Selective removal and preconcentration of methylene blue from polluted water using cation exchange polymeric material

Author’s Accepted Manuscript Selective Removal and preconcentration of methylene blue from polluted water using cation exchange polymeric material Medhat Mohamed El-Moselhy, Soha. M. Kamal www.elsevier.com/locate/gsd

PII: DOI: Reference:

S2352-801X(17)30158-3 https://doi.org/10.1016/j.gsd.2017.10.001 GSD71

To appear in: Groundwater for Sustainable Development Received date: 1 July 2016 Revised date: 14 September 2017 Accepted date: 3 October 2017 Cite this article as: Medhat Mohamed El-Moselhy and Soha. M. Kamal, Selective Removal and preconcentration of methylene blue from polluted water using cation exchange polymeric material, Groundwater for Sustainable Development, https://doi.org/10.1016/j.gsd.2017.10.001 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Selective Removal and preconcentration of methylene blue from polluted water using cation exchange polymeric material Medhat Mohamed El-Moselhy and bSoha. M. Kamal

a

Chemistry Department, Faculty of Science, Al-Azhar university, Nasr city, Cairo, Egypt Chemistry Department, Polymer Research Laboratory, Beni-Suef University, 62514 Beni-Suef, Egypt b

E-mail: [email protected], phone: - 00201006292802 Abstract In this work, the selective adsorption and preconcentration of methylene blue dye from aqueous solution by using a strong acid cation exchanger (Purolite® SST60) was studied in a batch adsorption and column system. The removal of MB was found to be pH dependent and the highest adsorption capacity was observed at pH 8.5. The observed adsorption rate was relatively fast and the equilibrium was established within 30-60 min. The obtained adsorption data were treated with the different adsorption isotherms. The maximum adsorption capacities obtained from the Langmuir model was 113 mgg-1, 131 mgg-1, 155 mgg-1, 199 mgg-1, 262 mgg−1at 288, 293, 298, 303 and 308 K, respectively. Furthermore, the adsorption process was found to follow the pseudo-second-order kinetic model. The intraparticle diffusion study revealed that film diffusion might be involved in the present case. Thermodynamic parameters revealed the feasibility, spontaneity and endothermic nature of adsorption. The sorbents were successfully regenerated using 50:50 mixture of 2M HCl + 75 % methanol mixture solutions. Keywords: SST 60; Methylene blue adsorption; Equilibrium isotherm. Introduction Methylene blue considered as one of the most important heterocyclic organics that used in many different fields such as drugs and dyestuff industries. Colored compound can exist in different kind of pharmaceutical wastes with higher doses that could be considered to be more hazardous to public health due to its mutagenic and carcinogenic properties [1-6]. The colored organic wastes can be found in the effluents of different industries such as textile, plastic, dye, 1

dyestuffs, leather, cosmetics, pharmaceuticals, food, paper-making containing dyes and pigments, at different steps in the dyeing and finishing processes [7]. The thiazine cationic dye family such as Methylene blue (MB) (C16H18N3SCl) are commonly used for coloring industries for paper, temporary hair colorants [8-10], dyeing of cotton, wood, and silk. The hazardous effect of MB lies in the fact that; it can cause some kinds of harmful effects to humans. For instance, heart rate increase, shock, vomiting, jaundice, cyanosis, quadriplegia, and tissue necrosis[11-13]. Variety of removal techniques were applied for the removal of colored compound from polluted water such as adsorption [1-5, 14, 15], using membrane process, coagulation, flocculation, photodecomposition [16, 17], electrochemical oxidation[18], etc. Among these techniques, adsorption, has been proven to be the most potential one due to its flexibility, simplicity of design, high efficiency and ability to separate wide range of chemical compounds [1]. Until now, several adsorbents have been reported to be effective for dye treatment such as activated carbon [15, 19-22], chitosan [23], fly ash [22], clays[24], magnesium aluminate [12], etc. Recently, depending on the total cost, removal efficiency for large scale consumption, source abundance and engineering convenience, researcher attentions have been paid to low coast adsorbents including natural and synthetic ones such [25-27]. The use of ion exchanger is very common for the removal of inorganic waste. However, the use of polymers for the removal of organic wastes is not common. Polymeric materials contain various functional groups, which can provide active sites for dye binding. Furthermore, the existence of styrene-divinyl benzene matrix facilitate the binding of some dyes through the hydrophobic-hydrophobic interaction with aromatic rings. In most cases researchers based their works on the removal of organic compounds using advanced oxidation processes for the complete mineralization of the organic compound. However, recycling and ruse of organic pollutants is not common due to the processes are so complicated and needs more efforts to find the suitable adsorbent that could achieve it is mission. In this study, the use of SST60 strong acid cation exchanger beads as an adsorbent was tested for adsorption and preconcentration of MB from aqueous solution. The effects of contact time, pH, initial MB concentration and temperature on the adsorption were investigated. 2

Kinetics, isotherm studies and thermodynamic parameters calculations related to the process were also performed. 2. Experimental 2.1. Chemicals Methylene blue (MB) with the molecular formula (C16H18N3SCl) and 98% purity, Safranin C20H19ClN4, Rosaniline HCl (C20H19N3), methanol, NaOH

and hydrochloric acid were

purchased from Merck and were used as received without further purification. Purolite® SST60 (with characteristics depicted in Table 1) was purchased from the Purolite Company, USA 2.3. Adsorption experiments 1000 mg/L of MB stock solution was prepared by dissolving the equivalent amount of dye in DI water, which was then diluted to a variety of concentrations of 50, 100, 150, 200, 250, and 300 mg/L. 2.3.1. Batch adsorption experiments The investigation of MB adsorption using batch scale were carried out to understand the effect of varying the different experimental condition such as initial dye concentration, contact time, pH and temperature on the adsorption of MB on SST60 cation. During the experiments 0.1 gm of SST60 was added to 200 mL of MB dye solution, and the pH was adjusted by using 0.1 M NaOH or 0.1M HCl. The resulting reaction mixture was kept under constant stirring at 500 rpm. The dye concentration in reaction mixture was determined at characteristic wavelength of 664 nm, by double beam UV–visible spectrophotometer (Perkin-Elmer, Lambda 2). Then the amounts of MB adsorbed per unit mass of adsorbent (qe) were calculated from the differences between the initial and final MB concentrations in solution by the following equation: (

)

( )

3

where V is the volume of MB solution in L; Co and Ce are the initial and equilibrium concentrations in mg/L, respectively; and m is the mass of adsorbent in gram. 2.4. Adsorption kinetics In order to determine the adsorption kinetics of MB, the fit of the obtained experimental data was treated with pseudo-first-order, pseudo-second-order and intraparticle diffusion models. The pseudo-first-order rate model is defined as the following equation [24]: (

)

( )

where k (min-1) is the Lagergren rate constant of pseudo-first order, qt (mg/g) and qe (mg/g) are the amounts of MB adsorbed at time t (min) and at equilibrium. The values of k and qe were determined from the intercept and the slope of the plot of log (qe - qt) versus t. The pseudo-second-order rate model is as follows [24]: ( )

where k2 (min-1) is the rate constant of pseudo-second order. The plot of t/qt values vs t gives straight line relation with slope equal to qe and intercept equal to (1/k2qe2). The obtained value of K2 is used to calculate the initial adsorption rate constant h (mg g−1 min−1), at t→0 as follows (14): ( ) The existing MB molecules could be moved from the bulk of solution into the outer and inner solid phase of the polymeric material through an intraparticle diffusion. The possibility of intraparticle diffusion which is considered in most similar cases as the rate- limiting step of adsorption processes was explored by using the intraparticle diffusion model [25]: ( ) 4

From the graphical representation of the obtained results for qt vs t0.5 the values of constant C and kid (mol/g min0.5) can be determined from the intercept and slope respectively. 2.5. Adsorption isotherms The determination of different adsorption parameters was carried out by using Langmuir, Freundlich and Tempkin isotherm models. Some of the used isotherm are assuming the formation of monolayer of the adsorbate on the surface of the adsorbent such as Langmuir model. the linear transformation of the equation can be expressed as follows [20]: ( )

where qe and Qmax are dye equilibrium and maximum amount of MB onto the sorbent (mg/g) respectively. Ce is dye concentration at equilibrium in solution (mg/l). KL is Langmuir constant (L/mg) related to the affinity of binding sites and the free energy of sorption. When Ce/qe is plotted vs Ce a straight-line relation was obtained with slope and intercept equal to (1/Qmax) and 1/Qmax*KL) respectively. The empirical Freundlich equation for adsorption on a heterogeneous surface is commonly represented by [13]: ( )

Where KF and n are the Freundlich constants than can be determined from the intercept and slope of the plot of ln qe versus ln Ce. To evaluate the possible mutual interaction among the different species and the enthalpy of the adsorption Tempkin isotherm model can be used. The Tempkin isotherm equation in linear form is shown as [14] ( )

5

where R is gas universal constant (8.314 J.mol-1 K-1), T is the absolute temperature in Kelvin., bT (J.mol-1) is the Tempkin constant related to enthalpy of adsorption and aT (L.g-1) is equilibrium binding constant. The Tempkin constants bT and aT are calculated from the slope and intercept of qe versus ln Ce. 2.6. Adsorption thermodynamic The different thermodynamic parameters such as change in standard free energy enthalpy (

), and entropy (

) evaluated for MB adsorption onto SST 60 can be done

using the following equations [26]: ( )

The values of

and

(

)

(

)

were calculated from the slope and intercept of the plot of ln KD

versus 1/T. However, Standard Gibbs free energy change of sorption (

) was evaluated using

Eq. (10). 2. 7. Column Run Fixed-bed column runs for MB removal from synthetic, but representative, feed solutions were carried out using 11 mm-diameter glass columns, constant-flow pumps, and fraction collectors. The empty-bed contact time (EBCT) and superficial liquid-phase velocity (SLV) were recorded for each experimental column run. The water chemistry for all of the synthetic feed water was as follows: ’MB =100 mg/L; pH 8.5; other cationic dyes = 100 mg/L. The exhausted SST60 was regenerated using a mixed solution of 50:50 2M HCl and 78% CH3OH. After regeneration, the bed was rinsed with Na2CO3 to remove excess HCl and bring back the hybrid sorbent to working conditions for the next cycle of MB removal. Experimental setup for MB sorption was demonstrated in Figure 1. Column, fraction collector. 6

3. Results and discussion 3.1. Effect of initial concentration and contact time on MB adsorption Several parameters can affect the amount of adsorbed MB dye such as contact time. The effect of the contact time on the adsorption process is shown in Fig. 2. The data obtained revealed that the equilibrium was attained in a time range between 30 -50 min depending on the concentration of MB used. The data also indicate that more than 50 % was adsorbed within the displayed time range. Furthermore, the rate of adsorption process extremely fast during the initial period of adsorption, due to the easier access to the vacant adsorption sites, and then diminishes with time till attaining equilibrium which attributed to the consumption of adsorption sites offered by the polymeric SST60 material and the formation of monolayer. On the other hand, the change of MB concentration indicates that the adsorbed amount of MB at equilibrium increase with the increase of initial concentration due to the fact that as the initial concentration increase the mass transfer increases leading to higher adsorption obtained at equilibrium. 3.2. Effect of temperature on MB adsorption Since the rate of adsorption might be depend on the speed of MB particle diffusion and however, the raise of temperature causes the increase of ionic mobility for this reason the increase of temperature strongly affects the rate and amount of adsorbed species in most adsorption reactions. The data obtained for the effect of temperature (Fig. 3) on the rate and amount of adsorbed MB indicate that the elevation of adsorption temperature (288 - 308 K) markedly increase the adsorption. It is clear that the adsorption capacity increase from 113 to 262 mg/g with the increase in temperature from 288 to 308 K, which might indicate the endothermic nature of the adsorption process of MB onto SST 60. 3.3. Effect of solution pH on MB adsorption The effect of pH on the adsorption process using ion exchangers strongly affect the whole process since pH control the surface charge of both adsorbent and adsorbate. The data obtained 7

for the effect of pH on the adsorption of MB on SST60 is shown in Fig. 4. As illustrated in the Figure, varying the pH of solution strongly affects the amount of MB adsorbed. The MB uptake was found to be very low (12-24 mg/L) at lower pH (3.5-5.5) due to the fact that in acidic medium MB molecules interact with the hydrogen ions exist in solution giving rise to the formation of positively charged MB bulk species that could not compete with the hydrogen ions which is favorably adsorbed rather than MB. Upon raising up the pH, the amount of MB adsorbed increase gradually to reach maximum at pH range 8-9 which attributed to the fact that, at this pH range (8-9) the surface of MB is uncharged and hence can easily interact with the functional groups of the polymeric materials and replace the existing positive ions (H+ or Na+) and the selectivity will be switched toward MB. With further increase of pH to 10 the amount of MB adsorbed diminishes but still high if compared with the one in acidic medium. The explanation of this point may be due to MB can adsorbed under two different forces: - i) electrostatic interaction with functional groups of the cation exchanger (depends on the pH) ii) hydrophobic-hydrophobic interaction between aromatic rings of MB and polymeric matrix (independent on pH. 3.3. Adsorption kinetics In order to understand the adsorption kinetics, it is necessary to evaluate the kinetic mechanism of the adsorption process, for this reason the pseudo-first-order, pseudo-second-order and intraparticle diffusion models were applied to fit the experimental data. With respect to the pseudo-first-order model as described in Fig. 5 in which logarithmic values of log (qe-qt) were plotted against time. The values of k1 and qe were determined from the intercept and the slope respectively and tabulated in Table 2. On the other hand, the kinetic parameters (k2 and qe) of the pseudo-second order kinetics were calculated from the intercept and the slope of the plot of t/qt versus t. The intraparticle model constants were determined from the intercept and the slope of the plot of qt versus t (Fig. 7). Fig. 7 represents the plot of qt vs. t1/2 at different initial MB concentration. It is clear that the obtained relation is of multi-linear behavior, reflecting that the adsorption process could be 8

controlled by more than one process. Based on these plots, the sorption processes of MB are implicated by two different phases, beholding that the rate-limiting step is not governed by intraparticle diffusion. However, the initial period of the plot indicated an external mass transfer whereas the second linear portion is due to intraparticle or pore diffusion. 3.4. Adsorption isotherms The adsorption data recorded for the different doses of MB (Fig. 8) illustrate the linearized experimental data at different temperature for MB adsorption fitted with Langmuir model. The data obtained indicate that the maximum adsorption capacity at 308 K was found to be 262 mg MB/g SST60 as presented in table 1 compared to the other temperatures. The calculated value of Qmax is extremely high indicating the mutual affinity between MB and the used polymeric materials. On the other hands, the different adsorption parameters obtained at different temperature by fitting the collected data with Freundlich and Tempkin isotherm models were represented graphically in Figs 9-10 and the calculated parameters were tabulated in Table 3. It is clear that the highest value of R2 was obtained from Langmuir isotherm equation indicating that the adsorption was favorably fitted with Langmuir rather than the other isotherms. Furthermore, the calculated RL values are all greater than zero and less than unity indicating that the adsorption of MB is favorable at this working experimental conditions. 3.5. Adsorption thermodynamic The investigation of adsorption thermodynamics of organic compounds gave an idea about the adsorption behavior and how to predict the mechanism. As illustrated in Fig. 11 the values of and

were calculated from the slope and intercept of the plot of ln KD versus 1/T.

Standard Gibbs free energy change of sorption (

) was evaluated using Eq. (10). The

calculated thermodynamic parameters were tabulated in Table 4. As observed from Table 4 the calculated values of Gibbs free energy change (

) are negative however the values of

are

positive, indicating that the adsorption process is spontaneous and endothermic, respectively. Further the positive value of entropy change

, reflects randomness nature of process at the

solid/solution interface and the affinity of SST60 for MB adsorption. 9

3.4. Fixed bed Column Run Fixed-bed column run experiments were carried out to imitative service cycle conditions and to evaluate the removal capacity of MB on SST60. Fig. 12 provides MB effluent histories for three separate column runs under the same experimental conditions using SST60 cation exchanger. The column run results indicate that the capacity of polymeric materials lasts for more than 11000 bed volume before the break through of MB. During the column run the existing MB species replace the H+ attached to the functional groups of the polymeric materials till complete exhaustion. Furthermore, after consumption of all functional groups (-SO3-) the MB will diffuse into the polymeric material and adsorbed through the hydrophobic-hydrophobic interaction with the polymeric matrix that could give the adsorbent extra capacity to last for many bed volumes. 3.4.1. Effect of other cationic dyes on the adsorption of MB To investigate the selectivity of SST60 for the adsorption of MB two different cationic dyes have been added to the influent (Safranin and Rosaniline HCl). The data collected for the column run effluent histories was illustrated in Fig. 13. The data obtained indicate that the used cation dyes have no competing effect on the removal of MB. Furthermore, the cationic dyes indicate earlier breakthrough as soon as the column run was started.

This finding might indicate the strong

mutual affinity among SST60 and MB. 3.5. Regeneration and reuse of SST60 After fixed-bed column operation and complete exhaustion of SST60, the exhausted cation. Several trials have been carried out to determine the suitable solution for the process of complete regeneration of MB. Upon using of different concentration of HCl and C2H5OH, we found that the amount of regenerated MB did not exceed 30 % and 70 % for HCl and C2H5OH respectively of the total adsorbed amount of MB. This finding might indicate that the use of HCl can only regenerate the MB adsorbed on the active sites of polymeric materials due to Donnan membrane effect. However, the addition of ethanol facilitates the leaching of MB attached to the matrix of SST60. 10

Finally, the exchanger was regenerated using a 50% 2M HCl/ 50% methanol solution at lower pH ≤ 0.5. The regenerant effluent from two successive MB sorption– desorption cycles are shown in Fig. 14. In less than 100 BVs, approximately 100% of MB was desorbed from the SST60. Upon complete recovery of exhausted SST60 we can say that the polymeric material can be effectively reused for multiple cycles of sorption–desorption. During regeneration, there was no physical or chemical degradation of the spherical SSt60 beads. 3.6. Proposed Mechanism Based on the data obtained from the regeneration process, it is clear that the using of HCl only for the regeneration can displace the positively charged MB attached to the polymeric material functional groups. However, the using of ethanol only can leach the MB particles that attached to the hydrophobic parts of the polymeric materials. Furthermore, the regeneration with a mixture of HCl and ethanol can cause the complete regeneration of MB and recovery of the polymeric materials. Figure 15 is representing a simplified proposed mechanism scheme for the process of adsorption and regeneration. 4. Conclusion The present study shows that SST60 could be an eff ective adsorbent for removing MB cationic dyes from aqueous solution. The data obtained indicate the dependence of the process on initial pH and temperature of polluted water. The equilibrium data were fitted using the Langmuir, Freundlich, Tempkin isotherms and the former model provided a better mathematical fit. The maximum monolayer adsorption capacity obtained was 262 mg MB/g SST60 at 308 K. The adsorption process was feasible, endothermic and spontaneous with lower negative free energy ( G◦) values. The estimated enthalpy change ( H◦) and entropy change ( S◦) for the adsorption process were 25.88 kJ.mol-1 and 90.62 J. mol-1 K-1. The low value of adsorption process, while the positive value of

G◦ suggests a physical

S◦ reflects the affinity of SST60 for MB and

increased randomness at the solid-solution interface during adsorption. The exhausted polymeric materials were efficiently regenerated using 50:50 mixture of 2M HCl + 75 % methanol mixture solutions.

11

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Regenerate solution

Waste water Pump

13

Fraction sample collector

Figure 1. Schematic diagram of a setup for a fixed bed column run of cation exchange material and the regeneration process of the material.

120 50 mg 100 mg 150 mg 200 mg 300 mg

qe(mg MB/g R.)

100

80

60

40

20

0 0

10

20

30

40

time (min) Fig. 2. Effect of contact time on different concentration of MB adsorption

280 240

qe(mg MB/g R.)

200 160 120 80 40 0 285

290

295

300

305

310

o

T (K )

Fig. 3. Effect of Temperature on the amount of MB adsorbed

14

300

MB adsorbed

250 200 150 100 50 0 0

2

4

6

8

10

12

14

pH

Fig. 4. Effect of pH on the adsorption of 300 mg/L MB at 35 oC.

2.4

2.0

Log(qe-qt)

1.6

1.2

50 mg 100 mg 150 mg 200 mg 250 mg 300 mg

0.8

0.4

0.0 0

5

10

15

20

25

30

35

time (min)

Fig. 5. Pseudo-first-order model for the adsorption s of MB adsorbed by SST60

15

1.0

50 ppm 100 ppm 150 ppm 200ppm 250 ppm 300 ppm

0.8

t/qe

0.6

0.4

0.2

0.0 0

10

20

30

40

Time (min)

Fig. 6. Pseudo- second order model for the adsorption s of MB adsorbed by SST60

250

50 mg 100 mg 150 mg 200 mg 250 mg 300 mg

200

qe

150

100

50

0 2

3

4

5

t

6

7

0.5

Fig. 7. Intraparticle diffusion kinetics for the adsorption s of different concentration of MB by SST60

16

1.0 288 K 293 K 298 K 303 K 308 K

Ce/qe

0.8

Qmax (298K) = 261.78

0.6

0.4

0.2

0.0 0

20

40

60

80

100

120

Ce

Fig. 8. Linearized Langmuir adsorption model for the effect of temperature on MB adsorption. 5.4

288 K 293 K 298 K 303 K 308 K

5.2

Lnqe

5.0

4.8

4.6

4.4

2.8

3.2

3.6

4.0

4.4

Ln Ce

Fig. 9. Linearized Freundlich adsorption model for MB adsorption at different temperature.

17

288 K 293 K 298 K 303 K 303 K

0.20

qe

0.16

0.12

0.08 3.0

3.5

4.0

4.5

lnCe

Fig. 10. Linearized Tempkin adsorption model for the effect of temperature on MB adsorption.

0.8

Ln KD

0.6

0.4

0.2

0.0 0.00325

0.00330

0.00335

0.00340

0.00345

0.00350

1/T

Fig. 11. Van’t Hoff plot for the adsorption of MB on SST60

18

1.0 Influent Solution Ca2+= 40 ppm Mg2+= 20 ppm CO2= 120 ppm 3

0.8

SO2= 120 ppm 4

0.6

C/Co

SST60 Run I SST60 Run II SST60 Run III

pH= 8.5 EBCT = 1.5 SLV = 1.2

0.4

0.2

0.0 0

3000

6000

9000

12000

15000

Bedvolume

Fig. 12. Fixed Bed column run effluent history for the removal of MB

Influent Solution 2+ Ca = 40 ppm 2+ Mg = 20 ppm 2CO3 = 120 ppm 2SO4 = 120 ppm

1.0

0.8

0.6

SST60 Run I 100 mg/L Safranine 100 mg/L Rosaniline HCl

C/Co

pH= 8.5

0.4

0.2

0.0 0

3000

6000

9000

12000

15000

Bedvolume

Fig. 13. Fixed Bed column run effluent history for the removal of MB in the presence of other cationic dyes

19

300

Regenerated MB (mg/L)

250 200 150 100 50 0 0

20

40

60

80

100

Volume(HCl+C2H5OH)

Fig. 14. Regeneration of MB adsorption using 50:50 HCl/Ethanol mixture

20

MB SO

H+

MB SO3-

MB MB

3-

MB MB

MB

H+

MB

H

SO3-

SO3MB

H+

+

H

MB+ SO3-

+

MB MB

MB

H+

MB

SO3-

MB

SO3-

MB

3-

SO

SO3-

SO3-

SO3-

MB

SO3-

MB

MB+

SO3-

SO3-

SO3-

SO3-

50:50

MB+

SO3-

SO3-

MB

MB

+

SO

SO

SO3-

SO3- H+

MB

MB SO3MB

MB

MB+

MB

SO3- MB+

MB

MB

+ SO3- MB

SO3MB+

SO

+

MB

SO3-

MB SO3-

MB

MB+

SO SO3-

H+

3-

MB

MB

3-

MB

3-

SO3-

MB

MB

SO3SO3-

SO3-

MB

H+

MB

MB+ SO3-

SO3-

MB+

MB+

H

MB

MB+

MB

MB+

+ SO3- MB

SO3-

MB+

3-

SO

SO3-

MB

MB

+

MB

3-

MB+

SO3-

SO3-

MB

SO3-

MB

MB

MB SO3-

SO3-

MB+ MB

MB

H

MB

SO3- H+

MB

SO3-

MB

MB

H+

MB

MB+

SO3-

HCl/Ethanol

SO3-

SO3-

MB MB+

MB

+

MB

MB+

SO3MB

MB MB

SO3-

MB SO3-

SO3-

MB

MB+

SO3-

+

MB

H+ SO3-

H+ SO3-

SO3H

MB

MB MB

MB+

SO3-

MB

MB

SO3-

MB

MB

MB

MB MB

SO3-

H+

MB H+

H

+

MB

SO3-

HCl

SO3-

MB

SO3- MB+

SO3-

SO3MB+

MB+

MB

SO3MB

SO3-

MB+

MB+

SO3-

MB+

+

SO3SO3-

Ethanol

MB+ SO3SO3-

MB+ SO3-

MB+ SO3-

MB+

MB+ 3-

SO SO3MB+

SO3-

SO3- MB+

MB+ 3-

SO SO3MB+

Fig. 15. Proposed mechanism for the MB adsorption and regeneration

MB+

Polystyrene crosslinked with Divinylbenzene Clear Spherical beads 90% min. Polystyrene sulphonate Na+ 33 - 45 > 1500 gm/bead (chatillon) 50 lb/ft3 +1.2 mm < 5%, -0.3 mm < 1% 0 - 14 1.20

21

+ SO3- MB

SO3-

Table 1: Typical physical and chemical characteristics of SST60 Polymer Matrix Structure Physical Form and Appearance Whole Bead Count Functional Groups Functional Groups Ionic Form, as shipped % Moisture Crush Strength Shipping weight (approx.) Particle Size pH Limits Specific Gravity, Na+ Form

MB+

3-

SO

MB+

Table 2: Kinetic parameters obtained from Lagrangian models in the adsorption of MB using SST60 Co

Pseudo first order

Pseudo second order

k1(min-1)

qe(mgg-1)

R2

k2(min-1)

qe(mgg-1)

h(mgg-1 min-1)

R2

50

0.11

79.4

0.97

0.0031

51.0

8.1

0.998

100

0.092

102.3

0.99

0.0016

66.7

7.12

0.997

150

0.089

133.1

0.95

0.0011

81.97

7.39

0.999

200

0.083

181.8

0.98

0.0005

161.29

6.61

0.999

300

0.087

263.0

0.95

0.0001

239.8

5.7

0.999

Table 3: Calculated Adsorption isotherms of MB using SST60 at different Temperature

Temperature

Langmuir model

Freundlich model

qmax

KL

RL

R2

288

113

0.042

0.073

293

131

0.055

298

155

303 308

Tempkin model

n

KF

qmax

R2

aT

bT

R2

0.999

5.6

45.6

102.6

0.981

14.6

0.6

0.987

0.038

0.997

4.55

42.95

116.7

0.981

10.9

0.35

0.99

0.071

0.044

0.998

4.0

43.82

135.4

0.985

8.75

0.22

0.99

199

0.086

0.037

0.999

3.0

39.65

166.7

0.96

5.9

0.13

0.99

262

0.110

0.029

0.999

2.56

36.6

206.6

0.92

4.3

0.061

0.99

22

Table 4: Calculated thermodynamic parameters for the effect of Temperature on the Adsorption of MB using SST60 Thermodynamic parameters Temperature

KD

Ln KD

288

1.098901

0.094311

-0.22582

293

1.328021

0.28369

-0.69107

298

1.552795

0.440057

-1.09027

303

1.876173

0.629234

-1.58513

308

2.222222

0.798508

-2.04475

Go (KJ mol-1)

H* (KJ mol-1)

S* (J.K-1.mol-1)

R2

25.88

90.62

0.997

Highlights -

Removal and regeneration of methylene blue dye from polluted water was studied.

-

The removal of methylene blue was found to be temperature and pH dependent. The adsorption process was found to follow the pseudo-second-order kinetic model. Thermodynamic parameters showed the feasibility and endothermic nature of adsorption. The sorbents were successfully regenerated using HCl/Methanol mixture solutions.

-

-

23