CODEN (USA): IJCRGG, ISSN: 0974-4290, ISSN(Online):2455-9555 Vol.10 No.12, pp 79-86, 2017
Abstract : Removal of Rhodamine-B from aqueous media was achieved onto carbonized powder of polyalthia longifolia seeds as a new low cost adsorbent. The adsorption of basic Rhodhamine-B occurred by studying the effect of adsorbent amount, dye concentration, contact time, pH and temperature. Adsorption Study of removal of Rhodhamine-B from aqueous solution at 610 nm wavelength has been investigated through a batch study. Solutions of dye having concentrations 10, 20, 30 & 40 mg/lit were used. Maximum removal of dye was found to be 93% for 10 mg/lit solution, in 120 min with 6.5 pH, 250 mg/50 ml as dose and 60°C temperature. The adsorption followed pseudo-2nd order kinetics. Both intra-particle and film diffusion governed the adsorption process. Thermodynamic parameters, such as standard Gibbs free energy (∆G0), standard enthalpy (∆H0) and standard entropy (∆S0) were calculated. All results found concluded that carbonized powder of polyalthia longifolia seeds could be effectively employed as effective new low cost adsorbent for the removal textile dyes from aqueous solutions. Keywords : Rhodhamine-B, Polyalthia Longifolia, Lagergren 1st order, Pseudo 2nd order, Kinetic and Thermodynamic, Clean & Cheap, Biosorbent.
Synthetic dyes are one of the most important hazardous species found in textile industry produces in wastewater. There are more than 100,000 commercially available dyes with over a tone of dye stuffs produced annually25. Dye houses, paper printers and textile dyers which uses dyes for different purposes, releases waste water in to nearby land or rivers without any treatment because the conventional treatment methods are not cost effective26. Its presence in water bodies reduces light penetration, precluding the photosynthesis of aqueous flora.
Numerous methods have been designed to remove dyes from waste water, and such methods can be divided into physical, chemical and biological methods. Among these, the adsorption technique using low cost adsorbents derived from various natural, agricultural and industrial wastes are effective in removing various dyes from waste waters. Adsorption is, however, more superior among all these methods because of its low cost, simple design, easy operation and the possibility of adsorbent recycling33. Various low cost adsorbents were prepared from waste agricultural materials such as coconut husk, date stone27, jujuba seed28, garlic peel29 ,
30 31 32
olive waste cake, apple wastes , periwinkle shelletc. The present study undertaken to evaluate the efficiency of a carbon adsorbent prepared from seeds of polyalthia longifolia for the removal of dye in aqueous solution.
To study the adsorption of dye all chemicals used were of analytical grade. Digital colorimeter (Make: Equiptronics) Model EQ-650-A and Digital pH Meter (Make: Equiptronics) Model EQ-610 were used.
1. Preparation of Carbonized Powder of Polyalthia Longifolia Seeds (CPPL)
Seeds of polyalthia Longifolia were collected from the local areas Hadapsar Pune district, India. The seeds were washed with water and dried at 110 to 120o C in the oven. Then they are crushed into small pieces then carbonized in the muffle furnace at temperature 600oC in presence of inert medium of nitrogen gas for 6-7 hrs. Carbonized material was grinded into fine powder with the help of mortar and pestle. Then it was passed through a 63 mesh sieve to get particles of uniform size and stored in air tight container.
2. Preparation of dye solutions
Rhodamine-B stock solution was prepared by dissolving 1000 mg of dye in 1 lit of distilled water, and lower concentrations were obtained by dilution of the stock solution. Rhodhamine-B solutions of different concentrations. (10 to 40 mg/L) were prepared by using the stock solution. The pH of solution adjusted using
0.1 N HCl or NaOH solutions.
3. Batch adsorption studies
Batch experiment was carried out with different concentrations of dye solutions from 10 mg/l to 40 mg/l taken in a 250 ml clean flask. 250 mg of adsorbent dose was mixed with Rhodamine B dye solution and kept on magnetic stirrer with heater. Experimental parameters such as, adsorbent dosage 250 mg, contact time is 120 min, pH-3 to 6.5, initial concentration 10 mg/l to 40 mg/l and temperature 25-60oC were investigated by changing one parameter at a time, while other parameters are kept constant. After filtration, the dye solutions were analyzed by using colorimeter. The percentage of Rhodamine B dye removal was calculated by using the following equation.
% Adsorption = (X / Co) * 100 Where, X = Amount adsorbed Co = Amount of Rhodhamine-B present in 50 ml Similarly adsorption capacity is calculated using equation. Adsorption capacity = ( X / m) * 1 Where, m = Amount of adsorbent in 50 ml dye solution
1. Effect of contact time
It is observed that initially the percentage removal of the dye increases rapidly and then increases in a slow and gradual manner till it reaches the equilibrium. This is because a large number of surface sites are available for adsorption at the initial stages and as the adsorption process continues the adsorption sites available decreases. There was no appreciable change in the adsorption percentage above 120 min. Hence all the experiments were conducted for a period of 120 min.
2. Effect of pH
Effect of pH on the adsorption capacity of adsorbent dose was studied in the pH range 3 to 6.5. The percentage of dye adsorption was determined by varying the pH of the solution, fixing the other parameters constant. The pH of the solution was adjusted by adding 0.1 N HCl or 0.1 N NaOH solution. When the pH increased and reached a maximum at pH 6 then pH of the medium was maintained at 6 for further studies.
3. Effect of Adsorbent dose
Effect of adsorbent dose on the removal of Rhodamine B dye from aqueous solution was investigated by varying adsorbent dose from 50 mg to 250 mg. keeping the other parameters constant. When the adsorbent dosage was increased the percentage of adsorption increased and reaches the maximum at an adsorbent dosage of 250 mg, further addition of the adsorbent dosage has no significant effect. The maximum dye uptake occurred at 250 mg dose, hence it was chosen as the optimized dose.
4. Effect of Initial concentrations and temperature
Effect of initial concentrations (10 to 40 mg/lit) and temperature (25 to 60oC) on adsorption were studied. During the experimentation work it was observed that as the concentration of Rhodhamine-B solution increases %removal decreases (51.56 to 86.05%) to (43.59 to 61.54%) at 25oC, while at 60oC it changes from
(65.12 to 93.02%) to (51.28 to 70.51%). As the concentration increases %adsorption decreases because less sites are available for adsorption, maximum dye uptake takes place at 250 mg/50 ml 10 mg/lit solution of Rhodhamine-B.
Lagergren Pseudo 1st Order Kinetic Model
The pseudo first order equation which was suggested by Lagergren is as:
Dq / dt = K1(qe – qt)
Where qe : Amount adsorbed at equilibrium (mg/gm) qt : Amount adsorbed at time t (mg/gm) K1 : Lagergren rate constant of pseudo 1st Order (min-1)
After integrating the equation between the limits
t =0 tot =tandq= 0 toq= qe
log (qe – qt) = log qe – K1 t / 2.3030 (1)
linear plot of log(qe-qt) vs. t are obtained and the lagergren rate constant, K1 are determined from the slope of plot.
Table 1: Lagergren Pseudo 1st Order Parameters
10 mg/lit | 20 mg/lit | 30 mg/lit | 40 mg/lit | |
---|---|---|---|---|
m | 0.001 | 0.001 | 0.001 | 0.001 |
c | -0.059 | 0.213 | 0.346 | 0.457 |
qe | -1.0423 | 1.633 | 2.2181 | 2.8641 |
K1 | 0.0023 | 0.0023 | 0.0023 | 0.0023 |
R2 | 0.677 | 0.677 | 0.80 | 0.644 |
Figure 1. Lagergren 1st Order
The plot of log(qe-qt) vs t indicates that they are not linear and the correlation coefficient, R2 Value is also very small. This clearly reveals that the pseudo first order model of Lagergren is not applicable to Rhodhamine-B and CPPL adsorption system.
Pseudo 2nd Order Kinetic Model
Pseudo 2nd order kinetic equation was developed by Ho and McKay which is given as:
dq /dt = k2 (qe – q)2
after integrating the equation between the limits t = 0 to t = t and q = 0 to q = qe gives
t/a=(1/k2qe2)+(1 /qe)* t (2)
Comparative value of m, c, qe and k2 for different concentration solution is as:
Table 2: Pseudo 2nd Order Kinetic parameters
10 mg/lit | 20 mg/lit | 30 mg/lit | 40 mg/lit | |
---|---|---|---|---|
m | 2.159 | 1.146 | 0.873 | 0.778 |
c | 18.14 | 9.771 | 7.157 | 3.784 |
qe | 0.4632 | 0.8726 | 1.1455 | 1.2853 |
k2 | 0.2569 | 0.1344 | 0.1064 | 0.1599 |
R2 | 0.99 | 0.99 | 0.99 | 0.99 |
Figure 2. Pseudo 2nd Order
After plot of t / q vs t it is observed that the nature of line is straight line which gives k2 and qe from the intercept and slope. So it follow pseudo 2nd order kinetic model.
Internal Diffusion Method (Weber and Moris)
The relation between amount adsorbed and the reaction time can be expressed as:
q=Kwt1/2 +C (3)
Where Kw: Intra paricle diffusion rate constant (mg/gm/min)
In this model, due to porous nature of adsorbent, pore diffusion is expanded to be surface sorption. Therefore the rate constant of intraparticle transport, Kw was evaluated from the slopes of linear portion of the plots of q Vs t1/2. The line is straight line but it does not passes through origin means it does not follow intraparticle diffusion
Figure 3. Internal Diffusion Method Table 3: Internal Diffusion parameters
10 mg/lit | 20 mg/lit | 30 mg/lit | 40 mg/lit | |
---|---|---|---|---|
c | 0.218 | 0.408 | 0.578 | 0.813 |
Kw | 0.021 | 0.041 | 0.049 | 0.043 |
Thermodynamic Parameters
Thermodynamic parameters, standard free energy (∆Go), change in Standard enthalpy (∆Ho) and change in Standard entropy (∆So) for the adsorption of Rhodamine B onto the adsorbent were calculated using the following equations. The negative value of ∆Go indicates that the adsorption process is spontaneous and highly favourable. The positive value of ∆So indicates the increased randomness at the solid solution interface. The positive value of ∆Ho indicates that the adsorption process is endothermic and physical in nature.
Thermodynamic parameters are evaluated using equation ∆G = -2.303 RT log Kc
Figure 4. Study of thermodynamic parameters Table 4: Thermodynamic Parameters for different concentration solutions of Rhodhamine-B solution
10 mg/lit | 20 mg/lit | 30 mg/lit | 40 mg/lit | |||
---|---|---|---|---|---|---|
25oC | Kc | 6.1666 | 4.1818 | 2.4736 | 1.6 | |
∆G | -4507.9 | -3545.4 | -2244.36 | -1164.68 | Spontaneous | |
30oC | Kc | 6.1666 | 5.3333 | 2.8823 | 1.6 | |
∆G | -4583.5 | -4217.7 | -2667.26 | -1184.22 | Spontaneous | |
40oC | Kc | 7.6 | 6.125 | 3.4 | 1.88 | |
∆G | -5278.7 | -4717.17 | -3185.18 | -1655.3 | Spontaneous | |
50oC | Kc | 13.33 | 7.14 | 3.7142 | 2.12 | |
∆G | -6957.2 | -5280.79 | -3524.41 | -2018.2 | Spontaneous | |
60oC | Kc | 13.33 | 7.14 | 4.07 | 2.39 | |
∆G | -7172.6 | -5444.29 | -3891.48 | -2414.18 | Spontaneous | |
∆H | 6596.19 | 2487.2 | 1272.3 | 643.3 | Endothermic behaviour | |
∆S | 356.51 | 181.7 | 97.7 | 54.12 | Favourable |
The equilibrium and thermodynamic studies related to the uptake of Rhodamine B dye by adsorbent from aqueous solution was studied. The adsorption was found to highly dependent on various parameters like adsorbent dosage, contact time, pH, initial concentration, and temperature. The adsorption data was fitted the best in Langmuir adsorption model. The result of this study indicates that this adsorbent can be successfully utilized for the removal on Rhodamine B from aqueous solution.
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