Isothermal , Kinetic and Thermodynamic Studies of the Adsorption of Erythrosine Dye onto Activated Carbon from Periwinkle Shell

Isothermal, kinetic and thermodynamic studies of the adsorption of erythrosine dye onto activated carbon from Periwinkle shell was carried out. The Periwinkle shell were washed, dried, carbonized at 400C, crushed, sieved, chemically activated at 800C, cooled, washed and dried at 110C. Variable influencing factors, such as contact time, temperature and concentration were studied through singlefactor experiment, while other factors are kept constant (at 30min, 30C and 50mg/L) in each adsorption experiment. From the adsorption isotherms, the correlation coefficient for Redlich-Peterson is closer to unity than others used in the adsorption. The adsorption kinetic followed pseudosecond order reaction, while the thermodynamic parameters, (∆H) = 13.49KJ/mol, (∆S) = 43.48J/mol.K and (∆G) = 0.4, 0.06, -0.15, -0.27, -0.54, -7.30KJ/mol. These results obtained show that activated carbon from Periwinkle shell will be a good low-cost adsorbent for the removal of erythrosine from aqueous solution. Keywords— Adsorption, Erythrosine, Kinetic, Periwinkle shell, Thermodynamic.


I. INTRODUCTION
Discharge of colored wastewater from textile, paper, plastics, cosmetics and food industries in the waterways are the first detectable contaminants and in appearance create adverse conditions.Since most of the dyes are stable against light and heat and remain biologically indecomposable, it is difficult to remove them from the water.In some cases, decolorization of the industrial wastewater proved to be a major environmental issue [4].The coloration of the water by the dyes causes inhibitory effect on photosynthesis affecting aquatic ecosystems.The role of dyes in connection with variety of skin, lung and other respiratory disorder has been reported worldwide.The discharge of highly colored effluent into natural water bodies is not only aesthetically displeasing, but it also impedes light penetration, thus upsetting biological processes within a stream.In addition, many dyes are toxic to some organisms causing direct destruction of aquatic communities.Therefore, it is required to adopt appropriate methods for treatment of such wastewater before its discharge to the environment [5].In this study, the ability of Periwinkle shell carbon to remove erythrosine by adsorption is been studied.The adsorption capacity of the dye will also examined using the adsorption isotherm technique.The Langmuir, Freundlich and Redlich-Peterson isotherms will used to fit the equilibrium data.Pseudo-first order, pseudo-second order models, activation energy and thermodynamic equations will be used to fit the experimental data [3].

II. RESEARCH METHOD 2.1 Preparation of adsorbents
Sample of Periwinkle shells were picked from the environment in Elele, Rivers State, Nigeria.The Periwinkle shells were washed with tap several times to remove the dust and other water-soluble materials.The process continues until the washing water was colorless.They were respectively dried in the open air.The dried Periwinkle shell was carbonized in a furnace (SX-5-12) at 400˚C for 3 hours and the charred were allowed to cool to room temperature, ground and sieved (150 -600m).It was chemically activated by weighing 100gram of the ground carbonized charred in 300 ml of 0.1M HCl solution, thoroughly mixed and heated until it formed slurry.The slurry was transferred to a crucible and heated in a furnace (SX-5-12) at 800˚C for 3 hours and allowed to cool to room temperature and washed with de-ionized water, dried in an oven at 110˚C for 2 hours [1].

Preparation of adsorbate
The Erythrosine used is of laboratory grade (KEM LIGHT, India).The solution was prepared in de-ionized water from Ion-exchange (Indian) Ltd, Eleme, Port Harcourt, Nigeria.An accurately weighed quantity of the dye was dissolved in de-ionized water to prepare the standard solution.The adsorption amount of erythrosine dye adsorbed onto the Periwinkle shell adsorbent at equilibrium was calculated with the following equation:

International Journal of
Where C0 (mg/L) and Ce (mg/L) are the initial and equilibrium concentration of the dye, V (L) is the volume of solution, X (g) is the weight of adsorbent in one container.

III. THEORY 3.1 Adsorption isotherms
Adsorption isotherms of erythrosine were measured using concentration-variation method at constant temperature, time and volume [3].

Adsorption Isotherm Langmuir adsorption isotherm (model)
The model represents one of the first theoretical treatments of non-linear adsorption and suggests that uptake occurs on a homogenous surface by monolayer adsorption without interaction between adsorbed molecules.The rate change of concentration due to adsorption should be equal to the rate of concentration due to desorption.As a result, the Langmuir isotherm is as expressed in equation 3 Where Qo and b are Langmuir constants qe, is amount of solute removed or adsorbed at equilibrium.Ce, is equilibrium concentration of mixtures.Thus Qo, b and the squared of the regression coefficient (R 2 ), are adsorption parameters estimated by Langmuir model.It has been well documented that the essential characteristic of the Langmuir isotherm may be expressed in terms of the dimensionless parameter (RL) has been defined as isotherm shape that predicts if an adsorption system is favorable or unfavorable.RL is considered as a reliable indicator of the adsorption process.RL also indicates the assumption characteristics: The values of Log (qeqt) were linearly correlated with t.The plot of Log (qeqt) versus t should give a linear relationship from which K1 and qe can be determined from the slope and intercept of the plot, respectively.

Pseudo-second order equation
The pseudo-second-order adsorption kinetic rates equation is expressed as The plot of (t/qt) and t of equation 10 should give a linear relationship from which qe and K2 can be determined from the slope and intercept of the plot, respectively.

Kinetic parameters of activation
From the Van't Hoff equation, for isobaric and isochoric conditions, Arrhenius developed another equation called the rate constant K of a chemical reaction on the temperature.
For the adsorption process, upon integration and evaluation, the logarithm of the rate constant (K) could be represented as a straight line function of 1/T ln K = -

+ ln A 13
Where k is the rate constant, A is a frequency factor, R is the universal gas constant (8.314J.K -1 .mol - ) and T is the absolute temperature.The value of Ea is calculated from the slope of plotting lnk versus 1/T, and A (min -1 ) is determined from the intercept.
Equation 11 can also integrated within the limits T1 to T2 to give ln 1  2

14
Where KT2 = rate constant of chemical reaction at T2 KT1 = rate constant of chemical reaction at T1 [9].

Thermodynamic studies
The determination of the basic thermodynamic parameters: enthalpy of adsorption (ΔH), Gibb's free energy of adsorption (ΔG) and entropy of adsorption (ΔS), is important as these determines if the process is favorable or not from thermodynamic point of view, also to assess the spontaneity of the system and to ascertain the exothermic or endothermic nature of the process.An adsorption process is generally considered as physical if ΔH• < 84 kJ mol -1 and as chemical when ΔH• lies between 84 and 420 kJ mol -1 [11].
The thermodynamic parameters of the adsorption process were determined from the experimental data obtained at various temperatures using equations 15 to 17 where Kd is the distribution coefficient for the adsorption, qe is the amount of dye (mg) adsorbed on the adsorbent per L of solution at equilibrium, Ce is the equilibrium concentration (mg/L) of the dye in solution, T is the absolute temperature, R is gas constant, ∆  ,∆  , and ∆  are Gibbs free energy change, enthalpy change and entropychange, respectively.The values of enthalpy change (∆ o )and entropy change (∆ o ) are obtained from the slope and intercept of lnKd versus 1/T plots [1].The plots of t/qt versus t at 303, 313 and 323K all give straight line for the adsorption.The correlation coefficients for plots of t/qtagainst t for the second-order equation are observed tobe close to 1. Fig. 6 shows the dependency of the rate constant on temperature at 303, 313 and 323K, while values of the activation energy and frequency factor were obtained from the plot using eq (13).The parameters are presented in Table 2.

VI. CONCLUSION
The adsorption of erythrosine dye from aqueous solution onto Periwinkle shell was examined.The adsorption follows Redlich-Peterson isotherm, pseudo-second order kinetic, while the thermodynamic parameters show that the adsorption is physical and spontaneous.Considering the adsorption capacity and other parameters obtained, activated carbon from Periwinkle shell has good potential for the removal of erythrosine dye from wastewater.
the adsorption experiment are presented graphically in the figures below.
3.2 Adsorption kineticsThe pseudo first order and second order kinetic models need to be tested at different concentrations in this study to determine which model is in good agreement with International

Table .
Thermodynamic studiesThe plot of ln Kd versus 1/T is shown in Fig 5.The values of ∆H o and ∆S o of erythrosine dye adsorption was calculated using Eq. 17.The values of ∆G o were obtained by using Eq. 15.The thermodynamic parameters for the adsorption of Erythrosine dye is presented in

Table 3 .
Table.5: Enthalpy and Entropy change of some adsorbent for the dyes