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Research ArticleModified Cenospheres as an Adsorbent for the Removal ofDisperse Dyes

Markandeya Tiwari,1 S. P. Shukla,1 D. Mohan,2 D. S. Bhargava,3 and G. C. Kisku4

1Department of Civil Engineering, Institute of Engineering and Technology, Lucknow 226021, India2Department of Civil Engineering, Indian Institute of Technology (BHU), Varanasi 221005, India3Department of Environmental Engineering, IIT Roorkee and AIT, Bangkok, Bhargava Lane, Devpura, Haridwar 249401, India4Environmental Monitoring Division, CSIR-Indian Institute of Toxicology Research, M.G. Marg, Lucknow 226001, India

Correspondence should be addressed to G. C. Kisku; [email protected]

Received 23 December 2014; Revised 4 March 2015; Accepted 4 March 2015

Academic Editor: Jesus Simal-Gandara

Copyright © 2015 Markandeya Tiwari et al. This is an open access article distributed under the Creative Commons AttributionLicense, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properlycited.

The main objective of this investigation was to use modified cenospheres for the removal of disperse blue 79:1 (DB) and disperseorange 25 (DO) dyes from aqueous solution by batch adsorption process under different conditions (pH, adsorbent dose, adsorbateconcentration, agitation speed, contact time, and temperature). Modified cenosphere was capable of removing up to 78% of DBand 81% of DO dyes from aqueous solutions of 40mg/L dyes concentration. The investigated data was explained by the Langmuirisotherm. The experimental data were found to follow the pseudo-second-order kinetic model. The results of this study suggestedthat modified cenospheres could be used as a low-cost alternative to expensive adsorbents like activated carbon in wastewatertreatment for the removal of disperse dyes.

1. Introduction

According toConfederation of IndianTextile Industry, textilemills are discharging approximately 1.2 × 103 million litersper day (MLD) colored wastewater into the natural waterbodies without proper treatment [1]. There are 3441 textilemills in India out of which 3244 are spinningmills and 197 arecomposite mills. The annual consumption of synthetic andnatural fibers/filaments is 6800million kilos and 2601millionkilos, respectively. Total productions of Khadi (handloom)and others are 62625 million kilos. India’s export businessof textiles and clothing including of silk, jute, coir, andhandicrafts is about $300 billion (2013-2014) [1].

Presently, more than 1.0 × 105 commercially availabledyes are in the world whose production was >7.0 × 105 tonsannually [2, 3]. It has been anticipated that about 2% dyeis lost during manufacturing process while 10% is lost fromtextile and related industries [4, 5]. Among various dyes,disperse blue 79:1 (DB) and disperse orange 25 (DO) arecommonly used in textile industry in India [6].These are usedfor coloring of a wide range of synthetic as well as natural

fibers. Disperse dyes are preferred to acrylic blackO, redGTL,and others dyes due to its high tendency to bind the fibersand remaining persistent over the years. However, it becomestoxic in the water bodies because of its complex molecularstructure with fused aromatic groups [6].

Ions of disperse dyes in the water streams either reflectback the solar radiation or scatter in the water bodies.Solar radiation cannot penetrate beyond littoral zone andtherefore the deep water zone (i.e., aphotic zone) developsanaerobic condition. The entire ecological cycle includingself-purification system of water stream is disturbed due tolack of dissolved oxygen [7]. The indiscriminate dischargeof untreated wastewater is more conspicuous in case ofdeveloping countries rather than developed one, where theshortage of modern technology cum advanced knowledgeand insufficient funds are aggravating the problems [8].

The discharge of industrial effluents (textile mill, pulpand paper, tannery, distillery, carpet, and pharmaceuticalindustries) containing toxic components when entering thesurface water bodies causes severe environmental problemsas dyes damage the aesthetic nature of the environment.

Hindawi Publishing CorporationAdvances in Environmental ChemistryVolume 2015, Article ID 349254, 8 pageshttp://dx.doi.org/10.1155/2015/349254

2 Advances in Environmental Chemistry

N

N

N

N

N

N

NN

N

N

+

+ O

OO

O O

OO

O

O

O

O

O Cl

−

−

Figure 1: Chemical structures of DB (C23H25BrN6O10) and DO (C

17H17N5O2).

Most of the industries use dyes which are stable to lightand oxidizing in nature. Bacteria are partially effective incolor degradation as dyes are resistant to aerobic digestion[9]. According to various researchers, the elimination ofdyes from wastewater before their release into the naturalenvironment is an absolute necessity [10–12].

Coal fly ash (CFA) is a solid waste by-product of thecoal fired power plant which is not only encroaching onthe agricultural land but also creating environmental prob-lems. The lightweight portion of CFA is usually known ascenospheres; because they are hollow (empty sphere), theyform a large portion of the lightweight fraction. However,because they are collected in a sink through wet process, allparticles are less dense than water [13, 14]. There are severalreports which demonstrate the potential use of CFA for theremoval of organic synthetic dyes and toxic compounds fromaqueous solutions via surface-adsorption mechanism [15].Researchers studied adsorbent efficiency of coagulants (ferricchloride, ferrous sulfate, and alum) with CFA for the removalof dyes and pigments from the wastewater. The individualremoval efficiencies of ferric chloride, ferrous sulfate, alum,and CFA were 57%, 20%, 63%, and 58%, respectively; but theremoval capacity of hybrid processes of ferric chloride-CFA,ferrous sulfate-CFA and alum-CFA had markedly increasedand removed the pollutants up to 73%, 60%, and 68%,respectively [16].

Keeping in view, the toxicity and adverse environmentalimpact are likely to crop up due to discharged color wastes;the present study has been designed to develop suitablecheaper adsorbent material by modifying cenospheres toincrease the free surface binding sites and porosity of CFA.The main objective of this investigation is to determine thedye removal capacity of modified cenospheres from aqueoussolutions of disperse blue 79:1 and disperse orange 25.

2. Materials and Methods

2.1. Chemicals, Adsorbent, and Other Reagents. All thereagents used were of analytical grade (AR-grade). Dispersedyes (disperse blue 79:1 and disperse orange 25) with 99.9%purity were purchased from M/s Siddheshwari Industries,GIDC, Gujarat, India. Chemical structures and molecularformulae of DB andDOdyes are shown in Figure 1. Stock dyesolutions were prepared by dissolving 10 to 100mg of DB/DO

in 1 L double distilled water. The CFA was collected from thebottom of hopper of electrostatic precipitator installed at M/sPanki Thermal Power Station, Kanpur, Uttar Pradesh, India.

2.2. Preparation of Modified Cenospheres. Cenospheres weremodified to increase its adsorption capacity. First of all, ceno-spheres (low density CFA separated through wet method)were segregated and dried and finallymetals were leached outusing the toxicity characteristic leaching procedure (TCLP)method [17] to get modified cenospheres. Initially, extractionfluid was prepared by mixing 5.7mL glacial acetic acid firstwith 500mL reagent water and then with 64.3mL of 1NNaOH and finally volume was make up to 1 L by addingreagent water. 10.0 g of cenospheres was taken in flasks withextraction fluid in 1 : 20 w/v ratio. The mixture was thenshaken on orbital incubator shaker (G. G. Technologies, NewDelhi, Model: GGT 1201) at a speed of 30 rpm for 20 h atroom temperature. The leached metals will be dissolved insupernatant which is decanted and disposed of. The settledportion is dried at 100 ± 5∘C for 24 h in hot air oven (YorkScientific Industries, New Delhi, Model: YSI 431) and finallywe get modified cenospheres from CFA which has been usedas adsorbent in the present study.

2.3. Adsorption Studies. The batch experiments were per-formed to study the effects of pH, adsorbent dose, adsorbateconcentration, agitation speed, contact time, and tempera-ture. For this, 100mL of DB/DO dyes solution (concentrationvarying from 10 to 100mg/L) was taken in 250mL conicalflask having adsorbent dose varying from 0.1 to 01.0 g. ThepH (pH-meter Horiba Scientific, F74 BW) of mixture wasadjusted by adding 0.1 N NaOH and 0.1 N H

2SO4as per

requirements. The flasks were then subjected to agitation(speed varying from 80 to 240 rpm) using orbital incubatorshaker for proper adsorption. The contact time was variedfrom 5 to 300min. After adsorption, solution was separatedusing Whatman filter paper number 42 and residual concen-tration of dyes was measured spectroscopically at wavelengthof 545 nm for DB and 456 nm for DO using Dynamica UV-Vis single beam spectrophotometer (Model: Halo SB-10). Allexperiments were performed at three different temperatures(25∘C, 35∘C, and 45∘C) based on Indian climatic condition.

Advances in Environmental Chemistry 3

The percent removal of the dye was calculated using thefollowing equation:

Percent removal =(𝐶0− 𝐶𝑡) × 100

𝐶0

, (1)

where 𝐶0is the initial dye concentration (mg/L) and𝐶

𝑡is the

dye concentration (mg/L) after time 𝑡 (min).In order to optimize five parameters (such as pH, adsor-

bent dose, adsorbate concentration, agitation speed, andcontact time at three different temperatures), initially trialruns were conducted by fixing four parameters at a time andvarying fifth one.The optimum values of the parameters thusobtained from trial runswere used in final experimentswhereone parameter was varied and other four parameters werefixed.

2.4. Adsorption Isotherms and Kinetics. Adsorption capacityof adsorbent is defined as mass of dye adsorbed per unitmass of adsorbent and nature of the adsorption can bedescribed by relating the adsorption capacity to equilibriumconcentration of the solute remaining in the solution usingvarious isotherms [18]. The data obtained from batch exper-iments were tested for suitability of isotherms proposed byLangmuir [19], Freundlich [20], and Temkin and Pyzhev [21].The Langmuir isotherm assumes that the adsorption takesplace at specific homogeneous sites within the adsorbent.Thelogarithmic form of the Langmuir isotherm is expressed by

1

𝑞𝑒

=

1

𝑞𝑚

+ (

1

𝑏𝑞𝑚

)

1

𝐶𝑒

. (2)

The Freundlich isotherm is derived by assuming heteroge-neous surface with a nondistribution of heat of adsorptionover the surface. The logarithmic form of the Freundlichisotherm is expressed by

ln 𝑞𝑒= ln𝐾

𝑓+ (

1

𝑛

) × ln𝐶𝑒. (3)

Temkin and Pyzhev [21] suggested that the heat of adsorptionof all molecules in layer decreases linearly with coveragedue to adsorbent-adsorbate interactions and the adsorptionis characterized by a uniform distribution of the bondingenergies, up to maximum binding energy. The Temkinisotherm is represented by

𝑞𝑒= 𝐵𝑡ln𝐾𝑡+ 𝐵𝑡ln𝐶𝑒, (4)

where 𝐶𝑒is the concentration of adsorbate in solution at

equilibrium (mg/L), 𝑞𝑒is the amount of dye adsorbed on

adsorbent at equilibrium (mg/g), 𝑞𝑚is the maximum quan-

tity of dye required to forma singlemonolayer on unitmass ofadsorbent, 𝑏 is a parameter for apparent energy of adsorption,defined as 𝑏 = (𝑘

𝑎/𝑘𝑑), 𝑛 is the Freundlich exponent constant

that represents the parameter characterizing Quasi-Gaussianenergetic heterogeneity of the adsorption surface, 𝐾

𝑓is the

Freundlich constant indicative of the relative adsorptioncapacity of the adsorbents (L/g),𝐾

𝑡is the equilibriumbinding

455055606570758085

2 4 6 8 10 12 2 4 6 8 10 12 2 4 6 8 10 12

Dye

rem

oval

(%)

pH of mixture at different temperatures

DODB

25∘C 35∘C 45∘C

Figure 2: The effects of pH and temperature on % dye removal ofDB and DO.

constant (L/mg), and 𝐵𝑡is the variation of adsorption energy

(kJ/mol).The kinetics of adsorption of dyes on modified ceno-

spheres had been studied by the Lagergren pseudo-firstorder and pseudo-second order [22, 23]. The Lagergren rateequation is one of the widely used adsorption rate equationsfor the adsorption of solute from a liquid solution. Thepseudo-first-order kinetics of Lagergrenmay be expressed by

log (𝑞𝑒− 𝑞𝑡) = log 𝑞

𝑒− (

𝑘1

2.303

) × 𝑡. (5)

The pseudo-second-order kinetics of Lagergren is expressedin [12, 22, 24]

𝑡

𝑞𝑡

=

1

(𝑘2∗ 𝑞2

𝑒)

+ (

1

𝑞𝑒

) ∗ 𝑡, (6)

where 𝑞𝑡is the amount of dye adsorbed on adsorbent (mg/g)

at time 𝑡, 𝑘1is the rate constant of pseudo-first-order kinetics,

and 𝑘2is the rate constant of the pseudo-second-order

kinetics.

2.5. Statistical Analysis. Linear regression (SPSS 16) was con-sidered to understand the relationship between two variableson percent removal of DB and DO dyes. The rate of changein adsorption between two groups of dyes was calculated by𝛽 coefficient.

3. Results and Discussion

3.1. Batch Adsorption and Dye Removal. The results of batchadsorption and dyes removal are presented in Figures 2–6. The effects of five different parameters are as describedbelow. While varying one parameter, values of other fourparameters were kept constant as determined from trial runs(corresponding to maximum adsorption).

3.1.1. The Effect of pH. The effects of pH on adsorptionat various temperatures on dye removal are presented inFigure 2. In both dyes, the rate of removal (regression 𝛽 coef-ficient) was temperature dependent, decreases with increase


455055606570758085

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Dye

rem

oval

(%)

DODB

25∘C 35∘C 45∘C

Adsorbent dose at various temperatures (g/100mL)

Figure 3: The effects of adsorbent dose and temperatures on % dyeremoval of DB and DO.

455055606570758085

10 20 30 40 50 60 70 80 90 100 10 20 30 40 50 60 70 80 90 100 10 20 30 40 50 60 70 80 90 100

Dye

rem

oval

(%)

Adsorbate concentration at various temperatures (mg/L)

DODB

25∘C 35∘C 45∘C

Figure 4: The effect of adsorbate concentration and temperatureson % dye removal of DB and DO.

455055606570758085

80 100

120

140

160

180

200

220

240 80 100

120

140

160

180

200

220

240 80 100

120

140

160

180

200

220

240

Dye

rem

oval

(%)

Agitation speed at various temperatures (rpm)DODB

25∘C 35∘C 45∘C

Figure 5: The effect of agitation speed and temperatures on % dyeremoval of DB and DO.

455055606570758085

5 10 15 20 40 60 80 100

120

180

240

300 5 10 15 20 40 60 80 100

120

180

240

300 5 10 15 20 40 60 80 100

120

180

240

300

Contact time at various temperatures (min)DODB

25∘C 35∘C 45∘C

Dye

rem

oval

(%)

Figure 6: The effects of contact time and temperature on % dyeremoval of DB and DO.

in temperature, and is higher in DO as compared to DB. Atall temperatures, both dyes DO and DB showed maximumremoval at pH 6. Mohan et al. [25] also found maximumremoval of Rosaniline Hydrochloride dye onto fly ash at pH6. DO dye removal was 1.4, 1.1, and 1.0 times compared toDB at 25∘C, 35∘C, and 45∘C, respectively, when the pH wasvaried from 2 to 6. However, the net removal (i.e., % changefrom pH 2 to 6) of DO at 25∘C, 35∘C, and 45∘C was 15%, 14%,and 14%, respectively, whereas for DB, it was 13%, 13%, and13%, respectively. The net removal of DO was 2%, 1%, and 1%higher as compared to DB.

3.1.2. The Effect of Adsorbent Dose. At various temperatures,the effects of adsorbent dose on dye removal are presented inFigure 3. The removal of dyes increased with an increase ofadsorbent dose particularly from 0.1 to 0.3 g. The adsorbentdose and temperature showed similar trend of dye removal(regression 𝛽 coefficient) as in case of pH. The DO showedmaximum removal at 0.2 g while DB showed maximumremoval at 0.3 g at all temperatures. The regression analysisrevealed 2.0-, 1.6-, and 2.1-fold more removal in DO (from 0.1to 0.2 g) at 25∘C, 35∘C, and 45∘C, respectively, as comparedto DB (from 0.1 to 0.3 g). However, the net removal of DO(i.e., % change from 0.1 to 0.2 g) at 25∘C, 35∘C, and 45∘Cwas 23%, 19%, and 17%, respectively, and for DB (from 0.1 to0.3 g), it was 12%, 12%, and 8%, respectively. The net removalof DO was 11%, 7%, and 9%, respectively, higher than DB.The increase of dyes adsorption might be due to unbalancedattractive forces with the increase of surface area per unitmass of the adsorbent [26].

3.1.3. The Effect of Adsorbate Concentration. The effects ofadsorbate concentration at various temperatures on dyeremoval are summarized in Figure 4. Similar to effects of pHand adsorbent dose, in this case also, the rate of removal(regression 𝛽 coefficient) of DO is higher than DB anddecreases with increase in temperature for both dyes. Atall temperatures, both dyes DO and DB showed maximumremoval at 40mg/L of dye concentration. The regressionanalysis revealed that there is the same percentage removal ofDO and DB dyes at all three temperatures. However, the netremoval (i.e., % change from 10 to 40mg/L) of DO at 25∘C,35∘C, and 45∘C was 31.0%, 30.0%, and 28.6%, respectively,whereas for DB, it was 30%, 29%, and 28%, respectively.The net removal of DO was 1.0%, 1.0%, and 0.8% higher ascompared to DB. Observations of present study are similarto the findings of Doulati Ardejani et al. [27], in which theadsorption of Direct Red 80 dye from aqueous solution ontoalmond shells was maximum at 40mg/L.

3.1.4. The Effect of Agitation Speed. The effects of agitationspeed at various temperatures on dye removal are summa-rized in Figure 5.The contact time was kept as found in initialtrial runs. According to agitation speed and temperatures,the rate of removal (regression 𝛽 coefficient) of both dyesfollows similar trend as for pH, adsorbent dose, and adsorbateconcentration. At all temperatures, both the DO and DBshowed maximum removal at 140 rpm. The results are in


Table 1: Isotherms parameters for adsorption of DO and DB dyes on the modified cenospheres.

DyesLangmuir [19] Freundlich [20] Temkin and Pyzhev [21]

𝑞𝑚

𝑏

𝑅2 𝐾

𝑓𝑛 𝑅

2 𝐾𝑡

𝐵𝑡

𝑅2

mg/g L/mg L/g L/mg kJ/moleDO 33.33 0.12 0.99 4.82 1.96 0.94 7.07 1.28 0.98DB 32.26 0.03 0.99 1.28 1.39 0.98 6.09 2.55 0.89

accordance with the findings of Kisku et al. [12], in whichmaximum removal of DO andDB dyes on CFAwas observedat 140 rpm.The regression analysis revealed 1.3-, 1.0-, and 1.1-fold more removal of DO (from 80 to 140 rpm) at 25∘C, 35∘C,and 45∘C, respectively, as compared to DB. However, the netremoval (i.e., % change from 80 to 140 rpm) of DO at 25∘C,35∘C, and 45∘C was 30%, 23%, and 20%, respectively, andof DB, it was 24%, 22%, and 18%, respectively, and the netremoval of DO was 6%, 1%, and 2%, respectively, higher thanDB.

3.1.5. The Effect of Contact Time. The effects of contact timeat various temperatures on dye removal are presented inFigure 6. In both dyes, the rate of removal (regression 𝛽coefficient) was also temperature dependent and decreaseswith increase in temperature. However in case of DO, therate of dyes removal was more conspicuous than to DB.At all temperatures, maximum removal of DO and DB wasobserved at 100min and 120min respectively. Our findingsare in accordance with Namasivayam et al. [28], in whichmaximum removal of Congo red dye onto orange peel wasobserved between 90 to 120min. The regression analysisrevealed 1.2-, 1.1-, and 1.1-fold more removal (5 to 100min)in DO at 25∘C, 35∘C, and 45∘C, respectively, as comparedto DB. However, the net removal (i.e., % change from 5 to100min) of DO at 25∘C, 35∘C, and 45∘C was 27%, 27%, and26%, respectively, and for DB (5 to 120min), it was 23%, 22%,and 21%, respectively.The net removal of DOwas 4.0%, 5.0%,and 5.0%, respectively, higher as compared to DB.

It can be concluded that themaximum removal of DB dyeis obtained at pH 6, adsorbent dose 0.3 g/100mL, adsorbateconcentration 40mg/L, agitation speed 140 rpm, and con-tact time 120min. The optimum parameters for maximumremoval of DO dye are pH 6, adsorbent dose 0.2 g/100mL,adsorbate concentration 40mg/L, agitation speed 140 rpm,and contact time 100min. The experiments were concludedat three temperatures to observe the effect of temperatureon optimized parameters and maximum removal of dyes.The removal of dyes increased with increase in temperature.At 45∘C, maximum removal of dyes was observed whichapproximately is 10% higher than 25∘C temperature.

3.2. Adsorption Isotherms. For both DB and DO dyes, exper-imental isotherms were plotted using the data obtained fromthe batch experiments. Their constants and coefficient ofdetermination (𝑅2) are shown in Table 1.

The higher value of coefficient of determination (𝑅2 >0.98) close to 1 for Langmuir isotherm showed that bothdyes are more applicable and appropriate in describing the

data for modified cenospheres adsorbent. The adsorptionsites will be independent of the neighboring sites whichaccommodate only one dye molecule on each adsorptionsite in the form of complexes of reactive functional groupspresent on the surface of adsorbent. The calculated constantsof Langmuir, Freundlich, and Temkin isotherm for DO andDB dyes are shown in Table 1. Single layer adsorption of ionson modified cenospheres surface was reported by Langmuirisotherm. The low values in this study indicate a weak inter-action between adsorbate and adsorbent for ion-exchangemechanism [29]. The adsorption capacity of cenospheresadsorbent (33.33 forDOand 32.26 forDB) is comparablewiththose of commercial adsorbents such as biopolymer chitosan(12.70mg/g) [30], banana pith (20.29mg/g) [31], and wasteslurry (9.50mg/g) [32].

3.3. Adsorption Kinetics. The kinetics of adsorption has beenstudied to explain the dye uptake mechanism onto themodified cenospheres. It was observed that the adsorptionof dyes increases with increase of contact time. However, theadsorption of DB was quick in the first 120min and for DOwas 100min after which the rate of adsorption slowed downand stabilized as the equilibrium approaches. Adsorptionkinetics was studied using the Lagergren pseudo-first-ordermodel and pseudo-second-order model [12, 24, 33] and ispresented in Table 2 and Figure 7.

The mean values of kinetic rate coefficients 𝑘1(pseudo-

first-order kinetic model) are 0.034 ± 0.005 and 0.038 ± 0.004whereas 𝑘

2(pseudo-second-order kinetic model) are 0.020 ±

0.007 and 0.041 ± 0.009 for DO and DB dyes, respectively.The higher values of coefficient of determination (𝑅2 > 0.99)for pseudo-second-order kinetics show that both dyes aremore applicable and appropriate in describing the data. FromTable 2, it is concluded that removal of dye from modifiedcenospheres was well represented by pseudo-second-ordermodel for both dyes.

The scatter plots between experimentally observed (𝑞𝑒,exp)

and model calculated (𝑞𝑒,cal) values for pseudo-first and -

second order are shown in Figure 8.Based on slope/intercept and 𝑅2 values of trend lines,

we are getting the similar conclusion that removal of dyefrom modified cenospheres was well represented by pseudo-second-order model for both dyes.

4. Conclusions

It can be concluded that the optimumdetermined parameterswere pH 6, dye concentration was 40mg/L, and agitation


Table 2: Comparison of pseudo-first-order and pseudo-second-order kinetics at different concentrations of DO and DB dyes.

Dyes Pseudo-first-order kinetics Pseudo-second-order kineticsConc. DO DB DO DB(mg/L) 𝑞

𝑒,cal 𝑘1

𝑅2

𝑞𝑒,cal 𝑘

1𝑅2

𝑞𝑒,cal 𝑘

2𝑅2

𝑞𝑒,cal 𝑘

2𝑅2

10 1.03 0.04 0.91 2.70 0.03 0.93 4.74 0.03 0.99 2.36 0.05 0.9920 0.09 0.04 0.98 1.99 0.02 0.97 8.69 0.03 0.99 5.38 0.06 0.9930 0.07 0.03 0.98 1.98 0.02 0.97 12.82 0.02 0.99 8.07 0.04 0.9940 0.37 0.03 0.99 0.66 0.03 0.98 16.67 0.02 0.99 10.87 0.03 0.9950 0.56 0.03 0.96 1.69 0.03 0.97 20.00 0.02 0.99 11.91 0.05 0.9960 0.30 0.04 0.92 1.11 0.03 0.87 22.73 0.02 0.99 13.33 0.04 0.9970 0.20 0.03 0.94 1.55 0.03 0.90 25.00 0.01 0.99 14.29 0.04 0.9980 0.30 0.03 0.98 0.98 0.03 0.92 25.64 0.01 0.99 15.87 0.04 0.9990 0.21 0.04 0.91 0.91 0.03 0.84 27.78 0.02 0.99 17.54 0.03 0.99100 0.34 0.03 0.97 1.01 0.03 0.95 29.41 0.02 0.99 19.52 0.03 0.99𝑘1 and 𝑘2 are rate constants of pseudo-first-order and pseudo-second-order kinetics.

−3.0

−2.5

−2.0

−1.5

−1.0

−0.50 20 40 60 80 100 120

t (min)

log(q

e−

10 (mg/L)20 (mg/L)30 (mg/L)40 (mg/L)50 (mg/L)


qt)

(a) DB

−3.0

−2.5

−2.0

−1.5

−1.0

−0.50 20 40 60 80 100

t (min)

log(q

e−



qt)

(b) DO

0

500

1000

1500

2000

2500

3000

0 50 100 150 200 250 300 350t (min)

q1 (mg/g)q2 (mg/g)q3 (mg/g)q4 (mg/g)q5 (mg/g)


t/qt

(c) DB

0

200

400

600

800

1000

1200

1400

0 50 100 150 200 250 300 350t (min)



t/qt

(d) DO

Figure 7: Pseudo-first-order kinetics for (a) DB and (b) DO and pseudo-second-order kinetics for (c) DB and (d) DO dyes.


0

5

10

15

20

25

30

35

0 10 20 30

Pseudo-first orderPseudo-second order

y = −0.013x + 0.5909

R2 = 0.1449

y = 1.0277x + 0.0913

R2 = 0.9998

qe,exp

qe,cal

(a) DO dye

0

5

10

15

20

25

0 5 10 15 20

y = −0.1003x + 2.6185

R2 = 0.6679

y = 1.0396x − 0.1188

R2 = 0.9972

Pseudo-first orderPseudo-second order

qe,exp

qe,cal

(b) DB dye

Figure 8: Plot between experimentally observed (𝑞𝑒,exp) and model calculated (𝑞

𝑒,cal) values of pseudo-first-order and pseudo-second-orderkinetic model for (a) DO and (b) DB dyes.

speed was 140 rpm for both dyes while the adsorbent dosewas 0.3 g for DB and 0.2 g for DO. The equilibrium contacttime was 120min for DB and 100min for DO and the besttemperature was 45∘C. The maximum dyes removal capacityof modified cenospheres was found to be 78% for disperseblue 79:1 and 81% for disperse orange 25. The effect of pHrevealed thatmodified cenospheresmay produce good resultsat pH 6 that means it does not require any especial acidic orbasic chemical for dye removal.This pH 6 also falls within theprescribed limit of pH (5.5 to 9.0) of treated industrial effluentallowed to be discharged into the inland surface water bodiesin India. The adsorption process was explained by Langmuirisotherm having monolayer adsorption capacity 32.26mg/gand 33.33mg/g for DB and DO, respectively.The investigatedadsorptionmechanisms for disperse blue and disperse orangedyes followed the pseudo-second-order kinetics model. Ourresults suggest that modified cenospheres could be suitablyused as an alternative and effective resource materials ascompared to the expensive commercial adsorbents for theremoval of disperse blue 79:1 and disperse orange 25 fromcolored wastewater. The used modified cenospheres couldeasily be dumped into landfill with lining or in concretepits or can also be used in brick making to minimize theenvironmental risk.

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper.

Acknowledgments

The authors are grateful to Dr. K. C. Gupta, Director of CSIR-IITR, Lucknow, for providing necessary facilities for this

work. Special thanks are due toWorld Bank (TEQIP scheme),Uttar Pradesh, for providing necessary fund for this study.

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