Application of activated carbon derived from scrap tires for adsorption of Rhodamine B
Journal of Environmental Sciences 2010,22(8)1273–1280
Application of activated carbon derived from scrap tires for adsorption
of Rhodamine B
Li Li 1,Shuangxi Liu 1,?,Tan Zhu 2
1.Institute of New Catalytic Materials Science,College of Chemistry,Nankai University,Tianjin 300071,China.E-mail:lillyfeng@https://www.sodocs.net/doc/3214563393.html,
2.College of Environmental Science and Engineering,Nankai University,Tianjin 300071,China
Received 09October 2009;revised 05January 2010;accepted 08January 2010
Abstract
Activated carbon derived from solid hazardous waste scrap tires was evaluated as a potential adsorbent for cationic dye removal.The adsorption process with respect to operating parameters was investigated to evaluate the adsorption characteristics of the activated pyrolytic tire char (APTC)for Rhodamine B (RhB).Systematic research including equilibrium,kinetics and thermodynamic studies was performed.The results showed that APTC was a potential adsorbent for RhB with a higher adsorption capacity than most adsorbents.Solution pH and temperature exert signi?cant in?uence while ionic strength showed little e ?ect on the adsorption process.The adsorption equilibrium data obey Langmuir isotherm and the kinetic data were well described by the pseudo second-order kinetic model.The adsorption process followed intra-particle di ?usion model with more than one process a ?ecting the adsorption process.Thermodynamic study con?rmed that the adsorption was a physisorption process with spontaneous,endothermic and random characteristics.
Key words :activated pyrolytic tire char;Rhodamine B;adsorption isotherm;thermodynamics DOI :10.1016/S1001-0742(09)60250-3
Introduction
Hazards associated with scrap tires can cause both health and environmental problems (Jang et al.,1998).The accumulation of scrap tires results in large spaces occupied and a wastage of a valuable energy resource.The huge amount and high stability of scrap tires have made their disposal a serious environmental problem.Although pyrolysis is considered as an e ?ective and environmental friendly disposal method,a proper utilization for the residues generated is still a problem to be solved (de Marco Rodriguez et al.,2001).Pyrolytic tire char accounts for 30%–40%of the original tire mass,and its utilization signi?cantly determines the pro?tability of the tire pyrol-ysis process at industrial scale (Kaminsky and Mennerich,2001;Ko et al.,2004;Piskorz et al.,1999).However,the complexity and the presence of contaminants such as ash,sulfur containing byproducts and oily condensates,have restricted the direct application of the pyrolytic tire char.One potential application for the pyrolytic tire char is to produce activated carbon (Cunli ?e and Williams,1998;Ko et al.,2004;Li et al.,2005;Mui et al.,2004;Teng et al.,2000;Zabaniotou and Stavropoulos,2003).These tire-derived activated carbons have been applied for the adsorption of e ?uent pollutants such as phenols (Helleur et al.,2001;Nakagawa et al.,2004;San Miguel et al.,
*Corresponding author.E-mail:sxliu@https://www.sodocs.net/doc/3214563393.html,
2002;Tanthapanichakoon et al.,2005),heavy metal ions (Hamadi et al.,2001),pesticides (Hamadi et al.,2004),and dyes (Garcia et al.,2007;Nakagawa et al.,2004;San Miguel et al.,2002;Tanthapanichakoon et al.,2005).Their application in gaseous phase has also been studied and was found to be feasible for the removal of acetone,trichlorethane,mercury chloride,and mercury (Lehmann et al.,1998;Manch′o n-Vizuete et al.,2005;Seneviratne et al.,2007;Skodras et al.,2007).
However,in previous works,the pyrolytic tire char studied in pollution control is limited to laboratory or pilot scale (Garcia et al.,2007;Hamadi et al.,2001,2004;Helleur et al.,2001;Lehmann et al.,1998;Manch′o n-Vizuete et al.,2005;Nakagawa et al.,2004;San Miguel et al.,2002;Seneviratne et al.,2007;Skodras et al.,2007;Tanthapanichakoon et al.,2005),and no research work has been done on pyrolytic tire char in industrial scale.
Highly colored wastewater containing hazardous dyes is another serious environmental problem.The high organic concentration,toxicity,complex composition and poor degradability of dye-containing wastewater have impeded the development of e ?cient puri?cation and treatment methods.At present,the studies of dye removal by pyrolyt-ic tire char (Garcia et al.,2007;Nakagawa et al.,2004;San Miguel et al.,2002;Tanthapanichakoon et al.,2005)were mainly limited in Methylene Blue.Moreover,only adsorp-tion capacity was examined,whereas adsorption kinetics,
1274Li Li et al.V ol.22
thermodynamics and e ?ect of operating parameters on the adsorption process have not been studied.These properties are vital in supplying the basic information required for the design and operation of adsorption process.In addition,the di ?erence in the nature of adsorbates could make the adsorption process di ?erent.Therefore,it is necessary to study the adsorption phenomena of other class of dyes.Rhodamine B (RhB)is a highly water soluble,basic red dye of the xanthene class.It is a typical cationic dye that has been widely used as a colorant in textiles and food stu ?s.It is also a well-known water tracer ?uorescent and biological stains.
It would be a promising and e ?ective way to treat the wastewater by the activated carbon derived from scrap tires.The present study aims to assess the applicability of activated carbon derived from the industrial-scale pyrolytic tire char for the adsorptive removal of RhB from aqueous solution and to investigate the kinetics and mechanism of the adsorption process.The system variables studied include initial dye concentration,adsorbent dosage,tem-perature,initial solution pH and ionic strength.
1Materials and methods
1.1Materials
Pyrolytic tire char was obtained from an industrial pyrolysis plant with annual processing capacity of 10,000tons of scrap tires in Shanghai Greenman ECO Science and Technology Co.,Ltd.,China.Activated pyrolytic tire char (APTC)was prepared according to our previous patent
(Liu et al.,2008).Brie?y,pyrolytic tire char was treated ?rst by toluene to remove the rudimental pyrolysis oil and subsequently by dilute acid to remove inorganic ashes.Af-ter that,steam activation was performed at 800°C for 3hr.The structure characteristics of APTC were investigated by N 2adsorption-desorption on Tristar 3000(Micromeritics,America).The value of the pH required to give zero net surface charge,point of zero charge (pH pzc )of APTC was determined by the pH drift test (Rivera-Utrilla et al.,2001).RhB (C 28H 31N 2O 3Cl;maximum absorption wavelength 556nm),analytical grade,was purchased from Yingdax-igui Chemical Ind.Ltd.(Tianjin,China).Its chemical structure is shown in Fig.1.Absorbance measurements were carried out on a 2550UV-Visible spectrophotometer (Schimadzu,Japan).1.2Adsorption studies
Batch experiments were performed to investigate the adsorption process of RhB by the APTC.For each experimental run,100mL of RhB solution of known concentration,initial pH,ionic strength and the amount of the APTC were taken in a 250-mL stoppered conical ?ask.This mixture was agitated in a temperature-controlled shaking water bath at a constant speed of 200r /min and certain temperatures.
For adsorption equilibrium studies,RhB solutions of di ?erent concentrations (20–150mg /L)were contacted with a certain amount of APTC under certain conditions for 12hr insuring the equilibrium was achieved.The residual RhB concentration was then measured and the amount of RhB adsorbed onto APTC was
calculated
Fig.1Chemical structure of RhB.(a)cationic form;(b)zwitterionic form;(c)three dimensional structure.
No.8Application of activated carbon derived from scrap tires for adsorption of Rhodamine B1275 from mass balance.E?ects of contact time,adsorbent
dosage,initial RhB concentration,initial solution pH,ionic strength and temperature)on RhB adsorption by APTC were investigated.
Adsorption kinetics was determined by analyzing ad-sorptive uptake of RhB from aqueous solution at di?erent time intervals.The amount of RhB adsorbed at time t,q t (mg/g),was calculated using mass balance equation.
2Results and discussion
2.1Characterization of APTC
The structure parameters evaluated from N2adsorption-desorption analysis and physicochemical characteristics of APTC are listed in Table1,and compared with other forms of activated carbon from literature.It can be seen that APTC has similar BET surface area with other forms of activated carbon.The porosity of APTC is well developed with higher percentage of mesopore structure and larger average pore size,which are advantageous for dye adsorp-tion.As indicated in Table1,the pH pzc of APTC is about 6.7,thus,the surface charge of APTC is positive when solution pH is lower than6.7,and vice versa.
Table1Physicochemical characteristics of activated pyrolytic tire char (APTC)and other activated carbon from literature Parameter Adsorbent
APTC Sago waste BPH
activated activated
carbon a carbon b BET surface area(m2/g)720625523 Total pore volume(cm3/g) 1.050.670.39 Mesopore volume(cm3/g)0.92–0.30 Average pore diameter D BJH(nm)8.7– 3.0 Point of zero charge,pH pzc 6.7 5.7 3.9
a Kadirvelu et al.,2005;
b Gad and El-Sayed,2009.
2.2Adsorption capacity
Herein,the e?ect of operation parameters on the ad-sorption capacity of APTC for RhB was investigated.In addition,the observed adsorption equilibrium data were ?tted by the Langmuir and Freundlich isotherms.
2.2.1E?ect of operation parameters on adsorption ca-
pacity
The e?ect of temperature on the adsorption capacity of APTC is shown in Fig.2.It can be seen that the adsorption capacity is almost independent of temperature but signif-icantly positively dependent on initial RhB concentration at lower initial concentrations(20–50mg/L).However, when initial RhB concentration is higher than50mg/L, an increase of temperature enhances APTC’s adsorption capacity,while the increase of RhB concentration has little impact on APTC’s adsorption capacity.The main reason is that at the lower concentrations,the APTC could adsorb almost all of RhB.According to the mass balance equa-tion,the APTC adsorption capacity positively increases with initial RhB concentration,while temperature has
no Fig.2E?ect of temperature on the adsorption capacity of APTC. Conditions:natural pH;NaCl concentration0;adsorbent dosage0.2g/L. signi?cant in?uence under this condition.As for RhB concentrations higher than50mg/L,the APTC is satu-rated.Therefore,the increase of initial concentration has no in?uence on adsorption capacity while the temperature could a?ect the adsorption capacity.The enhancement of adsorption capacity of APTC at higher temperatures can be attributed to the following reason.The thermal motion of RhB molecules becomes more frequent at higher temperatures,which is favorable for more RhB molecules to be adsorbed by the same amount of APTC.
The solution pH plays an important role in the whole adsorption process and particularly on the adsorption capacity.The e?ect of initial solution pH on APTC ad-sorption capacity for RhB is presented in Fig.3.The maximum removal(around100%)for RhB was found at pH4.0.The removal decreased to about80%at highly acidic condition(pH3.0)and reached minimum(about 75%)at pH7.0.However,when the pH of the solution was further increased(>7.0),the uptake of RhB increased to over97%.Therefore,both acidic and basic solutions are suitable for RhB removal.
RhB is an aromatic amino acid with amphoteric char-acteristics due to the presence of both the amino
group Fig.3E?ect of initial solution pH on the adsorption capacity of APTC.Conditions:temperature25°C;initial RhB concentration50 mg/L;adsorbent dosage0.2g/L;NaCl concentration0.
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(–NHR 2)and the carboxyl group (–COOH).Thus,the charge state of RhB is dependent on solution pH.The p K a value for the aromatic carboxyl group presented on the RhB molecule is about 4.0.When the solution pH is lower than 4.0,the RhB ion takes on a positive charge on one of the nitrogens while the carboxyl group is unionized (Fig.1a).The electrostatic repulsion between cationic RhB and positively charged APTC leads to the decreased percentage of adsorption when pH decreased from 4.0to 3.0.When solution pH increased above 4.0,the carboxyl group gets ionized and the zwitterions form of RhB (Fig.1b)is formed (Deshpande and Kumar,2002).The zwitterion form of RhB in water may increase dimerization of RhB,which makes the molecule too large to enter most of the pore structure of APTC.The inaccessibility to the pore structure of APTC,which is smaller than the dimer’s e ?ective size,resulted in a decrease in RhB removal.The greater aggregation of the zwitterionic form is due to the electrostatic attraction between the carboxyl and xanthane groups of the monomer.When the pH is higher than 7.0,excessive OH ?compete with COO ?in binding with –N +and the aggregation of RhB decreases.Therefore,an increase in the adsorption of RhB on the APTC can be observed at pH >7.0.The variation of RhB removal with solution pH is similar to that reported previously (Arivoli et al.,2008;Guo et al.,2005),but is di ?erent from other adsorbents (Selvam et al.,2008;Sureshkumar and Namasivayam,2008).
NaCl is commonly used in textile dyeing processes as an additive to promote the adsorption capacity of the textile ?bers.Furthermore,industrial e ?uents are always contaminated by various additives such as inorganic salts.Thus,the e ?ect of ionic strength on the adsorption process was studied at three NaCl concentrations and the result is shown in Fig.4.The in?uence of ionic strength on the adsorption rate would be discussed on the Section 2.3.2.The adsorption capacity of APTC for RhB was slightly a ?ected by the presence of NaCl (Fig.4).There is a carboxyl group (–COOH)in the RhB molecule,which imparts a negative charge to the chromophore.A positive charge is also contributed by the amino group.
When
Fig.4E ?ect of ionic strength on the adsorption capacity of APTC.Conditions:initial RhB concentration 100mg /L;natural pH;temperature 25°C;adsorbent dosage 0.2g /L.
the ionic strength increased,the electrical double layer surrounding the APTC surface was compressed,resulting in a decrease in RhB adsorption onto APTC.On the other hand,NaCl could screen the electrostatic interaction of the opposite-charged groups in the zwitterionic RhB molecules,and the adsorbed amount will increase with the increase of NaCl concentration.As a result of the above two opposite in?uences,adsorption capacity of APTC for RhB is little a ?ected by ionic strength.
2.2.2Adsorption isotherm
The equilibrium adsorption isotherm is essential in describing the interactive behavior between adsorbate and adsorbent,and is important in the design of adsorption systems.Several adsorption isotherm equations are avail-able and the two important isotherms,i.e.,the Langmuir isotherm and Freundlich isotherm,are selected in this study.
The linear form of Langmuir isotherm is given by the following Eq.(1):C e q e =1bQ 0+C e
Q 0
(1)
where,C e and q e are the equilibrium liquid-phase and solid-phase of concentration,respectively;Q 0(mg /g)is the monolayer capacity of the adsorbent;and b (L /mg)is the Langmuir adsorption constant,which is related to the adsorption energy.
The Freundlich isotherm is described by the following Eq.(2):
log q e =log K F +1
n
log C e (2)
where,K F (L /g)and n are the Freundlich constants of the system,indicators of adsorption capacity and adsorption intensity,respectively.
The values of Langmuir and Freundlich parameters at di ?erent temperatures are shown in Table 2.It can be seen that the correlation coe ?cient (R 2)for Langmuir isotherm model is higher than 0.99,and q max calculated from the model is close to the experimental data.This indicates that the adsorption feature of APTC could be well described by the Langmuir isotherm.However,the Freundlich isotherm does not ?t well with the equlibrium data.In addition,it is observed that adsorption capacity is positively correlated with temperature.The maximum adsorption capacity of APTC for RhB is 307.2mg /g,which is signi?cantly higher than those reported for most of the other adsorbents (Table 3).
2.3Adsorption kinetics
In order to e ?ectively apply APTC for a particular pollutant removal from aqueous solution,it is important to study the kinetics and mechanism of the adsorption process.Moreover,information of adsorption kinetics is required for selecting the optimum operating conditions for the full-scale batch process.Herein,the kinetics of adsorption removal of RhB by APTC is studied,and in?uence of operating parameters on the adsorption rate is also evaluated.
No.8Application of activated carbon derived from scrap tires for adsorption of Rhodamine B1277 Table2Langmuir and Freundlich isotherms model constants and respective coe?cients for RhB adsorption onto APTC Temperature(°C)Experimental Langmuir model Freundlich model
q max(mg/g)Q
0(mg/g)b(L/mg)R2K F(L/g)n R2 25280.1277.8 1.310.9998134.1 4.590.9264 35288.4285.7 2.190.9993112.7 3.370.9139 45307.2312.5 3.890.9995134.2 4.730.9411
Table3Comparison of APTC adsorption capacity for RhB with other adsorbents
Adsorbent Q0(mg/g)Reference
Surfactant-modi?ed coconut coir pitch14.9Sureshkumar and Namasivayam,2008 Sago waste derived activated carbon16.1Kadirvelu et al.,2005
Sodium montmorillonite42.2Selvam et al.,2008
Jute stick powder87.7Panda et al.,2009
Carbonaceous adsorbent91.1Bhatnagar and Jain,2005
BPH activated carbon263.9Gad and El-Sayed,2009
Rice husk-based porous carbons(RHCs)383.4Guo et al.,2005
APTC307.2This work
2.3.1Kinetics study
The pseudo?rst-and second-order models were em-
ployed to perform the kinetics study.The linear form of
the pseudo?rst-order rate expression is given as Eq.(3):
ln(q e?q t)=ln q e?k1t(3)
where,k1(min?1)is the rate constant of the pseudo?rst-
order adsorption.The pseudo second-order kinetic model
is expressed by the following Eq.(4):
t q t =
1
k2q2e
+
t
q e
(4)
where,k2(g/(mg·min))is the rate constant of the pseudo second-order model.The initial rate h(mg/(g·min))can be determined using Eq.(5):
h=k2q2e(5) The validity of the two kinetic models can be checked by their linearized plots.The correlation coe?cient(R2) was used to compare the applicability of di?erent kinetic models in?tting the experimental data.Table4shows the corresponding parameters of the two kinetic models under di?erent conditions.Based on R2,the pseudo second-order kinetic model is well?tted to the experimental data. Furthermore,the q e calculated from the pseudo second-order kinetic model is close to the experimental data.
2.3.2E?ect of experimental parameters on adsorption
rate
The e?ect of contact time on adsorbed amount of RhB at three adsorbent dosages is shown in Fig.5.It is obvious that there is a rapid uptake of RhB within the?rst60 min.Then,the adsorption rate slows down gradually and no further adsorption is observed beyond300min.With the increase of adsorbent dosage,the time needed to reach equilibrium is reduced.This is due to the increase of e?cient adsorption sites at higher dosages.On the contrary,the initial rate h is reduced from68.4to17.9 mg/(g·min)when adsorbent dosage is increased from0.1 to0.5g/L(Table4).This can be attributed to the
increased Fig.5E?ect of contact time and adsorbent dosage on adsorption kinet-ics.Conditions:temperature25°C;natural pH;initial RhB concentration 100mg/L.
viscosity of the solution,which hinders the di?usion of RhB ions to the surface of APTC.
As shown in Fig.6,the removal rate of RhB is dependent on the initial RhB concentration.The rate of adsorption decreased with time until it gradually approached a
plateau Fig.6E?ect of contact time and initial RhB concentration on adsorption kinetics.Conditions:temperature25°C;natural pH;NaCl concentration 0;adsorbent dosage0.2g/L.
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Table4Parameters of kinetic models of RhB adsorption onto APTC
Adsorption q e,exp Pseudo?rst-order model Pseudo second-order model Intra-particle di?usion model
condition(mg/g)k
1
q e,cal R2k2(×103g/q e,cal R2h k i1(mg/C R2k i2(mg/C R2 (min?1)(mg/g)(mg·min))(mg/g)(g·min1/2))(g·min1/2))
Adsorbent dosage a(g/L)
0.1384.40.0125128.10.92530.463384.60.998068.47.46273.40.9314 1.81335.40.6288 0.2280.10.007992.90.98020.339284.10.999727.311.4155.30.9245 2.22239.10.8229 0.5195.60.005055.40.92730.467196.10.999617.98.4995.10.8924 1.32161.10.9209 Initial concentration b(mg/L)
50211.20.006083.60.91780.301212.70.998713.67.30103.80.9920 2.16154.90.9668 100280.10.006379.90.92060.339284.10.999727.311.4155.30.9245 2.22239.10.8229 150280.80.1030119.90.92030.360287.10.999829.611.7219.50.9957 1.64319.70.8574 Temperature c(°C)
25280.10.006379.90.92060.339284.10.999727.38.93166.90.8777 1.73249.90.7665 35288.40.0167170.60.78070.406290.80.998934.315.5114.60.9600 3.06215.40.8727 45307.20.0285241.50.58710.484310.80.998246.714.9127.10.9737 4.35207.60.9671 pH d
3.04289.20.017916
4.70.75080.422294.10.998936.514.8133.90.9666 3.79216.10.9325 7.03256.40.0158138.60.77590.404260.30.999227.514.2122.20.9902 2.82210.90.9559 10.0268.60.0165168.90.68780.399270.30.998329.112.1129.00.9576 3.83192.70.9826 Ionic strength e(mol/L)
0.001277.50.0082139.70.47310.296277.80.999422.88.96146.90.8869 1.93225.30.9215 0.010293.80.0073119.90.51800.314294.10.999527.18.42169.20.8896 1.82245.20.8513
0.100280.90.0101178.40.47080.218285.70.998917.77.72148.90.8098 2.62213.70.9058
a Conditions:temperature25°C;natural pH;initial RhB concentration100mg/L;NaCl concentration0.
b Conditions:temperature25°C;natural pH;adsorbent dosage0.2g/L;NaCl concentration0.
c Conditions:natural pH;adsorbent dosage0.2g/L;initial RhB concentration100mg/L;NaCl concentration0.
d Conditions:temperature35°C;adsorbent dosage0.2g/L;initial RhB concentration100mg/L;NaCl concentration0.
e Conditions:temperature25°C;natural pH;adsorbent dosage0.2g/L;initial RhB concentration100mg/L.
due to the continuous decrease in the concentration driving force.In addition,it can be seen from Table4that the initial rate of adsorption h was greater at higher initial RhB concentrations,as the resistance to the RhB uptake decreased with the increase of mass transfer driving force. The e?ect of temperature on adsorption was investigated under natural solution pH.As shown in Table4,the adsorption rate constant and initial rate increase with temperature.Owing to the decrease in the viscosity of the solution at higher temperature,the di?usion of RhB across the external boundary layer and in the internal pores of the APTC particle is enhanced.Therefore,the observed overall adsorption rate improves with the increase of temperature.
As presented in Table4,among the studied three initial solution pH,the initial adsorption rate h reaches maximum at pH3.04and minimum at pH7.03.The variation in the adsorption rate of RhB with pH can be elucidated by considering the dissociation form of RhB.When solution pH is lower than4.00,RhB molecules mainly exist as small cationic ions,which di?use faster and could access to most of the surface of APTC.However,deprotonation of RhB takes place with increasing solution pH,which leads to the formation of larger zwitterions.The larger zwitterions have lower di?usivities and thus a decrease in the adsorption rate is observed.When solution pH is further increased above7.00,the excessive OH?compete with COO?in binding with–N+,leading to a decrease in the aggregation of RhB.Therefore,an increase in the adsorption rate of RhB ions on the APTC is observed.
The e?ect of ionic strength on the adsorption rate of RhB is also displayed in Table4.It can be observed that the presence of inorganic salt exerted a slight in?uence on the adsorption rate of RhB.The possible reason is that the presence of the positive charge from the amino group and the negative charge from the carboxyl group,made NaCl has little e?ect on the electrical character of the RhB molecule.Therefore,the adsorption rate is little a?ected by ionic strength.
2.4Adsorption mechanism
The pseudo second-order kinetic model includes all the steps of adsorption including external?lm di?usion, internal particle di?usion,and surface adsorption.The experimentally observed adsorption rate is also the overall rate of the whole process.Therefore,it is necessary to predict the rate-limiting step of the adsorption process. Two di?usion steps are necessary for the adsorption of the adsorbate onto the adsorbent in aqueous solution,i.e., mass transfer from water to the adsorbent surface across the boundary layer and di?usion in the porous particle. Generally,?lm di?usion is often the rate-limiting step in a continuous?ow system,while for a batch reactor intra-particle di?usion is more likely the rate-limiting step (McKay,1983).The possibility of intra-particle di?usion as rate-limiting step was tested by intra-particle di?usion model,which is de?ned as Eq.(6):
q t=k ip t1/2+C(6) where,k ip(mg/(g·min1/2))is the intra-particle di?usion rate constant.The value of C is helpful in determining the boundary thickness:a larger C corresponding to a greater boundary layer di?usion e?ect(Kannan and Sundaram, 2001).
By the plots of q t versus t1/2of various initial RhB concentrations,multilinearities can be observed in Fig.7, indicating that intra-particle di?usion plays a signi?cant role but is not the only rate-controlling step.The?rst and
No.8Application of activated carbon derived from scrap tires for adsorption of Rhodamine B
1279
Fig.7Intra-particle di?usion plots under di?erent initial RhB concen-trations.Conditions:temperature25°C;natural pH;NaCl concentration 0;adsorbent dosage0.2g/L.
sharper portion is attributed to the boundary layer di?usion of RhB molecules.The second portion corresponds to the gradual adsorption stage,where intra-particle di?usion was rate-limiting step.The slope of the second linear por-tion of the plot was de?ned as the intra-particle di?usion parameter k i2.Table4shows the corresponding model ?tting parameters under di?erent conditions.The observed values of k i2are lower than k i1,indicating that intra-particle di?usion controls the adsorption rate.However,external mass transfer resistance cannot be neglected although this resistance is only signi?cant for the initial period of time. The variations of k i2with adsorption conditions are also consistent with the observations in Section2.3.2.
2.5Adsorption thermodynamics
In order to fully understand the nature of the adsorption process studied,thermodynamic studies were performed. Thermodynamic parameters such as change in free energy (?G0),enthalpy(?H0)and entropy(?S0)were calculated using the following equations:
?G0=?RT ln b(7)
ln b=?S0
R
?
?H0
RT
(8)
where,b(L/mol)is Langmuir constants at di?erent tem-peratures,R(8.314J/(K·mol))is the universal gas constant. Thermodynamic parameters at various temperatures are presented in Table5.The negative values of?G0indicate that the adsorption of RhB onto APTC is spontaneous and thermodynamically favorable.Moreover,when the temperature increases from25to45°C,?G0changes from–15.96to–19.91kJ/mol,suggesting that adsorption is more spontaneous at higher temperature.The positive value of?H0(42.82kJ/mol)indicates that the process is endothermic in nature,which is supported by the increase in the adsorption capacity of APTC for RhB with in-creasing temperature.Moreover,the positive value of?S0 (197.1J/(K·mol))suggests that the randomness increased at the solid-liquid interface during the adsorption of RhB in aqueous solution on the APTC.
Table5Thermodynamic parameters at various temperatures Temperature–?G0?H0?S0E a
(°C)(kJ/mol)(kJ/mol)(J/(K·mol))(kJ/mol) 2515.9642.82197.113.99 3517.81
4519.91
As mentioned in Section 2.3.1,the pseudo second-order kinetic model?ts well to the adsorption process of RhB by APTC.Accordingly,the rate constants(k2)of the pseudo second-order model are adopted to calculate the activation energy of the adsorption process using the Arrhenius equation(Doˇg an and Alkan,2003):
ln k2=ln A?
E a
RT
(9)
where,k2,A,E a,R and T are the rate constant of the pseudo second-order model,Arrhenius factor,activation energy, gas constant and temperature,respectively.The activation energy could be determined from the slope of the plot of ln k2versus1/T(?gure not shown).The activation energy (E a)in this study is13.99kJ/mol,further con?rming that the adsorption process is mainly physical.Therefore,?G0,?H0and E a all suggest that the adsorption of RhB onto APTC is mainly a physisorption process.
3Conclusions
The present study shows that APTC derived from solid hazardous scrap tires can be used as a potential adsorbent for the removal of RhB with a higher adsorption capacity (307.2mg/g)than most adsorbents reported in literature. Adsorption equilibrium is practically achieved within300 min.Both acidic and basic solutions are suitable for the adsorption process,and temperature exerts strong posi-tive in?uence on the adsorption process.However,ionic strength shows only slight e?ect on the adsorption process. High initial RhB concentration and low APTC dosage are favorable for adsorption https://www.sodocs.net/doc/3214563393.html,ngmuir isotherm can be successfully applied to predict the adsorption capacities of the adsorbent,and the adsorption kinetics follows the pseudo second-order rate expression.The removal rate of RhB is dependent on both external mass transfer and intra-particle di?usion.Changes in free energy of adsorption (?G0),enthalpy(?H0)and entropy(?S0),as well as the activation energy(E a)con?rm that the adsorption of RhB onto APTC is mainly a physisorption process with spontaneous,endothermic,and random characteristics. Acknowledgments
This work was supported by the National Key Technolo-gies R&D Program of China(No.2006BAC02A12),the Key Technologies R&D Program of Tianjin,China(No. 07ZCGYSH02000),and the Natural Science Foundation of Tianjin,China(No.08JCZDJC21400).
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References
Arivoli S,Sundaravadivelu M,Elango K P,2008.Removal of basic and acidic dyes from aqueous solution by adsorption on a low cost activated carbon:Kinetic and thermodynamic study.
Indian Journal of Chemical Technology,15(2):130–139. Bhatnagar A,Jain A K,2005.A comparative adsorption study with di?erent industrial wastes as adsorbents for the removal of cationic dyes from water.Journal of Colloid and Interface Science,281(1):49–55.
Cunli?e A M,Williams P T,1998.Properties of chars and activated carbons derived from the pyrolysis of used tyres.
Environmental Technology,19(12):1177–1190.
de Marco Rodriguez I,Laresgoiti M F,Cabrero M A,Torres A, Chom′o n M J,Caballero B,2001.Pyrolysis of scrap tyres.
Fuel Processing Technology,72(1):9–22.
Deshpande A V,Kumar U,2002.E?ect of method of preparation on photophysical properties of Rh-B impregnated sol-gel hosts.Journal of Non-Crystalline Solids,306(2):149–159. Doˇg an M,Alkan M,2003.Adsorption kinetics of methyl violet onto perlite.Chemosphere,50(4):517–528.
Gad H M H,El-Sayed A A,2009.Activated carbon from agri-cultural by-products for the removal of Rhodamine-B from aqueous solution.Journal of Hazardous Materials,168(2-3): 1070–1081.
Garcia I T S,Nunes M R,Carreo N L V,Wallaw W M,Fajardo
H V,Probst L F D,2007.Preparation and characterization
of activated carbons from thread of tire waste.Pol′?meros,17: 329–333.
Guo Y P,Zhao J Z,Zhang H,Yang S F,Qi J R,Wang Z C et al., https://www.sodocs.net/doc/3214563393.html,e of rice husk-based porous carbon for adsorption of Rhodamine B from aqueous solutions.Dyes and Pigments, 66(2):123–128.
Hamadi N K,Chen X D,Farid M M,Lu M G Q,2001.Adsorption kinetics for the removal of chromium(VI)from aqueous solution by adsorbents derived from used tyres and sawdust.
Chemical Engineering Journal,84(2):95–105.
Hamadi N K,Swaminathan S,Chen X D,2004.Adsorption of paraquat dichloride from aqueous solution by activated car-bon derived from used tires.Journal of Hazardous Materials, 112(1-2):133–141.
Helleur R,Popovic N,Ikura M,Stanciulescu M,Liu D,2001.
Characterization and potential applications of pyrolytic char from ablative pyrolysis of used tires.Journal of Analytical and Applied Pyrolysis,58-59:813–824.
Jang J W,Yoo T S,Oh J H,Iwasaki I,1998.Discarded tire recycling practices in the United States,Japan and Korea.
Resources,Conservation and Recycling,22(1-2):1–14. Kadirvelu K,Karthika C,Vennilamani N,Pattabhi S,2005.Acti-vated carbon from industrial solid waste as an adsorbent for the removal of Rhodamine-B from aqueous solution:Kinetic and equilibrium studies.Chemosphere,60(8):1009–1017. Kaminsky W,Mennerich C,2001.Pyrolysis of synthetic tire rubber in a?uidised-bed reactor to yield1,3-butadiene, styrene and carbon black.Journal of Analytical and Applied Pyrolysis,58:803–811.
Kannan N,Sundaram M M,2001.Kinetics and mechanism of removal of methylene blue by adsorption on various carbons –a comparative study.Dyes and Pigments,51(1):25–40. Ko D C K,Mui E L K,Lau K S T,McKay G,2004.Production of activated carbons from waste tire–process design and economical analysis.Waste Management,24(9):875–888. Lehmann C M B,Rostam-Abadi M,Rood M J,Sun J,1998.
Reprocessing and reuse of waste tire rubber to solve air-quality related problems.Energy&Fuels,12(6):1095–1099. Li S Q,Yao Q,Wen S E,Chi Y,Yan J H,2005.Properties of pyrolytic chars and activated carbons derived from pilot-
scale pyrolysis of used tires.Journal of the Air&Waste Management Association,55(9):1315–1326.
Liu S X,Zhang C,Liang X Q,Zhang X,Zhu T,2008.Patent No: CN101164876-A.
Manch′o n-Vizuete E,Mac′?as-Garc′?a A,Nadal Gisbert A, Fern′a ndez-Gonz′a lez C,G′o mez-Serrano V,2005.Adsorption of mercury by carbonaceous adsorbents prepared from rub-ber of tyre wastes.Journal of Hazardous Materials,119(1-3): 231–238.
McKay G,1983.The adsorption of dyestu?s from aqueous so-lution using activated carbon:Analytical solution for batch adsorption based on external mass transfer and pore di?u-sion.Chemical Engineering Journal,27(3):187–196.
Mui E L K,Ko D C K,McKay G,2004.Production of active carbons from waste tyres–A review.Carbon,42(14):2789–2805.
Nakagawa K,Namba A,Mukai S R,Tamon H,Ariyadejwanich P,Tanthapanichakoon W,2004.Adsorption of phenol and reactive dye from aqueous solution on activated carbons derived from solid wastes.Water Research,38(7):1791–1798.
Panda G C,Das S K,Guha A K,2009.Jute stick powder as a potential biomass for the removal of Congo Red and Rho-damine B from their aqueous solution.Journal of Hazardous Materials,164(1):374–379.
Piskorz J,Majerski P,Radlein D,Wik T,Scott D S,1999.Recovery of carbon black from scrap rubber.Energy&Fuels,13(3): 544–551.
Rivera-Utrilla J,Bautista-Toledo I,Ferro-Garcia M A,Moreno-Castilla C,2001.Activated carbon surface modi?cations by adsorption of bacteria and their e?ect on aqueous lead adsorption.Journal of Chemical Technology and Biotechnol-ogy,76(12):1209–1215.
San Miguel G,Fowler G D,Sollars C J,2002.Adsorption of organic compounds from solution by activated carbons produced from waste tyre rubber.Separation Science and Technology,37(3):663–676.
Selvam P P,Preethi S,Basakaralingam P,Thinakaran N,Sivasamy A,Sivanesan S,2008.Removal of Rhodamine B from aque-ous solution by adsorption onto sodium montmorillonite.
Journal of Hazardous Materials,155(1-2):39–44. Seneviratne H R,Charpenteau C,George A,Millan M,Dugwell D R,Kandiyoti R,2007.Ranking low cost sorbents for mercury capture from simulated?ue gases.Energy&Fuels,21(6): 3249–3258.
Skodras G,Diamantopouiou I,Zabaniotou A,Stavropoulos G, Sakellaropoulos G P,2007.Enhanced mercury adsorption in activated carbons from biomass materials and waste tires.
Fuel Processing Technology,88(8):749–758. Sureshkumar M V,Namasivayam C,2008.Adsorption behavior of direct Red12B and Rhodamine B from water onto surfactant-modi?ed coconut coir pith.Colloids and Surfaces A:Physicochemical and Engineering Aspects,317(1-3): 277–283.
Tanthapanichakoon W,Ariyadejwanich P,Japthong P,Nakagawa K,Mukai S R,Tamon H,2005.Adsorption-desorption char-acteristics of phenol and reactive dyes from aqueous solution on mesoporous activated carbon prepared from waste tires.
Water Research,39(7):1347–1353.
Teng H S,Lin Y C,Hsu L Y,2000.Production of activated carbons from pyrolysis of waste tires impregnated with potassium hydroxide.Journal of the Air&Waste Management Asso-ciation,50(11):1940–1946.
Zabaniotou A A,Stavropoulos G,2003.Pyrolysis of used automo-bile tires and residual char utilization.Journal of Analytical and Applied Pyrolysis,70(2):711–722.