18] Jiang et al.

Chakkrit Umpuch and
Songsak Sakaew In this study dye under the experimental conditions employed [24]. The comparison of adsorption capacities of various materials is given in Table 6.