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Enhanced chitosan beads-supportedFe0-nanoparticles for removal of heavy metals fromelectroplating wastewater in permeable reactivebarriers

Tingyi Liu a, Xi Yang a, Zhong-Liang Wang a,b,*, Xiaoxing Yan b

a Tianjin Key Laboratory of Water Resources and Environment, Tianjin Normal University, Tianjin 300387, PR Chinab College of Urban and Environment Science, Tianjin Normal University, Tianjin 300387, PR China

a r t i c l e i n f o

Article history:

Received 20 December 2012

Received in revised form

21 August 2013

Accepted 1 September 2013

Available online xxx

Keywords:

Nanoscale zero-valent iron (NZVI)

Permeable reactive barriers (PRBs)

Ethylene glycol diglycidyl

ether (EGDE)

Heavy metals

Electroplating wastewater

* Corresponding author. Tianjin Key LaboratChina. Tel./fax: þ86 22 23766256.

E-mail addresses: [email protected]

Please cite this article in press as: Liu, Tmetals from electroplating wastewaterj.watres.2013.09.006

0043-1354/$ e see front matter ª 2013 Elsevhttp://dx.doi.org/10.1016/j.watres.2013.09.006

a b s t r a c t

The removal of heavy metals from electroplating wastewater is a matter of paramount

importance due to their high toxicity causing major environmental pollution problems.

Nanoscale zero-valent iron (NZVI) became more effective to remove heavy metals from

electroplating wastewater when enhanced chitosan (CS) beads were introduced as a sup-

port material in permeable reactive barriers (PRBs). The removal rate of Cr (VI) decreased

with an increase of pH and initial Cr (VI) concentration. However, the removal rates of Cu

(II), Cd (II) and Pb (II) increased with an increase of pH while decreased with an increase of

their initial concentrations. The initial concentrations of heavy metals showed an effect on

their removal sequence. Scanning electron microscope images showed that CS-NZVI beads

enhanced by ethylene glycol diglycidyl ether (EGDE) had a loose and porous surface with a

nucleus-shell structure. The pore size of the nucleus ranged from 19.2 to 138.6 mm with an

average aperture size of around 58.6 mm. The shell showed a tube structure and electro-

plating wastewaters may reach NZVI through these tubes. X-ray photoelectron spectro-

scope (XPS) demonstrated that the reduction of Cr (VI) to Cr (III) was complete in less than

2 h. Cu (II) and Pb (II) were removed via predominant reduction and auxiliary adsorption.

However, main adsorption and auxiliary reduction worked for the removal of Cd (II). The

removal rate of total Cr, Cu (II), Cd (II) and Pb (II) from actual electroplating wastewater was

89.4%, 98.9%, 94.9% and 99.4%, respectively. The findings revealed that EGDE-CS-NZVI-

beads PRBs had the capacity to remediate actual electroplating wastewater and may

become an effective and promising technology for in situ remediation of heavy metals.

ª 2013 Elsevier Ltd. All rights reserved.

1. Introduction persistent, bioaccumulative and harmful substances (US EPA,

Electroplating wastewater contains many kinds of heavy

metals, such as Cr, Pb, Cu, Cd, and etc., which are considered

ory of Water Resources

kleg.cn, [email protected]

., et al., Enhanced chitoin permeable reactive

ier Ltd. All rights reserved

1998; Algarra et al., 2005). Due to the serious threat to human

health and ecological systems, these contaminants must be

and Environment, Tianjin Normal University, Tianjin 300387, PR

, [email protected] (Z.-L. Wang).

san beads-supported Fe0-nanoparticles for removal of heavybarriers, Water Research (2013), http://dx.doi.org/10.1016/

.

mailto:[email protected]



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removed from wastewaters before discharge to the environ-

ment (Panayotova et al., 2007).

Various remediation technologies have been developed for

the removal of the metals from wastewaters (Fu and Wang,

2011). One of the most promising and effective remediation

technologies is the use of permeable reactive barriers (PRBs)

filled with reactive material(s) for the treatment of contami-

nated groundwater (Thiruvenkatachari et al., 2008). Owing to

low production costs and high efficiency for removal of a wide

range of contaminants, zero-valent iron (ZVI) is usually used

as a reactivematerial in engineered PRBs in the form ofmicro-

scale powders and/or macro scale filings/granules (Choi et al.,

2007; Farrell et al., 2000; Scott et al., 2011).

Because of its extremely small particle size, large surface

area, and high reactivity, nanoscale zero-valent iron (NZVI) has

been introduced into wastewaters treatment to remove heavy

metals with a much higher efficiency than normal iron pow-

ders (Cao and Zhang, 2006; Geng et al., 2009; Kanel et al., 2006).

NZVI was applied to remediate wastewaters with a higher

removal efficiency in PRBs. However, few studies used NZVI as

the reactivemedia in PRBs.Oneof the reasonsmaybe thatNZVI

particles are not easily contained in PRBs due to their extremely

small particle size (Joo et al., 2004; Thiruvenkatachari et al.,

2008). To overcome these problems, it may be advisable to

support NZVI particles on macro-scale and stable composite

beads without reducing their reactivity. More recently, NZVI

has been supported by chitosan (CS) beads to prepare com-

posite beads with a mean diameter of 3.1 mm (Liu et al., 2010,

2012).Most studies have focused onNZVI synthesis (Zhan et al.,

2009), modification (Johnson et al., 2009), and the transport and

fate of NZVI in porous media (Phenrat et al., 2009), thus infor-

mation has been lacking on using CS-NZVI composite beads

with a good mechanical strength in PRBs.

NZVI has shown high efficiency to remove only one or two

kinds of heavy metals in wastewater (Kanel et al., 2006; Liu

et al., 2009; Manning et al., 2007; Ponder et al., 2000). Howev-

er, the interactions between metal ions affected the removal

efficiency when several heavy metals co-existed in the

wastewaters (McKenzie, 1980; Shama et al., 2010).

The goal of the research is to prepare a new and stable

system, chitosan/Fe0-nanoparticles beads, as the reactive

materials in permeable reactive barriers, for the remediation

of electroplating wastewater, containing four heavy metals

(Cr, Cu, Cd and Pb). Themain objectives were to: (1) synthesize

and characterize the new and stable CS-NZVI beads; (2) eval-

uate the removal efficiency of the co-existing heavy metals by

enhanced chitosan/Fe0-nanoparticles beads PRBs under

different experimental conditions and (3) investigate the

elemental composition and their valence variation during

remediation process to reasonably conclude the removal

mechanism of co-existing heavy metals in the chitosan/Fe0-

nanoparticles beads PRBs.

2. Materials and methods

2.1. Materials and chemicals

Cellulose powder (20 mm) and chitosan flakes (75% deacety-

lated) were purchased from Sigma Co. NZVI particles with a

Please cite this article in press as: Liu, T., et al., Enhanced chitometals from electroplating wastewater in permeable reactivej.watres.2013.09.006

mean diameter of 45.2 nm were purchased from Nanjing

Emperor Nano Material Co., Ltd. Ethylene glycol diglycidyl

ether (EGDE), K2Cr2O7, CuCl2, CdCl2 and PbCl2 were provided

by First Chemical Reagent Manufactory (Tianjin, China). All

other chemicals were of analytical grade purity.

2.2. Preparation of EGDE-CS-NZVI beads

CS-NZVI beads were prepared according to the procedures

described in detail elsewhere (Li and Bai, 2005; Liu et al., 2010).

Briefly, chitosan flake (2.0 g) was dissolved in 100mL 1.0% (v/v)

acetic acid solution at 60 �C and 220 revolutions per min (rpm)

for 5 h. Then, a 1.0 g amount of cellulose powerwas added into

the chitosan solution and the mixing was continued for

another 5 h at 30 �C and 220 rpm. As the chitosan-cellulose

solution was cooled down to 20 �C, a 1.0 g amount of NZVI

was gently added into the solution. Then, the mixture was

promptly dropped into a 2 mol/L NaOH solution to form

chitosan-cellulose-NZVI beads. The beads were allowed to

stand in the deoxygenated NaOH solution for 24 h for hard-

ening and then washed with deionized water. The CS-NZVI

beads were stored in deionized water for further use.

The beads in stock were put into a beaker with 100 mL

deionizedwater, adjusting pH to 12 by adding 0.1mol/L NaOH.

Then, a 0.8 g of EGDE solution was introduced into the beaker.

After continuous agitation at 60 �C for 4 h in a thermostatic

water bath, the mixture was cooled down to room tempera-

ture, and the EGDE-CS-NZVI beads were washed extensively

with deionized water to remove any residual cellulose and

EGDE. These beads were stored in deionized water for further

use. The beads prepared in this way had an average of

3.0 � 0.04 mm and the water content of the studied material

was 89.5% in wet. The whole process was carried out in a ni-

trogen atmosphere.

2.3. PRBs experimental set-up and procedure

A laboratory-scale PRBs system was designed using a plex-

iglass columnwith 50 cm length and 15mm internal diameter.

The columnwas filledwith the prepared EGDE-CS-NZVI beads

as the reactive media and the length of the filler was about

35.6 cm. A 3 cmheight of quartz sand (about 0.5mmdiameter)

was used to fix the fillers on the top and the bottom, respec-

tively. Electroplating wastewater was continuously pumped

into the reactive material column with a downflow mode by

peristaltic pump at a flow rate of 60 mL/h. Every 10 min, 1 mL

sample was withdrawn using disposable syringes and filtered

through a 0.42 mm micro-hole filter. Only one column was

constructed due to logistical constraints, meaning that a total

of PRBs experimental runs were conducted on the column.

Each treatment was replicated three times, with the column

completely emptied and repacked between each experiment.

After removing themedia, the columnwas soaked in 0.1mol/L

HCl for 24 h and then washed with deionized water 3 times.

2.4. Effects of different experimental conditions on theremoval efficiency of heavy metals

The pH of the solutions was one of themost important factors

in removing heavy metals. The pH was adjusted to 2.88, 4.09,




wat e r r e s e a r c h x x x ( 2 0 1 3 ) 1e1 0 3

5.12, 6.06, 7.02, 8.06 and 9.20 by adding 0.1 mol/L HCl and

NaOH, respectively.

In addition, the concentration of heavy metals was also

varied at four concentrations. The highest concentration of Cr

(VI), Cu (II), Cd (II) and Pb (II) was 100, 100, 75 and 50 mg/L,

respectively. These concentrations are extremely high

compared with the maximum concentrations allowed in

groundwater by the National Quality Standard for Ground-

water in China (GB/T 14848-93) (GAQSIQ, 1993), which permit

0.1mg/L for Cr (VI), 1.5mg/L for Cu (II), 0.01mg/L for Cd (II) and

0.1 mg/L for Pb (II). However, the main goal of the test was to

evaluate the performance of EGDE-CS-NZVI beads PRBs under

extreme contaminated conditions.

2.5. Removal capacity of heavy metals by EGDE-CS-NZVI beads PRBs

Removal capacity of heavy metals was conducted and the

concentration of Cr (VI), Cu (II), Cd (II) and Pb (II) in simulated

electroplating wastewater was 20, 20, 15 and 10 mg/L,

respectively. The wastewater was continuously pumped into

the reactive material column with a downflow mode for 10 h.

Samples were withdrawn using disposable syringes at certain

time intervals.

The Thomas model is used to predict the column break-

through capacities. The expression of the Thomas model for

an adsorption column is as follows (Fu and Viraraghavan,

2003; Vijayaraghavan et al., 2005):

Cout

Cin¼ 1

1þ exp�kTHQ

�qeqX� CinVout

�� (1)

where Cout and Cin represent the concentration of the effluent

and influent, respectively. kTH is the Thomas rate constant

(mL/min mg), qeq is the maximum solid-phase concentration

of the solute (mg/g), Vout is the effluent volume (mL), X is the

mass of adsorbent (g), and Q is the flow rate (mL/min).

The linearized form of the Thomasmodel is as equation (2)

(Kavak and Ozturk, 2004):

ln

�Cin

Cout� 1

�¼ kTHqeqX

Q� kCinVout

Q(2)

The kinetic coefficient kTH and the adsorption capacity of

the bed qeq can be determined from a plot of ln[(Cin/Cout) �1]

against t at a given condition.

2.6. EGDE-CS-NZVI beads characterization andanalytical methods

The concentration of each heavy metal was measured using

inductively coupled air-acetylene flame atomic emission

spectrometry (AAF-AES) (WFX-130, BJR Co.). The EGDE-CS-

NZVI beads were dried by a vacuum freeze drier (BYK FD-

1A-50, China) at �52 �C for 5 h. Morphological analysis of the

beads was then performed using a scanning electron micro-

scope (SEM) with energy-dispersive X-ray (EDS) detection

(SEM/EDS, FEI Nova NanoSEM 230). The X-ray photoelectron

spectroscope (XPS, PHI 5000 Versa Probe) analysis was

employed to investigate the elemental composition of the

EGDE-CS-NZVI beads before and after heavymetals reduction.


The typical wide scan XPS spectra for final products were also

investigated.

2.7. Application of EGDE-CS-NZVI beads PRBs to removeheavy metals from electroplating wastewater

To explore the feasibility of the removal of heavy metal ions

from wastewater, EGDE-CS-NZVI beads PRBs was used to

remediate actual electroplating wastewater collected from an

electroplate factory’s sewage outfall (Tianjin, China). The

wastewater was not treated by any means before being

introduced into the EGDE-CS-NZVI-beads PRBs.

3. Results and discussion

3.1. Mechanical property of EGDE-CS-NZVI beads

Mechanical strength of EGDE-CS-NZVI beads was determined

following a previously reported method (Guo et al., 2004). The

deformation ratio is only 2% when the stirring speed reached

800 rpm. In comparisonwith other studies (Guo et al., 2004; Liu

et al., 2012), the conclusion can be reasonably generalized that

crumpling ratios are significantly reduced after cross-linking

reaction, which indicates that the mechanical strength of

EGDE-CS-NZVI beads is enhanced. Thus, it is likely that the

new and stable EGDE-CS-NZVI beads will be suitable as the

reactive materials in PRBs.

3.2. Removal capacity of heavy metals by EGDE-CS-NZVI beads PRBs

The results of the removal capacity of heavymetals are shown

in Fig. 1. Within the reaction time of 6 h, the heavy metals Cr

(VI), Cu (II), Cd (II) and Pb (II) can be efficiently removed and all

of the removal rates are higher than 96%. Then, the removal

rates generally decreasedwith increasing reaction time, as the

redox reaction between heavy metals and NZVI was a chem-

ically controlled and irreversible process (Shi et al., 2011). It

also can be seen that there is a steep decrease in the removal

rate of Cr (VI) after 6 h (Fig. 1). The pH gradually increased

during the reaction process (Table 1), resulting in a decrease in

Cr (VI) removal rate (Boddu et al., 2003). Similar phenomena

have been observed in other NZVI systems (Liu et al., 2010).

However, a significant decrease in the removal rate of Cu (II),

Cd (II) and Pb (II) was not observed after 6 h because of the

removal rate of Cu (II), Cd (II) and Pb (II) increasing with an

increase of pH (Lai and Chen, 2001).

As the column saturation/uptake capacity was not

observed in this study, a Thomas model is used to predict the

column breakthrough capacities (at Ce/C0 ¼ 1), described in

detail in other studies (Reynolds and Richards, 1996). Ac-

cording to Thomas model, the removal capacity at the

breakthrough point is 44.8, 67.2, 82.6 and 55.8 mg/g for Cr, Cu,

Cd and Pb, respectively. The removal capacities obtained in

our study are much higher than the results using commercial

iron filings or NZVI particles (Genc-Fuhrman et al., 2008;

Ponder et al., 2000). It is mainly attributed to the fact that

the EGDE-CS-NZVI beads may form the surface films in the

PRBs, which in turn causes higher diffusion and adsorption




0 2 4 6 8 100.0

0.2

0.4

0.6

0.8

1.0 Cr Cu Cd Pb

Cou

t/Cin

Time (h)

Fig. 1 e Removal capacity of heavy metals by EGDE-CS-

NZVI beads PRBs. Initial concentration: 20 mg/L Cr (VI),

20 mg/L Cu (II), 15 mg/L Cd (II), and 10 mg/L Pb (II); the

concentration of NZVI in CS-NZVI: 10.0 g/L; pH: 6.4;

temperature: 20 �C. Cout and Cin represented the

concentration of the effluent and influent, respectively.

Error bars represent the standard deviation of the

measurements.

4 6 8 100.00

0.05

0.10

Cou

t/Cin

Cr Cu Cd Pb


than batch experiments (Lai and Chen, 2001). The biofilm has

an influence on the transport of stabilized NZVI (Lerner et al.,

2012). Due to microbial degradation, ZVI integrated

sequencing batch reactor (SBR) resulted in the increased

organic removal efficiency compared to the control (Lee et al.,

2010). NZVI stimulatedmethanogenic activity while inhibiting

biological dechlorination in a mixed culture containing Deha-

lococcoides spp (Kirschling et al., 2010; Xiu et al., 2010).

The results indicated that EGDE-CS-NZVI beads PRB were

effective to remove various heavy metals and a potential

promising candidate for applications to in situ environmental

remediation.

3.3. Effect of pH

A change of pH can influence the reaction rate of iron oxida-

tion and corrosion (Alowitz and Scherer, 2002) and heavy

metals can be removed through oxidation or/and complexa-

tion with the oxide and hydroxides of iron (Melitas et al., 2001;

Shokes and Moller, 1999). The dominant forms of heavy

metals in aqueous solution were also affected by pH (Mohan

and Pittman, 2006). Thus pH of electroplating wastewater

played an important role in removing of heavy metals.

The effect of pH on heavy metals removal was conducted

and the result is shown in Fig. 2. It is obvious that the removal

Table 1e The change of the solution pH during the courseof adsorption. Initial concentration of Cr (VI): 20 mg/L, Cu(II): 20 mg/L, Cd (II): 15 mg/L, and Pb (II): 10 mg/L; NZVI:10.0 g/L; pH: 2.88; temperature: 20 �C.

Time (min) 0 10 20 30 40 50 60

pH 2.88 3.84 4.92 5.12 5.58 6.18 6.62


rates of all heavy metals are higher than 91.8% (Fig. 2), which

suggests that EGDE-CS-NZVI beads as a reactivemedia in PRBs

is highly efficient to remove heavy metals from aqueous so-

lutions. It is further noted that with an increase of pH, removal

rate of Cr (VI) decreased but the removal rates of Cu (II), Cd (II)

and Pb (II) increased. HCrO4- predominates at pH between 1.0

and 6.0, and CrO42� pH above about 6.0 (Mohan and Pittman,

2006). At lower pH the beads were positively charged due to

the protonation of amino groups, while Cr (VI) existed mostly

as an anion leading to the electrostatic attraction between Cr

(VI) and the beads (Boddu et al., 2003). Furthermore, the lower

pH could prevent the formation of Fe(III)eCr(III) precipitate.

Thus Cr (VI) removal rate decreasedwith an increase in pH. On

the other hand, with increased hydroxyl groups, the number

of negatively charged sites was improved, leading to the

enhanced attraction force between heavy metals (Cu (II), Cd

(II) and Pb (II)) and these beads surface. Therefore, the removal

amount of Cu (II), Cd (II) and Pb (II) was increased. The trend is

consistent with the reported results by other researchers who

investigated the adsorption of heavy metals on the iron-

coated sand, CS-NZVI beads and a composite chitosan bio-

sorbent (Boddu et al., 2003; Lai and Chen, 2001; Liu et al., 2010).

The change of the solution pH during the reaction was also

recorded and the result is shown in Table 1 (Initial concen-

tration of Cr (VI): 20 mg/L, Cu (II): 20 mg/L, Cd (II): 15 mg/L, and

Pb (II): 10 mg/L; NZVI: 1.0 g/L; pH: 2.88; temperature: 20 �C). Itcan be seen fromTable 1 that the solution pH is increasedwith

increasing reaction time. The oxidation of iron and dissolution

of Fe(III)eCr(III) precipitate consumed Hþ in the solution,

which led to the increase of pH (Alowitz and Scherer, 2002).

However, the removal of Cu (II), Cd (II) and Pb (II) also

consumedhydroxyl groups. As a result, the final pH value near

neutrality was 6.62. This is consistent with the results as

observed in Fig. 2.

pH value

Fig. 2 e Effect of pH value on the removal of heavy metals

by EGDE-CS-NZVI beads PRBs. Initial concentration: 20 mg/

L Cr (VI), 20 mg/L Cu (II), 15 mg/L Cd (II), and 10 mg/L Pb (II);

the concentration of NZVI in CS-NZVI: 10.0 g/L; pH: 6.4;

temperature: 20 �C. Cout and Cin represented the



measurements.





3.4. Effect of initial concentrations of heavy metals

Heavy metals pollution incidents have occurred repeatedly in

recent years (Arao et al., 2010). The concentrations of heavy

metals in the incidents were extremely high compared with

the maximum concentrations allowed in groundwater. Then,

studying on the effect of initial concentrations of heavy

metals on the removal efficiency is very important to the ap-

plications of EGDE-CS-NZVI beads PRBs. Thus, the effect of

initial concentrations of heavy metals was estimated and the

result is shown in Fig. 3. It can be observed that the removal

rate of Cr (VI), Cu (II), Cd (II), and Pb (II) decreases with an in-

crease of the initial Cr (VI) concentration. With a fixed adsor-

bent dose, the total available adsorption sites are limited thus

leading to a decrease in removal rate of adsorbate corre-

sponding to an increased initial adsorbate concentration

(Hiemstra and Van-Riemsdijk, 1999).

At the lower concentration (less than 40 mg/L), heavy

metals are removed in the order Cd (II) > Cu (II) > Pb (II) > Cr

(VI) (Inset of Fig. 3 (a) and (b)). As the concentration increases,

the removal order is changed into Pb (II) > Cu (II) > Cd (II) > Cr

(VI) (Fig. 3 (c) and (d)). Iron has greater affinity with Pb (II) than

Cu (II) in the process of adsorption/oxidation (Lai and Chen,

2001). The similar phenomenon had been reported where

heavy metals were adsorbed in the order Pb (II) > Cu (II) > Zn

(II) > Cd (II) by hematite (Schwertman and Taylor, 1989). Using

0 1 2 30.0

0.2

0.4

0.6

0.8

1.0

Cou

t/Cin

Time (h)

(a)

0.0 0.5 1.0 1.5 2.0 2.5 3.00.0

0.2

0.4

0.6

0.8

1.0 (c)

Cou

t/Cin

Time (h)

Cr (Cin=60mg/L) Cu (Cin=60mg/L) Cd (Cin=45mg/L) Pb (Cin=30mg/L)

Fig. 3 e Effect of concentrations of heavy metals on the remova

concentration of Cr (VI): 20 mg/L, Cu (II): 20 mg/L, Cd (II): 15 mg

experimental time from 0.5 to 3 h), (b) initial concentration of C

20 mg/L (Inset: expanded chart of (b) at the experimental time fr

(II): 60 mg/L, Cd (II): 45 mg/L, and Pb (II): 30 mg/L, and (d) initial

75 mg/L, and Pb (II): 50 mg/L. Cout and Cin represented the concen

represent the standard deviation of the measurements.


Eichhornia crassipes, heavy metals were removed in the

order: Pb (II) > Zn (II) > Cd (II) > Cu (II) (Shama et al., 2010). The

solution pH is increased as the reaction proceeds, leading to a

decrease in Cr (VI) removal (Table 1). However, previous re-

searchers also found that the order was Cu (II) > Pb (II) > Zn

(II) > Cd (II) using goethite (McKenzie, 1980).

3.5. SEM characterization

Themorphology of EGDE-CS-NZVI beads is presented in Fig. 4.

It can be seen from Fig. 4(a) that the surface of these spherical

beads is loose and porous. The particular structure is favor-

able for mass transfer and energy flow between wastewaters

and the EGDE-CS-NZVI beads. There is a nucleus-shell struc-

ture inside of these beads in Fig. 4(b). The pore size of the

nucleus ranges from 19.2 to 138.6 mmwith an average aperture

size of around 58.6 mm. According to the previous results

(Wan-Ngah and Fatinathan, 2008), the nucleus of the beads is

macroporous and the pore sizes in EGDE-CS-NZVI beads are

heterogeneous. Other studies pointed out that the uniform

reaction between NaOH and acetic acid throughout the beads

led to the unique structure inside of the beads (Liu et al., 2010,

2012). The shell shows a tube structure linking the wastewater

with NZVI in the beads (Fig. 4(c)) and wastewaters can be

introduced into the beads through these tubes. It can be found

in Fig. 4(d) that NZVI particles are uniformly distributed in the

0 1 2 30.0

0.2

0.4

0.6

0.8

1.0

Cou

t/Cin

Time (h)

(b)

(d)

0.0 0.5 1.0 1.5 2.0 2.5 3.00.0

0.2

0.4

0.6

0.8

1.0

Cou

t/Cin

Time (h)

Cr(Cin=100mg/L) Cu(Cin=100mg/L) Cd(Cin=75mg/L) Pb(Cin=50mg/L)

l of heavy metals by EGDE-CS-NZVI beads PRBs: (a) initial

/L, and Pb (II): 10 mg/L (Inset: expanded chart of (a) at the

r (VI): 40 mg/L, Cu (II): 40 mg/L, Cd (II): 30 mg/L, and Pb (II):

om 0.5 to 3 h), (c) initial concentration of Cr (VI): 60 mg/L, Cu

concentration of Cr (VI): 100 mg/L, Cu (II): 100 mg/L, Cd (II):

tration of the effluent and influent, respectively. Error bars




Fig. 4 e Themorphology of EGDE-CS-NZVI beads was analyzed: (a) SEM image of the surface of EGDE-CS-NZVI beads, (b) SEM

image of the cross-section of EGDE-CS-NZVI beads, (c) higher magnification of SEM image of the edge of the cross-section, (d)

the distribution of NZVI particles in the EGDE-CS-NZVI beads.

25000

(b)


EGDE-CS-NZVI beads. It indicates that NZVI supported in

EGDE-CS beads can prevent the particles from aggregation.

Similar phenomena are also found in other NZVI systems,

such as kaolinite-supported NZVI, ECH-CS-NZVI beads (Liu

et al., 2012; Uzum et al., 2009).

0

5000

10000

15000

20000

1400 1200 1000 800 600 400 200 0

C/S

Binding Energy (eV)

(a)

Cu

CCr

CdPb

Fe

O

Fig. 5 e Typical wide scan XPS spectra for the EGDE-CS-

NZVI beads before and after heavy metals reduction: (a)

before heavy metals reduction and (b) after heavy metals

reduction. Initial concentration: 60 mg/L Cr (VI), 60 mg/L Cu

(II), 45 mg/L Cd (II), and 30 mg/L Pb (II); the concentration of

NZVI in CS-NZVI: 10.0 g/L; pH: 6.4; temperature: 20 �C.

3.6. XPS characterization

The results of XPS characterization were shown in Fig. 5 and

Fig. 6. It is clear that new peaks at the binding energy (BE) of

944 eV, 580 eV, 406 eV and 139 eV appeared after heavymetals

reduction. The presence of the bands were assigned to the

photoelectron peak of Cu, Cr, Cd and Pb, respectively, which

indicated the uptake of Cu, Cr, Cd and Pb on the surface of

EGDE-CS-NZVI beads.

Detailed XPS surveys on the region of Fe2p3/2, Cr2p3/2,

Cu2p3/2, Cd3d5/2 and Pb4f7/2 are presented in Fig. 6. Photo-

electron peaks at 711.8 and 725.0 eV (Fig. 6 (a)) correspond to

the binding energies of 2p3/2 of oxidized iron [Fe (III)]. The peak

at 706.5 eV assigned to Fe0 (Chatterjee et al., 2009) was not

observed in this study. It indicates that extensive oxidation of

iron occurs on the surface of NZVI and little Fe0 remains. The

photoelectron peak for Cr2p3/2 centers at 577.2 and 587.6 eV

(Fig. 6(b)) which have binding energies and line structures

similar to those of Cr (III) (Wan-Ngah et al., 2008). The XPS

Please cite this article in press as: Liu, T., et al., Enhanced chitosan beads-supported Fe0-nanoparticles for removal of heavymetals from electroplating wastewater in permeable reactive barriers, Water Research (2013), http://dx.doi.org/10.1016/j.watres.2013.09.006



1900

2000

2100

2200

2300

2400

2500

2600

727 723 719 715 711 707 703

C/S

Binding Energy (eV)

Fe2p3/2

Fe(III)

(a)Fe(III)

1350

1400

1450

1500

1550

1600

1650

1700

589 585 581 577 573 569

C/S

Binding Energy (eV)

Cr2p3/2

Cr(III)

(b)

Cr(III)

2600

2800

3000

3200

3400

957 953 949 945 941 937 933 929

C/S

Binding Energy (eV)

Cu2p3/2

Cu(II)

(c) Cu(0)

700

750

800

850

900

950

1000

419 415 411 407 403 399C

/S

Binding Energy (eV)

Cd3d5/2

Cd(0)

(d)

Cd(II)

450

470

490

510

530

550

570

590

150 146 142 138 134 130 126

C/S

Binding Energy (eV)

Pb4f7/2(e)

Pb(II)

Pb(0)

Fig. 6 e High-resolution XPS survey of (a) Fe2p3/2, (b) Cr2p3/2, (c) Cu2p3/2, (d) Cd3d5/2 and (e) Pb4f7/2 of EGDE-CS-NZVI-beads

PRBs after reacting with electroplating wastewater for 2 h. Initial concentration of Cr (VI): 100 mg/L, Cu (II): 100 mg/L, Cd (II):

75 mg/L, and Pb (II): 50 mg/L; the concentration of NZVI in CS-NZVI: 10.0 g/L; pH: 6.4; temperature: 20 �C.


results implied that the reduction of Cr (VI) to Cr (III) was

complete in less than 2 h.

The new peaks at a BE of 932.4 eV and 952.2 eV can be

attributed to the spin-orbit doublet of the Cu2p core level

transition (Mekki et al., 1997), which are assigned to Cu (0) and

Cu (II) (Fig. 6 (c)), respectively (Li and Bai, 2005). The main peak

was known as characteristics of Cu (0) (Fig. 6 (c)). Hence, it was

reasonably proposed that Cu (II) was removed predominantly

by reduction and the formation of Fe(III)eCu(II) co-

precipitated in this study. According to the previous study,

at pH > 6, Cu (II) species presenting in the solution were

mainly Cu(OH)þ and Cu(OH)2 (Nuhoglu and Oguz, 2003). At

pH < 5.7, Cu (II) removal by NZVI conformed to a chemically

reductive model, whilst at higher pH (>5.7) removal mecha-

nism of Cu (II) was neither by a reductive or adsorptive model

(Scott et al., 2011). Lai and Chen (2001) reported that Cu was


chemisorbed onto iron-coated sand. However, it is also re-

ported that the Cu adsorption on the iron-containing adsor-

bents was attributed to the formation of strong bonds

between Cu (II) and the iron (hydr)oxides (Qian et al., 2009).

Similarly, the Cd3d5/2 survey (Fig. 6(d)) presents a photo-

electron peak centering at 404.8 and 411.6 eV, which come

from Cd (II) and Cd (0), respectively (Li and Zhang, 2007). It is

also observed that the peak at 404.8 eV is stronger than that at

411.6 eV, which means that Cd (II) are mainly adsorbed on the

EGDE-CS-NZVI beads surface and a small portion of Cd (II) is

reduced to Cd (0). Fe(III)eCr(III) hydroxide can be used as an

efficient adsorbent material for Cd(II) removal from waste-

waters (Namasivayam and Ranganathan, 1995). In fact, the

presence of both cationic and anionic species, such as CrO42�,

CuClþ, CdClþ and PbðNO3Þþ, caused Cd (II) removal via pre-

cipitation of their minerals/salts (Genc-Fuhrman et al., 2008).




0

0.02

0.04

0.06

0.08

0.1

0.12

Cou

t/Cin

Cr Cu Cd Pb

Fig. 7 e Application of EGDE-CS-NZVI beads PRBs to

remove heavy metals from actual electroplating

wastewater. The concentration of NZVI in CS-NZVI: 10.0 g/

L; pH: 4.56; temperature: 20 �C. Cout and Cin represented the



measurements.


In the study, both sorption and reduction are in effect for the

removal of Cd (II). Shokes and Moller (1999) proposed that

cadmium was rapidly reduced and plated onto the iron sur-

face, which is consist with the result reported by other re-

searchers (Wilkin and McNeil, 2003). However, some

researchers reported that Cd (II) was adsorbed on NZVI sur-

face by electrostatic interaction and specific surface bonding

(Li and Zhang, 2007).

As shown in Fig. 6(e), the Pb4f7/2 has two peaks at 136.0 eV

and 138.4 eV, which can be contributed to Pb (0) and Pb (II)

(Ponder et al., 2000), respectively. That is, both metillic Pb (0)

and Pb (II) are present on the surface of EGDE-CS-NZVI beads.

Themain peak is known as characteristic of Pb (0). Hence, it is

reasonably proposed that both adsorption and predominant

reduction are in effect for the removal of Pb (II), conforming

the observation of previous studies (Lai and Chen, 2001;

Ponder et al., 2000).

3.7. Application of EGDE-CS-NZVI beads PRBs for heavymetals removal from actual electroplating wastewater

Before the remediation of actual electroplating wastewater,

the pH, dissolved oxygen (DO) and chemical oxygen demands

(COD) were 4.56, 4.37 mg/L and 1500 mg/L, respectively. The

concentrations of total Cr, Cu (II), Cd (II) and Pb (II) in actual

electroplating wastewater were 62.6, 55.8, 32.4 and 22.8 mg/L,

respectively (Table 2). After treatment by EGDE-CS-NZVI-

beads PRBs for 4 h, the pH, DO and COD was 7.56, 1.37 mg/L

and 32.4 mg/L, respectively. The pH of actual electroplating

wastewater increased, which is consistent with the result of

Table 1. The obviously reduction of COD means that the

degradable organic matter can be also removed by EGDE-CS-

NZVI-beads PRBs, which was confirmed by other researchers

using NZVI (Giasuddin et al., 2007; Zhang et al., 2011). The

removal rate of total Cr, Cu (II), Cd (II) and Pb (II) is 89.4%,

98.9%, 94.9% and 99.4%, respectively (Fig. 7), which is consis-

tent with the results shown in Fig. 3. The result revealed that

EGDE-CS-NZVI-beads PRBs had the capacity to remediate

actual electroplating wastewater and could become an effec-

tive and promising technology for remediation of heavy

metals.

However, microbial degradation may play an important

role in the in situ remediation of heavy metals. Some re-

searchers reported that a chlorophenol-degrading microor-

ganism entrapped in carrageenan-chitosan gels showed a

higher bioactivity than free microorganism (Wang and Qian,

1999). Chitosan hydrogel beads could serve as a carrier to

delivermacromolecules to the colon (Zhang et al., 2002). In situ

remediation combining ZVI and biodegradation has been

proposed for the treatment of mixed organic plumes (e.g.,

chlorinated solvents and petroleum hydrocarbons) (Ma and

Zhang, 2008). More attention should be paid to the effect of

Table 2e The concentration of each heavymetal in actualelectroplating wastewater.

Wastewater Total Cr Cu(II) Cd(II) Pb(II)

Concentration (mg/L) 62.6 55.8 32.4 22.8


microbial degradation on the removal of heavy metals by

EGDE-CS-NZVI beads in future study.

4. Conclusions

In this study, NZVI particles is more effective to remove heavy

metals from electroplating wastewater when enhanced chi-

tosan beads were introduced as a support material in PRBs.

Based on the results, the major finding are summarized as

follows:

1) Due to enhanced mechanical strength, the new and stable

EGDE-CS-NZVI beads are suitable as the reactive materials

in PRBs.

2) With an increase of pH, removal rate of Cr (VI) decreased

but the removal rates of Cu (II), Cd (II) and Pb (II) increased.

The solution pH increased as the reaction proceeded.

3) The removal rate of Cr (VI), Cu (II), Cd (II), and Pb (II)

decreased with an increase of the initial Cr (VI) concentra-

tion. At low concentrations (less than 40 mg/L), heavy

metals were removed in the order: Cd (II) > Cu (II) > Pb

(II) > Cr (VI). As the concentration increased, the removal

order was changed into Pb (II) > Cu (II) > Cd (II) > Cr (VI).

4) SEM images showed that with a loose and porous surface,

EGDE-CS-NZVI beads showed a nucleus-shell structure.

The pore size of the nucleus ranged from 19.2 to 138.6 mm

with an average aperture size of around 58.6 mm. The shell

showed a tube structure linking the outside environment

with NZVI particles and wastewater could be introduced

into the beads through these tubes.

5) The XPS results suggested that extensive oxidation of iron

happened on the surface of NZVI and little Fe0 was left. The

reduction of Cr (VI) to Cr (III) was complete in less than 2 h.

Cu (II) and Pb (II) were removed by predominant reduction

and the formation of Fe(III)-heavy metals co-precipitate.

However, Cd (II) was mainly adsorbed on the EGDE-CS-





NZVI beads surface and a small portion of Cd (II) was

reduced to Cd (0).

The result revealed that EGDE-CS-NZVI-beads PRBs had the

capacity to remediate actual electroplating wastewater and

could become an effective and promising technology for in situ

remediation of heavy metals.

Acknowledgments

The authors thank Zhigang Zhang, Qian Wang and Fei He for

their support with analyses. This work was financially sup-

ported by National Science & Technology Pillar Program

(2012BAC07B02), National Natural Science Foundation of

China (21307090), the University Science & Technology

Development Project of Tianjin (20110528), Program for New

Century Excellent Talents in University (NCET-10-0954), the

Natural Science Foundation of Tianjin (10SYSYJC27400),

Foundation of Tianjin Normal University (5RL109, 52XQ1104)

and Opening Fund of Tianjin Key Laboratory of Water Re-

sources and Environment (YF11700102).

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