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U

h0

Ecological Engineering 67 (2014) 127–133

Contents lists available at ScienceDirect

Ecological Engineering

jou rn al hom ep age: www.elsev ier .com/ locate /eco leng

ffective removal of copper ions from aqueous solution using basereated black tea waste

hih-Huang Wenga,∗, Yao-Tung Linb, Deng-Yen Honga, Yogesh Chandra Sharmac,hih-Chieh Chena, Kumud Tripathib

Department of Civil and Ecological Engineering, I-Shou University, Kaohsiung 84008, TaiwanDepartment of Soil and Environmental Sciences, National Chung Hsing University, Taichung 40227, TaiwanDepartment of Chemistry, Indian Institute of Technology (BHU), Varanasi 221005, India

r t i c l e i n f o

rticle history:eceived 30 October 2013eceived in revised form 19 January 2014ccepted 29 March 2014vailable online 20 April 2014

eywords:dsorptionase treated tea wasteoppereavy metal

a b s t r a c t

The present study investigated removal efficiency of Cu(II) ions using wasted black tea powder (BTLP)with various pretreatments. BTLP which already treated with pressure steam and base solution (0.1 MNaOH, denoted as OH-BTLP) exhibited the highest removal efficiency and the waste treated with thisprocess was used as adsorbent for further kinetic and equilibrium studies. Findings confirmed that theOH-BTLP has Cu adsorption capacity much higher than that of activated carbon. A maximum adsorptioncapacity of 43.18 mg g−1 at pH 4.4 was obtained from the Langmuir isotherms fit. Functional groupspresent on this bioadsorbent were investigated as responsible for the binding of Cu2+ ions. In the kineticadsorption experimental studies, a nearly 90% Cu removal was achieved after 10 min of contact periodand the experimental data could be described by a pseudo-2nd-order equation. Copper removal efficiencywas higher in alkaline medium at higher temperature. Since the value of activation energy is low, it is

astewater suggested that the adsorption was controlled by the process of diffusion. Thermodynamic parameterswere evaluated for present adsorption system and revealed that the adsorption is a spontaneous processat high temperature and endothermic in nature. From the perspective of waste utilization, superior copperadsorption capacity and freely abundant availability of this low-cost adsorbent, made this potentiallyapplicable for future practical applications.

© 2014 Elsevier B.V. All rights reserved.

wcauHAamcr

. Introduction

Improper treatment of metal-laden waste effluents releasedrom mining, electroplating, battery manufacturing, and metal fin-shing industries would cause serious threat to the environment,quatic and human life. The most widely used technology in treat-ng these metallic industrial effluents is chemical precipitation inonjunction with coagulation. The addition of chemicals and gen-ration of metal-laden sludge are the major concern of adaptinghis process. Furthermore, the presence of cheating agents in theffluent could increase the solidity of metal precipitates, thereby

ncreasing the difficulties of pH adjustment and decreasing thereatment efficiency. The metallic wastewaters treated by suchrocess may not meet the stringent discharge standard.

∗ Corresponding author at: Department of Civil and Ecological Engineering, I-Shouniversity, Dashu District, Kaohsiung City 84008, Taiwan. Tel.: +886 929552662.

E-mail address: chweng@isu.edu.tw (C.-H. Weng).

rcaao2e2

ttp://dx.doi.org/10.1016/j.ecoleng.2014.03.053925-8574/© 2014 Elsevier B.V. All rights reserved.

Among the processes used for the separation of metal fromastewater, adsorption is an effective technique if suitable and

hapter adsorbents are properly applied. Due to its remarkabledsorption capability, activated carbon (AC) has been commonlysed as an adsorbent for the removal of various contaminants.owever, in some undeveloped countries, high operation cost ofC has been limited its practical applicability. The inexpensive andbundant available adsorbents, such as agriculture wastes, natureaterials, and non-toxic industrial wastes can be used as activated

arbon alternatives for the metal ions removal. It is not necessary toegenerate these inexpensive adsorbents upon saturation, whereasegeneration of AC is essential. Regeneration of an adsorbent isostly and sometimes it may generate additional waste effluentnd the adsorbent may suffer a considerable loss. In recent years,

large number of researchers have been evaluated the possibility

f using these alternatives in contaminant removal (Weng et al.,007; Weng et al., 2008; Dang et al., 2009; Su et al., 2010; Scibant al., 2011; Dhir and Srivastava, 2011; Sun et al., 2011; Wu et al.,012; Kiran and Kaushik, 2012; Liu et al., 2013; Irem et al., 2013;

1 l Engin

M2

ea2tttsrpectfclsbbp

tpwso

2

2

urwfrsttpwiDlfa

TP

Na

wtttwUTlvTUmUtwtsaritc

2

oBemcaseueo0cuakdw

28 C.-H. Weng et al. / Ecologica

ittal et al., 2013; Yadav et al., 2013; Bozic et al., 2013; Li et al.,013; Gorgievski et al., 2013; Qiang et al., 2013).

Currently tea waste has increasingly gained interest as a cost-ffective adsorbent to remove various types of contaminants fromqueous solution (Amarasinghe and Williams, 2007; Hameed,009; Weng et al., 2013; Ng et al., 2013; Akar et al., 2013). Since theea leaves contains of insoluble cell walls with some specific func-ional groups which are able to uptake the contaminants, thus theea leaves can potentially use as pollutant scavengers from aqueousolutions. The functional groups which contribute in contaminantemoval process may include carboxylate, aromatic carboxylate,henolic hydroxyl, and oxyl groups of the tea leaves (Wasewart al., 2009). Different pretreatment methods and waste originsould turn out different results. Thus, knowing the effect of pre-reatments of tea waste on metal adsorption is deemed importantor decision-making. Although pretreatments will increases theost, but pretreatment of tea waste is a necessary step for control-ing tannin color and increasing adsorption capacity. Literately, thetudy of pretreatments of tea waste for metal adsorption has noteen reported yet. Utilization of tea waste as inexpensive adsor-ent for contaminant removal can convert this waste into usefulroduct but also alleviates the disposal problems.

In this study, batch adsorption experiments were carried outo evaluate the effectiveness of using tea wastes from Taiwan as aotential adsorbent for copper ions removal. In particular, the workas focusing on evaluating various pretreatments (pressure steam,

onolysis, acid washing, formaldehyde washing, and base washing)f tea waste and key parameters affecting adsorption.

. Materials and methods

.1. Tea waste

Black tea wastes (fermented) collected from a local tea man-facturing company were used for adsorption experiments. Toemove residual tea color (tannins) and impurities, the raw teaastes were first steam treated under a high pressure of 70 kPa

or 20 min using a pressure cooker. This pretreatment process wasepeated several times until the supernatant was free of color. Theteamed tea wastes were dried (80 ± 5 ◦C) in an oven for 1 day, andhen pulverized by a grinder. The milled tea wastes particles finerhan 0.149 mm were used as adsorbent. In order to find out a bestretreatment method for copper ions adsorption, the tea powderas then received several post treatments, including base wash-

ng, ultrasonic treating, acid washing, and formaldehyde washing.

etails of these pretreatments and denotation of the adsorbents are

isted in Table 1. Fresh powdered activated carbon (PAC) obtainedrom a local industrial wastewater plant was used as a benchmarkdsorbent for comparison of copper removal.

able 1reparation and denotation of the tea waste adsorbents used in this study.

Denotation Adsorbent Pretreatment of black tealeaf powder

BTLP Black tea leaf powder NoneS-BTLP Black tea leaf powder Pressure steamU-BTLP Black tea leaf powder Ultrasound (47 kHz for 1 h)H-BTLP Black tea leaf powder Acid washing (0.1 M HNO3

solution for 1 h)F-BTLP Black tea leaf powder 10% CH2O (formaldehyde

washing for 1 h)OH-BTLP Black tea leaf powder Base washing (0.1 M NaOH

solution for 1 h)PAC Powdered activated carbon Without any pretreatment

ote: All tea wastes were treated with pressure steam (70 kPa at 100 ◦C for 20 min),nd then powdered to <0.149 mm before further pretreatment applied.

t

t

q

ww

3

3

ssltf(

eering 67 (2014) 127–133

A scanning electron microscope (SEM) (Hitachi S2700, Japan)ith an electron acceleration voltage of 20 kV was used to observe

he surface physical morphology of the tea waste particles. To iden-ify the major functional groups participating in Cu binding onea wastes, Fourier transform infrared spectroscopy (FTIR) analysisas conducted on an FTIR spectrophotometer (Bruker Vector 22,SA) with the absorption spectrum between 1600 and 4,000 cm−1.he FTIR spectra were analyzed and compared before and afteroading with Cu solution. The specific surface area (SSA) and poreolume of tea wastes were determined with a Brunauer Emmetteller (BET) N2 surface area analyzer (Beckman Coulter SA3100,SA). The zeta potential of hydrolyzed tea wastes were deter-ined instrumentally using a zeta meter (Pen Kem Laser Zee 3.0,SA). To two separated 500 mL water samples of a given elec-

rolyte concentration (1 × 10−2 M NaNO3), 0.04 g of powdered teaaste was added, and the mixture was hydrolyzed one day before

he measurement of zeta potential. While the mixture was beingtirred, the solution pH was measured and adjusted by either nitriccid (HNO3) or sodium hydroxide (NaOH) solutions to cover aange from around 2.0 to 8.0. A 20 mL aliquot of the mixture wasntroduced into the chamber of the zeta meter, and the zeta poten-ial of the hydrolyzed tea waste samples was measured with aonstant voltage of 100 mV at each desired pH value.

.2. Adsorption experiments

Adsorption experiments were carried out by preparing a seriesf 100-mL Cu solution (using Cu(NO3)2·3H2O purchased from J.T.aker) containing a fixed amount of adsorbent. Since industrialffluent usually contains a certain amount of dissolved ions, toimic such impurity effects on adsorption, an electrolyte con-

entration of 1 × 10−2 M NaNO3 was added in the mixture. Afterdjusting the initial pH value with the use of either HNO3 or NaOHolutions, the mixtures were shaken on a reciprocal shaker at 150xcursions per min for 24 h. All the experiments were carried outnder isothermal conditions by placing the mixtures in a shakerquipped with a water circulation bath. After shaking, a portionf the sample was taken and immediately filtered through the.45 �m membrane filter (Advantec, Japan) and supernatant wasollected. The residual Cu ions in the supernatant were analyzedsing an atomic absorption spectrophotometer (PerkinElmer Aan-lyst 200). The experimental procedure conducted for studyinginetics of Cu adsorption was the same as described above exceptifferent contacting time intervals applied. Each batch experimentas conducted in duplicated and the average values were taken in

he data analysis.The amount of Cu adsorbed (qt(mol g−1)), at contacting time of

(min) with initial Cu concentration (Co) was calculated as:

t = (Co − Ct)VW

(1)

here Ct is the residual Cu concentration at time t; W (g) is theeight of adsorbent per V (L) of the reaction mixture.

. Results and discussion

.1. Adsorbent characterization

Some characteristic properties of selected adsorbents are pre-ented in Table 2. The result of zeta potential measurements (Fig. 1)hows that the pHzpc (zero-point charge of pH) of tea wastes are

ow (2.4). Therefore, in a solution pH of greater than the pHzpc,he tea waste particles possess a negatively charged surface, whichavors the cationic Cu ions adsorption. The chemical treatmentbase washing) of tea waste yielded increase in surface area and

C.-H. Weng et al. / Ecological Engin

Table 2The measured physicochemical properties of adsorbents.

Items BTLP OH-BTLP PAC

pH 4.75 5.07 6.65pHzpc

a 2.4 2.5 5.2Particle size (mm) <0.149 <0.149 <0.149Pore volume (cm3 g−1) 0.0202 0.0308 0.403BET-N2 specific surface area (m2 g−1) 2.04 3.61 744.6

a Zero-point charge of pH.

-10 0

-50

0

50

100

1 2 3 4 5 6 7 8

Electrolyte NaNO3 1x10-2 M

Zet

a p

ote

nti

al (m

V)

pHzpc

OH-BTL P

BTLP

ppmvc

oi

oww0us

BigrbsrwagCia

3

cicwwt

pH

Fig. 1. Zeta potential of BTLP and OH-BTLP as a function of solution pH.

orosity. Although the PAC has relatively higher surface area andore volume than that of tea wastes but the value of pHzpc (5.2) isuch higher than that of tea wastes. An adsorbent with high pHzpc

alue is normally an indication of that less adsorption affinity for

ations.

The SEM images of tea wastes exhibit heterogeneous tiny poresn the roughness and irregular layer structure (Fig. 2). Thoserregular layer structures are believed to be cellulose and the stem

aB(o

Fig. 2. SEM images of (a) BTLP at 500 magnification, (b) BTLP at 20,000 magnification

eering 67 (2014) 127–133 129

f the tea leaves. As shown, the base washing had rendered teaaste more porous than the one which treated only with streamashing. The pore volume of BTLP and OH-BTLP is 0.0202 and

.0308 cm3 g−1, respectively. The adsorbent with larger pore vol-me would expect to have higher internal surface with its activeites that can adsorb more Cu ions.

Fig. 3 shows the FTIR spectroscopic characteristics of BTLP. OnTLP, the broad strong brands at 3309.9 and 2926.7 cm−1, is an

ndicative of the existence of surface hydroxyl ( OH) and C Hroups, respectively. The peaks that appear at 1705 cm−1 are cor-esponding to the C C groups. The peaks at 1651.9 cm−1 cane attributed to carboxyl ( C O) stretching which may be corre-ponding to the lignin aromatic C C bond. Overall, FTIR analysisevealed the chemical nature of the cellulosic material. When BTLPere loaded with Cu, the spectra were shifted prominently after

dsorption including bonded OH, CH, and C C groups. We sug-ested that these three functional groups are likely to participate inu binding. Based on FTIR spectra, we can conclude that the chem-

cal nature of this cellulosic bioadsorbent remains almost the samefter Cu adsorption.

.2. Adsorption affected by pretreatment method

Fig. 4 shows a comparison of different adsorbents affected byontacting time. It appears that the amount of Cu adsorbed is min-mal if the tea waste was only treated by steam washing whenompared with other treatment method. In general, the black teaaste treated by steam washing and followed by post-treatmentith base achieved an exceptional Cu removal. In general, pre-

reated tea waste appreciably increases Cu removal. The order of Cu

dsorption capacity is as follows: OH-BTLP > F-BTLP > U-BTLP > S-TLP > BTLP > H-BTLP > PAC. When the BTLP was treated with base0.1 M NaOH), the amount of OH functional group on the surfacef BTLP was expected higher than the untreated BTLP. Based on the

, (c) OH-BTLP at 500 magnification, and (d) OH-BTLP at 20,000 magnification.

130 C.-H. Weng et al. / Ecological Engineering 67 (2014) 127–133

F squaro sion o

FCmPsi(m

3

twp9ttIaceCb

Fa4

sewcs

(

q

wvld

s

where qt,exp and qt,cal are the measured and calculated Cu adsorbedat time t, respectively, and n is the number of data points.

The fittings of PSE to the kinetic data were presented as solid

ig. 3. FTIR spectrum of BTLP (a) before and (b) after adsorption. Letters in red withf the references to color in this figure legend, the reader is referred to the web ver

TIR analysis, -OH is one of the key functional group responsible foru adsorption; the adsorption capacity of OH-BTLP was thereforeuch higher than the other treatment methods. It is known that

AC has a low adsorption capacity against heavy metal ions. In thistudy we also confirmed that OH-BTLP had Cu adsorption capac-ty much higher than that of PAC. Because the base treated BTLPOH-BTLP) achieved a highest Cu removal, so the base pretreatment

ethod was selected for further adsorption evaluation.

.3. Adsorption affected by contacting time and temperature

Fig. 5 shows the extent of Cu2+ adsorption affected by contactingime and temperature. As shown, the uptake of Cu2+ by OH-BTLPas very rapid within the first 20 min. After 20 min, the uptake of Curogressively decreased with time. Equilibrium was established at0 min at all temperatures. It is interesting to note that there werewo periods were observed in the kinetic data: the first fast adsorp-ion and a progressive adsorption achieving equilibrium thereafter.n the fast adsorption stage, around 90% Cu removal occurred inll cases. The practical implication of fast adsorption phenomenon

an facilitate the design of treatment process with energy savingxpenditure by shorten the contacting time. The fast increase inu adsorption at beginning of the adsorption process was possi-ly due to a high availability of active surface sites on OH-BTLP

0 100

2 10-5

4 10-5

6 10-5

8 10-5

1 10-4

1.2 10-4

0 20 40 60 14012010080

OH-B TLPF-BTLPU-BTLPS-BTLP

BTLPH-BTLPPAC

q (m

ol g

-1)

Time (min)

ig. 4. Comparison of various adsorbents for the effect of contacting time on Cudsorption. Conditions for all adsorbents: adsorbent 0.4 g L−1, Cu 4 × 10−5 M, pHf

.2 ± 0.2, NaNO3 1 × 10−2 M, 26 ◦C.

l

Fo4

e frame are the functional groups likely involved in Cu binding. (For interpretationf this article.)

urfaces. Similar result was obtained by other studies (Gorgievskit al., 2013; Weng and Wu, 2012). Since the readily available sitesere mostly occupied, the subsequent slow adsorption is normally

onsidered as being influenced by diffusion into the interior porepaces of OH-BTLP.

The kinetic data was analyzed using pseudo-2nd-order equationPSE) (Ho and McKay, 1998):

t = k2qe2t

1 + k2qet(2)

here k2 is the apparent rate constant of PSE (g mol−1 min−1). Thealidity of PSE in describing the kinetic data was checked using theeast-squares correlation coefficient (r2) and normalize standardeviation s (%). The s is shown as follow:

= 100 ×√∑

[qt,exp − qt,cal]2

n − 1(3)

ine in Fig. 5. Table 3 summarizes the amount of Cu adsorbed at

0

2 10-5

4 10-5

6 10-5

8 10-5

0.0001

0 20 40 60 80 10 0 12 0 14 0

38oC

26oC

16oC

4oC

q (m

ol g

-1)

Time (min)

8

8.1

8.2

8.3

0.0032 5 0.00 337 5 0.0035 0.003625

y = 9.81 - 494.1x R = 0.85 3

ln k

1/T

ig. 5. Temperature dependence of adsorption kinetics. Solid lines are the best fitf pseudo-2nd-order equation. Condition: OH-BTLP 0.4 g L−1, Cu 4 × 10−5 M, pHf

.2 ± 0.2, NaNO3 1 × 10−2 M, 26 ◦C.

C.-H. Weng et al. / Ecological Engineering 67 (2014) 127–133 131

Table 3Pseudo-2nd-order equation constants at various temperatures for Cu2+ adsorbedonto OH-BTLP.

Temp. 4 ◦C 16 ◦C 26 ◦C 38 ◦C

qe (mol g−1) 6.7 × 10−5 7.5 × 10−5 8.5 × 10−5 8.95 × 10−5

−1 −1

docr3fhdiC

pa

l

w(AwhamoEtv(vrac

3

ApdthttftCyhboWBTowe

0

20

40

60

80

100

2 3 4 5 6 7 8 9

2 g L-1

1 g L-1

0.4 g L-1

0.2 g L-1

Cu

rem

oval

(%

)

pHf

(a)

0

0.2

0.4

0.6

0.8

1

2 3 4 5 6 7 8 9pHf

Frac

tion

of C

u sp

ecie

s

Cu2+

Cu(OH)+

Cu(OH)2o

I=10-2 M

25oC

(b)

FNa

bHBi

3

q

q

wadsorbent, Ce (mol L ) is equilibrium residual Cu, Qm (mol g )is the maximum Cu adsorption capacity, and KL (L mol−1) is theadsorption affinity constant related to energy of adsorption. Fig. 7shows that the magnitude of Cu adsorption is proportional to the

0 100

9 10-5

1.8 10-4

2.7 10-4

3.6 10-4

4.5 10-4

0 100 9 10-5 1.8 10-4 2.7 10-4 3.6 10-4

38oC

26oC

16oC

4oC

q (m

ol g-1)

-1

8.2

8.3

8.4

8.5

0.00325 0.0 0337 5 0.003 5 0.0 0362 5

y = 9.5- 340.8x R = 0.944

ln K

1/T

k2 (g mg min ) 3150 3220 3380 3850r2 0.997 0.997 0.996 0.999s (%) 4.69 4.23 5.24 2.23

ifferent temperatures and the corresponding fitting parametersf PSE model. The small s and high r2 values indicate that the dataan be described with this model. It is evident that the adsorptionate is greatly affected by the temperature. The rate increased from.15 × 103 to 3.85 × 103 g mg−1 min−1 when temperature increasedrom 4 to 38 ◦C, indicating that the adsorption process is faster atigher temperature. An increase in temperature may increase theriving force of diffusion across the external boundary layer and

ncrease the rate of diffusion within the pores. Consequently, moreu ion easily enters the interior pore of OH-BTLP.

The rate constants, k2, listed in Table 3 can be related to tem-erature by Arrhenius equation and were used to determine thectivation energy (Ea) of this adsorption process.

n k2 = (ln A) − Ea

RT(4)

here A is the pre-exponential factor, R is the universal gas constant8.315 J mol−1 K−1), and T is the absolute temperature (K). From therrhenius plot (the inset graph in Fig. 5), A was found to be 9.81,hich suggested that the rate of adsorption would increase at aigher temperature. The slope is equal to −Ea/R from which thepparent activation energy of the adsorption process was deter-ined to be 4.12 kJ mol−1. The magnitude of Ea explains the type

f adsorption, i.e., physical or chemical mechanism. Normally thea value for physical adsorption is less than 4.0 kJ mol−1 because ofhe bonding forces involved in physical adsorption are weak. The Ea

alue for chemical adsorption is usually higher than 4–6 kJ mol−1

Baysal et al., 2009) while a diffusion-controlled process has acti-ation energy less than 25–30 kJ mol−1 (Ho and McKay, 1998). Theelatively low Ea value obtained in this study suggested that thedsorption of Cu2+ onto OH-BTLP was a diffusion-controlled pro-ess and the reaction involved in physisorption mechanism.

.4. Adsorption affected by pH

The solution pH plays a crucial role in affecting Cu adsorption.dsorption affected by pH was carried out by varying solutionH and tea waste concentration. Fig. 6a shows the results of pHependence of the adsorption. A sharply increase of Cu adsorp-ion was observed when pH increased from 2.5 to 6.0. Since copperydroxide precipitate forms at pH >7.0 (Fig. 6b), adsorption ishe only reaction contributing in Cu removal. Above pH 7.0, morehan 95% of Cu removal was occurred, which could be resultedrom the concurrent of Cu(OH)2(s) precipitation along with adsorp-ion. It appears that pH is an important parameter affecting theu removal. Changes in solution pH could not affect the hydrol-sis of Cu ion species, it can also govern the ionized species of aydrolyzed adsorbent and the surface dependable charge of adsor-ent. Consequently it ultimately governs the adsorption affinityf the adsorbent. As shown in Table 2 the pHzpc of OH-BTLP is 2.5.hen the solution pH is greater than 2.5, the negative charged OH-

TLP surface provides affinity site for the uptake of cationic Cu ions.

he extend of Cu adsorption is also associated with the magnitudef charge density on the adsorbent surface. Increasing solution pHould also increase the negative charge density of OH-BTLP, which

nhances Cu adsorption by increasing electrostatic attraction force

FS1

ig. 6. (a) Cu adsorption onto OH-BTLP as a function of pH. Condition: Cu 5 × 10−5 M,aNO3 1 × 10−2 M, 26 ◦C, contacting time 2 h. (b) Distribution diagram of Cu speciess a function of pH for ionic strength of 10−2 M.

etween the OH-BTLP surface and Cu ions. At pH less than 2.5, more+ ion competes with free Cu2+ ion for the active surface sites ofTLP and less functional groups (i.e., OH) are ionized. Therefore,

t is difficult for BTLP to uptake Cu ions.

.5. Adsorption isotherms

The equilibrium adsorption data was described by most fre-uently used Langmuir isotherm:

= KLQmCe

1 + KLCe(5)

here q (mol g−1) is the amount of Cu adsorbed per unit gram of−1 −1

Ce (mol L )

ig. 7. Isotherm for Cu(II) adsorption onto OH-BTLP at different temperatures.olid lines are the best fit of Langmuir isotherm. Conditions: pHf 4.4 ± 0.2; NaNO3

× 10−2 M.

132 C.-H. Weng et al. / Ecological Engin

Table 4Langmuir isotherm constants for adsorption of Cu2+ onto OH-BTLP.

Temp. 4 ◦C 16 ◦C 26 ◦C 38 ◦C

Qm (mol g−1) 5.5 × 10−4 6.0 × 10−4 6.8 × 10−4 7.3 × 10−4

KL (L mol−1) 3190 4050 4350 4430r2 0.989 0.992 0.996 0.997

Table 5Thermodynamic parameters for adsorption of Cu2+ onto OH-BTLP.

Temp. 4 ◦C 16 ◦C 26 ◦C 38 ◦C

�Go (kJ mol−1) −19.04 −19.99 −20.71 −21.72

tiwthib

(l

�

l

TiFppn

iftt�st(abtfbai

3

aBi2otOsnbtT

TC

�Ho (kJ mol−1) 2.89 2.89 2.89 2.89�So (J K−1 mol−1) 79.1 79.1 79.1 79.1

emperature and results obtained were fitted in Eq. (5). As shownn Fig. 5b, in this pH region (4.4 ± 0.2) investigated, the Cu2+ ion

ould be the major adsorbed cationic copper species. Table 4 listedhe calculated constants (i.e., Qm and KL) for Langmuir models. Theigh correlation coefficient (i.e., r2 > 0.98) and the well-fitted lines

n Fig. 7, confirming the equilibrium data could be well representedy Langmuir isotherm.

The changes in free energy (�Go), enthalpy (�Ho), and entropy�So) for the adsorption of Cu2+ onto BTLP were calculated as fol-ows:

Go = −RT × ln(KL) (6)

n(KL) = �So

R− �Ho

RT(7)

he values of �Ho and �So can be obtained from the slopes andntercepts, respectively, of the van’ Hoff plot (the inset graph in

ig. 7). Thermodynamic functions calculated as a function of tem-erature are presented in Table 5. The negative value of �Go andositive value of �So indicate that the adsorption process is sponta-eous with a high preference of Cu2+ for the OH-BTLP. The increase

issw

able 6omparison of maximum adsorption capacities of various adsorbents for Cu(II) ions.

Adsorbents pH

BiomassBase treated black tea leaf powder 4.4

Tea waste (washed by hot water) 5.5

Agaricus bisporus (mushroom biomass) 5.0

Pineapple leaf powder 5.0

wheat straw 6.0

Neem leaves 6.0

Rice husk 6.0

Lignin 5.5

Polyethylenimine modified aerobic sludge 5.5

Activated carbonActivated carbon 4.0

Activated carbon cloth 4.0

Carbon nanotubes (CNTs) 5.0

Hazelnut shell activated carbon 6

Sulfonated magnetic graphene oxide composite 5.0

CNTs immobilized by calcium alginate 5.0

PolymerChitosan-coated sand 4.5

Chitosan–zeolite composites 5.0

Chitosan–zeolite composite crosslinked with epichlorohydrin 5.0

Minerals/oxides/wastesRed mud 5.5

Fly ash 4.5

Spent activated clay 5.0

Anatase mesoporous TiO2 nanofibers 6.0

EDTA-Fe3O4 magnetic nano-particles 6.0

eering 67 (2014) 127–133

n �Go with increase in temperature implies that the process isavorable at higher temperature and spontaneity increases withhe rise in temperature. The positive value of �Ho confirms thathe adsorption process is endothermic in nature. The low value of

Ho implies loose bonding between the Cu2+ ion and the OH-BTLPurface (Horsfall et al., 2006). For an ion-exchange mechanism,he bonding energy ranges typically from 7.99 to 15.98 kJ mol−1

Ho et al., 2002). �Go values below 15.98 kJ mol−1 are considereds physical adsorption which involves in electrostatic interactionetween adsorption sites and the metal ions. �Go values higherhan 31.9 kJ mol−1 are consistent with charge sharing or transferrom the adsorbent surface to the metal ion to form a coordinateond (Abia Jr. and Spiff, 2006). The magnitude of �Go is slightlybove the physical adsorption range, suggesting that the adsorptions a typical physical process enhanced by electrostatic attraction.

.6. Comparison of various adsorbents for Cu adsorption

Table 6 demonstrates a comparison between maximum Cu(II)dsorption capacity, Qm, of various type of adsorbents and OH-TLP. The adsorption capacity of base treated BTLP (43.18 mg g−1)

s much higher than the Turkey tea waste (8.64 mg g−1) (Cay et al.,004). Differences in Cu adsorption capacities are due to in partf variation in properties from the origin of the tea wastes andhe preparation of the adsorbents. The Cu adsorption capacity ofH-BTLP is relatively high when compared with other inexpen-

ive adsorbents. Most recently developed materials, such as carbonanotubes immobilized by calcium alginate (Li et al., 2010), haveeen highlighted superior adsorption capacity for Cu; however,he high-cost of this modified adsorbent may limit its implication.he tea wastes have an exceptional Cu adsorption capacity and

t can be obtained cheaply in large quantity. When the OH-BTLPaturated with Cu, it can be incinerated to collect Cu. Our resultshow the possible implications of OH-BTLP for removal of Cu fromastewaters.

Qm (mg g−1) Ref.

43.18 This study8.64 Cay et al. (2004)9.11 Ertugay and Bayhan (2010)9.28 Weng and Wu (2012)

11.43 Dang et al. (2009)17.5 Singh and Das (2013)17.9 Singh and Das (2013)22.87 Guo et al. (2008)71.2 Sun et al. (2011)

3.56 Machida et al. (2005)13.3 Huang and Su (2010)26.41 Li et al. (2010)48.64 Demirbasa et al. (2009)56.9 Hu et al. (2013)84.88 Li et al. (2010)

8.18 Wan et al. (2010)25.61 Wan Ngah et al. (2013)51.32 Wan Ngah et al. (2013)

5.34 Nadaroglu et al. (2013)9.6 Wu et al. (2012)

10.9 Weng et al. (2007)12.8 Vu et al. (2012)46.3 Liu et al. (2013)

l Engin

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iprfiogmplammiwtedesst

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D

E

G

G

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H

H

I

K

L

L

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C.-H. Weng et al. / Ecologica

. Conclusions

In summary, black tea waste treated with base solution exhib-ted an exceptional Cu(II) adsorption capability amongst the testedretreatment methods. A rapid Cu adsorption with nearly 90%emoval achieved within 10 min contacting time. The kinetic datatted well to pseudo-2nd-order equation. Based on the low valuesf activation energy, it is suggested that the adsorption process isoverned by diffusion and the reaction involved in physisorptionechanism. Copper adsorption was highly dependent on solution

H and the removal efficiency was higher in alkaline range. Equi-ibrium data were correlated well with Langmuir isotherm modelnd a maximum Cu adsorption capacity of 43.18 mg g−1 was deter-ined for base treated tea waste. Analysis of FTIR showed that theain functional groups of black tea waste participating in Cu bind-

ng were OH, CH, and C C groups. Thermodynamic parametersere evaluated for present adsorption system and showed that

he adsorption is a spontaneous process at high temperature andndothermic in nature. Finding reveals that tea waste, an abun-antly available waste, can be used an inexpensive adsorbent forffectively removal of Cu from aqueous solution. Because tea con-umption is worldwide and tea wastes can easily be acquired, it ispeculated that tea waste has high potential for practical applica-ions in treating Cu laden wastewaters.

cknowledgment

This study was supported by the National Science Council ofaiwan (Grant No. NSC 96-2221-E-214-013-MY3).

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