Journal of Chemical Engineering & Process Technology
Open Access

Adsorption Isotherm of Methylene Blue Dye on Groundnut Shell and Sorghum Husk

Kyauta Sunday^* and Erugo Immaculate Amarachi ^*Correspondence: Kyauta Sunday, Department of Chemical Engineering, Abubakar Tafawa Balewa University, Bauchi, Nigeria, Email:

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Abbreviation

MB: Methylene Blue dye; GS: Groundnut Shell; SH: Sorghum Husk; UV: Ultraviolent spectrophotometer

Introduction

The released voluminous amount of toxic substances in to the water system has afected the human beings as well as aquatic animals. Dyes are used extensively in various industries such as textiles rubbers plasticss printings leathers cosmeticss etc., and also in production of colored products. Dyes affect the penetration of sunlight into the water bodies and thus interfere with the growth of bacteria and hinder photosynthesis in aquatic plant. It poses a serious threat to mankind and water qualitys thereby is a matter of vital concern. It causes acute and chronic efects on exposure to human skins such as allergics dermatitiss skin irritations cancers mutation etc. It is very difficult to separate dye from water by using conventional techniques [1]. Among the various treatment methods adsorption processs chemical coagulation flocculation degradation process etc. have been explored to remediate these dyes in the waste water [2]. Among the various techniques available for its remediation adsorption technique has been proved to be most efective process. Adsorption is preferred over other processes due to possible regeneration and recovery of the sorbet.

Adsorption is a unit operation process which refers to attachment of molecules of liquid or gas on the surface solid substance. It is based on the fact that some solids preferentially adsorb other solute from the solution onto their surfaces. Dyes are particularly removed using various adsorbents. Many such adsorbents have been explored for its removal. However in this research work we considered adsorption process using groundnut shell and sorghum husk.

Problem statement

The world is becoming more industrialized therefore the amount of toxic material (e.g. dye) released in to the environment is becoming highs some agricultural by-product can be used for water purification so as to comply with the environmental regulation.

Aim and objective

The aim of the research work is to study the adsorption isotherm for methylene blue dye on groundnut shell and sorghum husk.

The objectives of the research work are:

• To determine the adsorption isotherm that best fits the batch adsorption data.
• To determine values of Langmuirs freunlish and Temkin constants which defined the adsorption process.

Scope

The research is limited to the adsorption of methylene blue dye using groundnut shell and sorghum husks and the isotherm model used are Langmuirs Freundlich and Temkin isotherm.

Justification

Massive amount of groundnut shell and sorghum husk are readily available to be used as potential material for adsorption instead of being disposed and causing environmental pollution.

Materials and Methods

Adsorption isotherms

Isotherms give an equilibrium relationship between the amounts of adsorbate adsorbed on the adsorbent surface and its concentration in the solution at a constant temperature. Numerous adsorption models are available in the literature to fit the experimental adsorption data. In this studys the data were fitted using Langmuir Freundlich and Temkin models. Each of the these models makes use of a parameter qe (i.e., adsorption capacity per unit mass of the adsorbent at equilibrium) in mg/g.

q_e=(C₀-C_e) V/X (1)

C₀=Initial concentration of solution (mg/l)

C_e=Equilibrium concentration of solution in (mg/l)

V=Volume of the solution used

X=Mass of the adsorbent used

Langmuir isotherm model

Langmuir isotherm model assumed monolayer adsorption (the adsorbed layer is one molecule in thickness) with adsorption can only occur finite (fixed) number of definite localized sides that are identical and equivalent with no lateral interaction and steric hindrances between the adsorbed molecule even on adjacent sites, in other words, sorption occur in a specific homogeneous site within the adsorbent site of the sorbents are identical and energetically equivalent. In its deviation, Langmuir isotherm refers to the homogeneous sorption which each molecules possess a contact enthalpies and sorption activation energy (all side possess the equal affinity for the adsorbate). With no transmission of adsorbed in place of surface. Graphically it is characterized by a place an equilibrium saturation point where one molecule occupies a site, no further adsorption can take place. The Langmuir isotherms is widely used and has found a successful application in many real sorption process. Moreover, Langmuir theory has related rapid decrease of the intermolecular attractive forces to the rise of distance [3].

The linear form of Langmuir expression:

Where

C_e is the equilibrium concentration of dye solution (mg/L),

q_e is the equilibrium capacity of dye on the adsorbent (mg/g),

q_o is the monolayer adsorption capacity of the adsorbent (mg/g),

b is the Langmuir adsorption constant (L/mg) and is related to the free energy of adsorption.

The essential characteristic of Langmuir isotherm is expressed in terms of dimentionless constant separation factor or equilibrium parameter RL, is define as:

RL=1/(1+bCo)

Where, Co is the initial adsorbate concentration (mg/g) and b is the Langmuir constant (L/mg). In the context, lower RL values reflect the adsorption is more favorable. In deeper explanation, R_L value indicate the adsorption nature is either unfavorable (R_L>1), Linear (R_L=1), favorable (01) or irreversible (R_L=0).

Freudnch isotherms

A Freunlich isotherm is a mathematical equilibrium between a fluid and a solid material. The Freunlich expression is a mathematical equation between an imperical expression representing the Isotherm variation of liquid or gas on a solid material. The slope ranges between 0 and 1 is a measure of adsorption intensity or surface heterogeneity, becoming more heterogeneous as its value gets closer to zero. Whereas, a value below unity implies chemisorption process where 1/n above one is an indicative of cooperative adsorption. It’s linearized and non-linear.

The linear form can be written as:

Where, kf and n (dimensionless constants) are the Freundlich adsorption isotherm constants, which indicate the capacity and intensity of the adsorption, respectively.

Temkin isotherm model

Temkin isotherm assumes that the adsorption heat of all molecules decreases linearly with the increase in the coverage on the surface of the adsorbent.

The general form of Temkin equation is giving below.

The linear form equation is written as:

The curve is obtain by plotting qe against ln C_e, with AT as Temkin isotherm equilibrium binding constant (L/g), bT Temkin isotherm constant R, is universal gas constant (8.314 j/mol K) and T, is temperature [4].

Groundnut shell

Groundnut botanically known as Arachis hypogeal belongs to Legumiminose family. A complete seed of groundnut is called the pod and the outer layer is called the shell. Brian George et al. investigate the groundnut shell fibers was found to be 38 mm and 0.2 mm diameter. Average tenacity of groundnut shell fiber is of 1.06 g/den. Also, average strain of the fibers was found to be 7.45 percent and average modulus 25.3 g/den (Figure 1) [5].

Figure 1: Groundnut shell.

Surghum husk

Sorghum husk is an agricultural waste from milling of guinea corn (Sorghum vulgare), guinea corn is an important food crop grown abundantly in northern part of Niger and Benue Rivers in Nigeria [6] (Figure 2).

Figure 2: Sorghum husk.

Chemical

Methylene blue dye chemical was used for the initial adsorption experiments. Other chemicals such as NaOH and HCl were used to keep the pH constant. The adsorbents used were groundnut shell and sorghum husk [7].

Apparatus:

• Graduated cylinder
• UV spectrophotometer
• Beaker
• Orbital shaker
• Separating funnel
• Sieve
• Distilled water
• PH meter
• Balance

Preparation of the adsorbent: Adsorbents (groundnut shell and sorghum husk) were collected from Sabon kauras Bauchi local government areas Bauchi state. The agricultural by product were washed and dried at low temperature (<105˚C) for 48 hours to remove moisture content. After the drying processs material were ground to fine powder and sieved through 600 μm size. The adsorbents is then used for the research work [8].

Procedure for adsorption isotherm studies: 50 ml of methylene blue solution of concentrations 10 mg/Ls 20 mg/Ls 30 mg/Ls 40 mg/L and 50 mg/L were prepared. 4.0 g of groundnut shell of the prepared sample was taken in to conical flasks containing the solutions with a known initial concentration and the solution was maintained at a constant pH and stirred until equilibrium concentration is reached. The equilibrium concentration is recorded and used for the Isotherm study. The same procedure was used to carry out the same experiment using 3.6 g of sorghum husk and methylene blue dye solution [9-11].

Results and Discussion

This section presents the results and discussions of the research (Table 1). The following data were used:

Volume of the solution used=50 ml

Mass of sorghum husk used=3.6 g

Mass of groundnut shell used=4.0 g

Table 1: Data obtained from adsorption of methylene blue on Surghum husk.

Methylene blue adsorption on Sorghum husk

The Langmuirs Freundlich and Temkin isotherm study for methylene adsorption on Sorghum husk was carried out. The Langmuirs Freunlich and Temkin plot were given in Figures 3-5 respectively.

The value of q_e is calculated using equation (1) and the values needed for the calculation of isotherms were recorded in table above.

Figure 3: Langmuir isotherm plot of MB on SH.

Figure 4: Freundlich isotherm of MB on SH.

Figure 5: Temkin isotherm of MB on SH.

From the Langmuirs Freunlich and Temkin isotherm plot of methylene blue removal on sorghum husks R² values of Langmuir constant was 0.99700 which is higher than R² value of Freundlich and Temkins this means that Langmuir data fitted well than Freundlich (0.983) and Temkin (0.9758) data in the adsorption process and that shows that the process is a monolayer adsorption process.

Methylene blue adsorption on groundnut shell

The Langmuirs Freundlich and Temkin isotherm for methylene blue adsorption on groundnuts shell was carried out. The Langmuirs Freundlich and Temkin plots are given in Figures 6-8 respectively.

The value of qe is calculated using equation (1) and the values needed for the calculation of isotherms were recorded in Table 2.

Table 2: Data obtained from adsorption of methylene blue on groundnut shell.

Figure 6: Langmuir isotherm of MB on GS.

Figure 7: Freunlich isotherm plot of MB on GS.

Figure 8: Temkin isotherm plot of MB on GS.

From the above Langmuirs Freunlich and Temkin isotherm plot of methylene blue removal on groundnut shells R² value of Freundlich constant is 0.960 which is higher than R² value of Freundlich and Tebkins this means that Langmuir data fitted well than Langmuir (0.9436) and Temkin (0.944) data in the adsorption process. That shows that the adsorption process is multilayer adsorption process (Table 3).

Table 3: Langmuir isotherm constant.

For Langmuir isotherm; a plot of Ce/qe was plot against Ce which indicate a homogeneous adsorption distribution of Langmuir isotherm. The values of b and Qo were obtained from the intercept and the slope of the graph (Table 4).

Table 4: Freundlich isotherm constant.

From the Freundlich constants (Table 5) the values of n are found to be greater than one (n>1) indicating that the adsorption is a physical process. The values of n ranges from 1-10 represent good adsorption process.

Table 5: Temkin isotherm constant.

The Temkin binding energy (b_T) is positive for all the experiments indicating that the process is endothermic.

Conclusion

For the adsorption of methylene blue on sorghum husks Langmuir isotherm is more suitable to fit the experiment data because it has R² value of 0.9710 value than the other models while for the adsorption of methylene blue on groundnut shells Congo red on sorghum husk and Congo red on groundnut shells Freundlich isotherm fitted well the experimental data due to high R² values of 0.960s 0.983 and 0.9720 respectively. The Temkin binding energy (b_T) are positive for all the experiments indicating that the process is endothermic.

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