Adsorption of Rhodamine-B Dye from an Aqueous Solution by Biomass Pine Apple Peel : Kinetics , Equilibrium and Thermodynamic Studies

Industrial wastewater is considered as one of the major pollutants of the environment [1]. Colored wastewater is produced by various industries, such as textile, dyeing, pharmaceutical, food, cosmetics and healthcare, paper and leather industries [2, 3]. Many dyes and their breakdown products may be toxic for living organisms. Therefore decolorization of dyes is important before the discharge of effluent. Removal of dye has been attempted extensively using physico-chemical methods such as coagulation, ultra-filtration, electro-chemical adsorption, photo oxidation, activated carbon adsorption, etc [5]. But these technologies are not efficient, satisfactory and also cost effective [4]. Adsorption has been shown to be one of the most promising and extensively used methods for the removal of both inorganic and organic pollutants from contaminated water [6, 7]. Use of low cost, easily available biomaterials for the adsorption of dyes is practiced as an alternative method and several botanical, low cost materials have directly been used as an adsorbent for removal of dyes from wastewater [8, 9]. Now days, agricultural waste materials are receiving much more attention as adsorbents for the removal of dyes from waste water due to its low cost and good availability. In the present study, pine apple peel (PAP) has been used as an adsorbent whose results showed good absorption in Rhodamine-B dye aqueous solution [10].


Introduction
Industrial wastewater is considered as one of the major pollutants of the environment [1].Colored wastewater is produced by various industries, such as textile, dyeing, pharmaceutical, food, cosmetics and healthcare, paper and leather industries [2,3].Many dyes and their breakdown products may be toxic for living organisms.Therefore decolorization of dyes is important before the discharge of effluent.Removal of dye has been attempted extensively using physico-chemical methods such as coagulation, ultra-filtration, electro-chemical adsorption, photo oxidation, activated carbon adsorption, etc [5].But these technologies are not efficient, satisfactory and also cost effective [4].Adsorption has been shown to be one of the most promising and extensively used methods for the removal of both inorganic and organic pollutants from contaminated water [6,7].Use of low cost, easily available biomaterials for the adsorption of dyes is practiced as an alternative method and several botanical, low cost materials have directly been used as an adsorbent for removal of dyes from wastewater [8,9].Now days, agricultural waste materials are receiving much more attention as adsorbents for the removal of dyes from waste water due to its low cost and good availability.In the present study, pine apple peel (PAP) has been used as an adsorbent whose results showed good absorption in Rhodamine-B dye aqueous solution [10].
The experiment was carried out by the batch adsorption method in the Erlenmeyer flasks for a predetermined period using orbital shaker.In the adsorption, parameters such as PH, Initial dye concentration, equilibrium time fixation were studied for optimization.The kinetic studies and isotherm study were carried out at different dye concentration 200ppm, 250ppm, 300ppm, 350ppm, 400ppm and 450ppm.By keeping temperature constant, at 150 rpm for 2 and half an hours.The mechanism of adsorption was investigated by Lagergren,s pseudo first order, pseudo-second order, Natarajan and Khalf first order, Bhattacharya and Venkobechar first order, Elvoich and Intra particle diffusion models.The isotherm study results were fitted in Langmuir, Freundlich, Temkin, Dubihin-Radushkevich isotherms.The thermodynamics study carried out at three different temperatures 310,320 and 330K.The measurement of absorbance of colour was done Spectrophotometrically.The equilibrium adsorption capacity was evaluated using the equation Where qe (mg/g) is the equilibrium adsorption capacity, Co and Ce is the initial and equilibrium concentrations (mg/L) of Rhodamine-B dye solution.V is the volume and m is the weight of adsorbent.

Results And Discussion
Effect of pH: Initial pH of dye can influence the adsorption of it on the surface.In the present study pH 1-10 was used to observe the better adsorption with initial concentration of dye 250ppm with 1 g/L PAP as adsorbent dosage.The reaction mixture was agitated for 1 hr at 310K with agitating speed ss150rpm.The most favorable adsorption was seen at basic pH 8, with 107.9 mg/g uptake of dye adsorption.It was shown in the Figure 1.
The surface of the adsorbent which may be negatively charged at higher pH,which favored for adsorption of the positively charged dye cations through electrostatic force of attraction.The adsorption of PAP to adsorbent consequently increased with an increase of pH values [11,12].So, optimum pH was 8.

Effect of biosorbent dosage
At optimum pH the biosorbent dose were increased from 0.5 g/L at intervals of 0.5g/L up to 5.5g.The reaction mixture was agitated for 1hr at 310K with agitating speed 150 rpm.The percentage of removal efficiency was found high at 4 g/L.So, optimum biosorbent dose was 4 g/L.It was shown in Figure 2.
Equilibrium time fixation:At optimum pH 8 and biosorbent dose 4 g/L the reaction mixture was agitated for 2 and half an hour with regular time intervals of 15 minutes at 310K.The maximum adsorption was found at 120 minutes.After that there is no increase in adsorption.It was shown in Figure 3.

Kinetic study of adsorption
The kinetics of Rhodamine-B adsorption by using PAP was studied at different time intervals and different initial concentration of dye.The kinetic parameters are helpful for the prediction of adsorption rate, give important information for designing and modeling the adsorption process [13].
The mechanism of kinetics was investigated by Natarajan and khalf first order, Elvoich model, Bhattacharya and Venkobechar first order, Lagergren , s pseudo first order, pseudo second order and intra particle diffusion models.The study was carried at different time intervals up to equilibrium time and at different ppm at 310K are shown in Table 1.
The linearized form of Natarajan and Khalf first order kinetics is presented as Where C 0 and C t are concentration of Rhodamine-B dye (mg/l) at time zero and time t respectively.K is first order adsorption rate constant (min -1 ) which was calculated from slope of the plot (log C 0 /C t ) against t which was given in Table 2 and Figure 4.The R 2 value from 0.849 to 0.866 (Table 5) and also does not fit for whole range of contact time so, it does not follow first order kinetics.

ELVOICH MODEL
The linearized form of Elvoich kinetic equation is presented as [14] q t = 1/β ln (α, β)] + log t/ β - ---------------------(4) Where α and β are constants calculated from Table 4 and from the intercepts and slopes plot q t against log t shown in Figure 6.The constant β is related to the extent of surface coverage.The simple Elvoich models used to describe second order kinetics, assuming of that the actual solid surface is energetically heterogeneous.The Elvoich model has R 2 =0.961 to 0.964 for adsorbents under study.Where α is initial adsorption rate 1 (mg/g /min) and β is related to the extent of the surface coverage and the activation energy for chemisorptions (g mg -1 ).The initial adsorption rate, decreased from -0.7885 to -0.7261 while increasing the initial dye concentration from 200 to 450.It was shown in Figure 6 and table 4 and 5.

Pseudo first order kinetics
The kinetic data were treated with the following Lagergren , s pseudo first order rate equation [15] for 250 ppm.Activation energy for chemisorptions (g mg -1 ).The initial adsorption rate decreased from -0.7855 to -0.7261, while increasing the initial dye concentration from 200 to 450 ppm.log (q e -q t ) = log qe-K 1 t/(2.303)-----------------(5) Where q t and q e are the amount adsorbed at time t and at equilibrium (mg/g) and K 1 is pseudo first order rate constant for the adsorption process (min -1 ).The plot of log (q e -q t ) versus t was shown.(Table 6 Figure 7)

Pseudo second order kinetics
The pseudo second order model can be represented in the following form [16,17] t/ q t = 1/ K2 q e 2 +1.t/ q e -- --------------------------------------(6) Where K 2 is the pseudo second order rate constant (g/ mg.min).The plots of t versus t/q t result was shown in Table 7 and Figure 9 for 250ppm.From the above results pseudo first order has R 2 value was 0.997 and pseudo second order kinetics has R 2 value was 1.0000.forfirst order q e experimental is 26.06 mg/g where as q e theoretical is 47.90 mg/g but for second order q e is experimental is 52.63 and q e theoretical is 47.90 mg/g .So for the second order only q e experimental and q e theoretical (mg/g) values are nearly same.From this, it clearly indicates that pseudo second order better fitted than pseudo first order.

Adsorption of Rhodamine-B Dye from an Aqueous Solution by Biomass Pine Apple Peel: Kinetics, Equilibrium and Thermodynamic Studies
Copyright: © 2016 Ramulu, et al.

Intra particle diffusion
According to Weber and Morris the intra particle diffusion constant (K i ) is given by the following equation [17] for 250ppm.----------------------(7) The intra particle diffusion would be the controlling step if this line passed through the origin .when the plots do not pass through the origin.This is indicative of some degree of boundary layers control and this further show that the intra particle diffusion is not the only rate controlling step but also other processes may control the rate of adsorption [18].K i (mg/g/min 1/2 ) values can be determined from Table 8 and from the Figure 9, slope of plot q t against t 1/2 .The R 2 value was 0.8865.

Adsorption isotherm
Equilibrium isotherm equations are used to describe the experimental adsorption data.The parameters obtained from the different models provide important information on the adsorption mechanism and the surface properties and affinities of the adsorbent.Linear regression is frequently used to determine the best fitting isotherm and the applicability of isotherm equation is compared by judging the correlation co-efficient.

Adsorption of Rhodamine-B Dye from an Aqueous Solution by Biomass Pine Apple Peel: Kinetics, Equilibrium and Thermodynamic Studies
Copyright: © 2016 Ramulu, et al.

Temkin isotherm
The Temkin isotherm is given as q e = βln A + βln C e

Adsorption of Rhodamine-B Dye from an Aqueous Solution by Biomass Pine Apple Peel: Kinetics, Equilibrium and Thermodynamic Studies
Copyright: © 2016 Ramulu, et al.Where A t (l/g) is the equilibrium binding constant corresponding to the maximum binding energy and constant B is related to heat of adsorption [25].A Linear plots of q e against ln C e .Enables the determination of constant B and A from slope and intercept (table 11 and Fig 12).The R 2 value is 0.994.

Conclusion
The aim of this paper was utilization of natural biosorbent PAP as adsorbent for the removal of Rhodamine-B dye.Even though Bhattarchaya and Venkobechar frist order kinectic model,lagergren , s pseudo first order kinetic model gave better results ,but pseudo second order kinetic model was best fitted kinetic of adsorption .The correlation co efficient R 2 = 1 for second order adsorption model and q e theoretical values are consistent with q e experimental value showed that pseudo

Adsorption of Rhodamine-B Dye from an Aqueous Solution by Biomass Pine Apple Peel: Kinetics, Equilibrium and Thermodynamic Studies
Copyright: © 2016 Ramulu, et al.   second order adsorption equation fit with whole range of contact time.Among isotherms, Freundlich isotherm was found to be best fitting model with respect to R 2 values.∆G, ∆H and ∆S values showed that favorable, spontaneous and endothermic.The PAP adsorbents have excellent adsorption capacity compare to any other non conventional adsorption.So PAP can be used as a low cost attractive alternative for costly activated carbon.

Figure 7 Figure 8 y
Figure 7