Adsorption of Pb (II) from Aqueous Solutions by Pectic Acid

Microspheres

Fen Li

, Jianjun Li

1,3

, Xiaoyan Wen

, Xiaoyong Li

, Yanhong Bai

Yun Yang

and Zhao Xu

Department of Chemistry, Xi’an Jiaotong University, Xi’an 710061, China

Xi’an Modern Chemistry Research Institute, Xi’an 710065, China

Key Laboratory of Resource Biology and Biotechnology in Western China (Northwest University), Ministry of Education,

School of Life Science, Northwest University, Xi’an 710069, China

Keywords: Adsorption, Pectic Acid, Pb (II), Microspheres

Abstract: Pectin or modified pectin is used to remove the heavy metal ions in aqueous solution. The adsorption ability

of pectin microspheres (PMs) and pectic acid microspheres (PAMs) for Pb (II) in aqueous solution were

characterized by the parameters such as pH, initial concentration, and contact time for Pb (II) removal in this

work. The results showed that adsorption for 150 min at pH 5 was the optimal condition. The maximum

adsorption capacity of PMs and PAMs for Pb (II) was 127 mg·g

-1

and 325 mg·g

-1

, respectively. Five-cycle

reusability tests demonstrated microspheres could be repeatedly used. All the results confirmed that PAMs

which presented outstanding adsorption capability and reusability could be a good candidate for wastewater

purification.

1 INTRODUCTUION

Heavy metal pollution has drawn much attention

because of its high toxicity and nonbiodegrad ability

(Jorgetto et al., 2015). The heavy metal accumulated

in water would affect people’s health through various

ways to a certain extent. Researches showed that

excessive heavy metal ions which could damage the

human brain and nervous system are intangible risk

for human beings (Chojnacka, 2010). For these

reasons, it has always been an urgent task for

researchers engaged on environmental security to

seek more reasonable ways of treating water pollution.

The mainly methods of removing heavy metals

are chemical precipitation (España et al., 2006),

adsorption (Shariful et al., 2017), membrane filtration

(Mortaheb et al., 2010), ion-exchange (Fonseca et al.,

2005), electrodialysis (Mohammadi et al., 2005), and

so on. Compared with conventional methods,

bioadsorption (Chen et al., 2017) is recently

considered as the most advisable method for heavy

metal removal due to its efficiency, reproducibility,

and environmental friendliness. According to reports

(Celus et al., 2017), pectin is regarded as a suitable

candidate among the available bioadsorbents. In this

study, pectin and modified pectin were used to

remove the heavy metal in an aqueous solution.

Pectin substances belonging to the group of

natural biopolymers are the ionic plant

polysaccharides (Liu et al., 2003). Their capacity in

aqueous solutions was proved in numerous studies

mainly due to their unique properties such as

hydrophilicity, biodegradability, nontoxicity

(Serguschenko et al., 2007). But pectin had a low

adsorption capacity when directly used to remove

heavy metal ions because esterified residues were not

active. Thus, in our work pectin was modified to

improve the adsorption ability.

In this study, the work aims at investigating the

different adsorption ability of pectin, and pectic acid

(PA) which was prepared from pectin by pH-

modification. Batches of experiments were

performed to evaluate its adsorption capacities for Pb

(II) in either single or binary metal ion solutions at

various pH values, contact time, and initial

concentrations. The results showed that the

adsorption ability of PAMs is higher than that of PMs

and their high adsorption performance would provide

great potential for water treatment. The highlight of

this research is that PAMs was efﬁcient in removing

Pb (II) with 325 mg·g

-1

from aqueous solutions at pH

5; PAMs that have absorbed Pb (II) are readily

removed from aqueous solutions and can be reused;

Li, F., Li, J., Wen, X., Li, X., Bai, Y., Yang, Y. and Xu, Z.

Adsorption of Pb (II) from Aqueous Solutions by Pectic Acid Microspheres.

DOI: 10.5220/0008189203010305

In The Second International Conference on Mater ials Chemistry and Environmental Protection (MEEP 2018), pages 301-305

ISBN: 978-989-758-360-5

301

high selective for Pb (II) of PAMs was showed in

mixed aqueous solutions of Cd (II) and Pb (II).

2 METHODS AND MATERIALS

2.1 Materials

Citrus pectin (CAS: 9000-69-5) was purchased from

Sigma Biotechnology Co. (America). Pb(NO

)

CaCl

and CdCl

·2.5H

O were got from Xi’an

Chemical Reagent Factory. All other reagents were of

analytical grade. The water used to prepare the

solutions was deionized water.

2.2 Preparation of PA and PAMs

2.2.1 Preparation of PA

The PA was prepared by method as described (Ilse et

al., 2009). Briefly, 10g citrus pectin power was

dissolved in 500 ml 1.0 mol·L

-1

NaOH ethanol

solution on a magnetic stirrer for 5 h at 4 ℃. Placed

overnight, the solution was filtered and the residue

was dissolved into 50% ethanol (v/v) adding 3 mol·L

HCl until the pH=1.5. After 1.5 h, the solution was

filtered and the residue was dissolved in 250 ml 50%

ethanol (v/v) containing 1% HCl stirring at 25 ℃ for

0.5 h. The mixture was filtered and the resultant

composites were washed with 50% ethanol (v/v) with

three times. After freeze-dried, the PA was obtained.

The esterification degree of pectin and PA were

determined using titrimetric method (Afanas’Ev et al.,

1984) and the results were 47.90% and 0.90%,

respectively.

2.2.2 Preparation of PAMs and PMs

The PA solution was prepared by dissolving 0.3 g of

PA power in 10 mL of deionized water (3%, w/v).

Using syringe (1 mL, 0.45 #) added the pectin

solution to the calcium chloride solution (5%, w/v)

dropwise, the needle was about 5 cm from the liquid

level. After 20 min, PAMs were collected through a

membrane filter separation, and then washed

thoroughly by deionized water. PMs were prepared

using the same procedure as PAMs, excepting the

concentration of calcium chloride solution was used

as 10%.

2.3 Characterization of PA and PAMs

FTIR (Fourier Transform infrared) spectra of PA,

pectin and microspheres were obtained by an FTIR

spectrometer (Nicolet AVATAR 360, Thermo

Instrument Company, Madison, USA) at the wave

number range of 400-4000 cm

−1

. SEM (TM-1000

SEM, Hitachi, Japan) was used to observe the surface

microstructure and morphology of PAMs and PMs.

2.4 Adsorption Experiments of Pb (II)

2.4.1 Adsorption Experiments

The experiments were performed at pH (1, 2, 3, 4, 5,

6), contact time (10, 20, 30, 60, 90, 120, 150, 180,

210, and 240 min) and initial concentration of Pb (II)

(50, 100, 150, 200, 250, 300, 350, 400, 450, 500, 600,

700 mg·L

−1

). To test the selective adsorption, a total

of 50 mg of microspheres was added into 100 mL

mixed solution which contains Cd (II) and Pb (II)

with the initial concentration of 250 mg·L

−1

at initial

pH 5.0. The reusability of microspheres was

evaluated via sequential cycles of adsorption-

desorption in a binary ion mixture system of Cd (II)

and Pb (II). After adsorption for Cd (II) and Pb (II),

the microspheres were collected, washed with

deionized water and constantly stirred for 1 h in

0.002M Na

EDTA solution for desorption. Then, the

microspheres were filtered and washed thoroughly

until Cd (II) and Pb (II) concentration in the filtrate

was almost equal to zero. The collected microspheres

were further used in the next adsorption cycle. The

regeneration tests were conducted for five times

under the same conditions to evaluate the reusability

of microspheres.

2.4.2 Calculation of Adsorption Capacity

The concentration of metal ions was measured by a

flame atomic absorption spectrophotometer (AA1700,

FULI Instrument, China). The adsorption capacity (q

)

was calculated by the equation:

VCC

)(





(1)

Where q

(mg·g

−1

) is the adsorption capacity, C

(mg·L

−1

) and C

(mg·L

−1

) are respectively initial and

final concentrations of metal ions, respectively. V (L)

is the volume of the metal ion solution, and m (g) is

the mass of the dried adsorbent.

MEEP 2018 - The Second International Conference on Materials Chemistry and Environmental Protection

302

3 RESULTS AND DISSCUSION

3.1 Characterization of PA and PAMs

3.1.1 FTIR Analysis

To investigate the chemical structure of PA and PMs,

the results of FTIR are shown in Figure 1. The main

characteristic absorption bands of pectin were

summarized as follows: 3346 cm

-1

(-OH group), 1731

-1

(-C=O in free carboxylic acid groups), 1607

−1

(-C=O in non-free carboxyl group ) (Martinez et

al., 2012). The peak at 1607 cm

-1

of PA dispeared

demonstrating that the non-free carbonyl group in PA

decreased, and the peak of 1730 cm

-1

increased,

indicating that the free carboxyl group increased. For

PMs, the intensity at 1730 cm

-1

and 3327 cm

-1

became

weaker, compared with pectin spectrum. For PAMs

spectrum, new bands at 1416 cm

-1

appeared and 3229

-1

dropped off compared with PA spectrum,

indicating that pectin and PA had a cross-linking

reaction successfully with Ca (II).

Figure 1: FTIR spectra of pectin, PA, PMs, and PAMs.

3.1.2 SEM Observation

The images of PMs and PAMs at different

magnification were recorded via SEM in Figure 2, by

which the surface morphology and texture of each

sample was mapped out. The surface of PMs with

fewer folds exhibits some small cracks and there are

more uniform folds on the PAMs surface. The mean

diameters of two microspheres all were 2 mm and had

an integral surface, which could facilitate the

separation and recycling of samples.

3.2 Effect of pH on Adsorption

The initial pH of aqueous solutions is an important

parameter that greatly influences the adsorption

property of an adsorbent. The experiments on effect

of pH were performed at initial pH 1.0-6.0 in whcih

Pb (II) solution with initial concentration of 130

mg·L

−1

and adsorption time lasted 240 min. The

results are displayed in Figure 3. At pH 1.0, both of

PMs and PAMs have the lower adsorption rate; when

the pH increased from 2.0 to 6.0, the adsorption rate

of PMs increased while that of PAMs tends to a

plateau. At pH 6.0, the adsorption rate of PMs and

PAMs for Pb (II) respectively reached maximum

values, about 69% and 95%, respectively. That may

be because –COO groups on microspheres donated

their electron pairs to Pb (II) to form complex, when

the pH was low, the carboxyl group in pectin was

protonated and the complexation of Pb (II) with the

active group was reduced. The degree of protonation

decreased with the pH rising, and the number of

active group participating in the complexation

increased. There are more carboxyl groups binding

site with Pb (II) in PA compared with pectin, so the

adsorption capacity of PAMs is higher than PMs’s.

When the value of pH in the solution reached to 6.0,

Pb (II) have tended to precipitate. There would be less

amount of Pb (II) remained consequently showing a

high adsorption rate in the result. The initial pH of the

Pb (II) solution was close to pH 5.0, while the

adsorption rate of the microspheres at pH 4 was

almost equal to that of them at pH 5, so the

optimization of pH in equilibrium adsorption is 5.0.

Figure 2: SEM images of PMs (A×50 and B×1000) and

PAMs (C×50 and D×1000).

3.3 Effect of Contact Time on

Adsorption

The experiments on influence of contact time were

conducted with initial Pb (II) concentration of 130

mg·L

−1

at pH 5.0. Figure 4 shows the effect of contact

time on Pb (II) adsorption of two kinds of

microspheres. After 90 min, the amount of adsorption

of PMs and PAMs on Pb (II) were 74% and 96%,

Adsorption of Pb (II) from Aqueous Solutions by Pectic Acid Microspheres

303

respectively. Then, the adsorption capacities

increased slowly with the increase of contact time

until reaching adsorption equilibrium at 150 min. It

was a slow process in which the metal ion diffusion

into pores and the adsorption by interior surface while

almost all facial adsorption sites of microspheres

have been occupied. The maximum adsorption

capacity of PMs and PAMs was 95.74 mg·g

-1

and

123.84 mg·g

-1

at pH 5.0.

Figure 3. Effects of pH on adsorption.

Figure 4: Effects of contact time on adsorption.

3.4 Effect of Initial Concentration on

Adsorption

The experiments on impact of initial Pb (II)

concentration were carried out at pH 5.0 for 150 min.

The effects of the initial Pb (II) concentration on the

adsorption of the microspheres are shown in Figure 5.

For PAMs, the amount of the adsorbed ions increased

slowly until approached the plateau at C

= 600

mg·L

−1

. The maximum adsorption capacity of PAMs

were 325 mg·g

−1

. Obviously, it was about 2.5 times

as much as that of PMs (127 mg·g

−1

), which indicated

the ability of chelating with metal ions of PAMs was

significantly improved by modified within the

experimental.

Figure 5: Effects of initial Pb (II) concentration on

adsorption.

3.5 Selective Adsorption

The tests of selective adsorption were carried out in

a binary ion mixture system of Cd (II) and Pb (II) at

pH 5.0 and with different contact time. The results

of the selective adsorption of PMs and PAMs for Cd

(II) and Pb (II) are shown in Figure 6. The results

indicated that the adsorption capacity of PAMs for

Pb (II) was higher than that of Cd (II) in the binary

metal ion solution. Moreover, the selectivity of

PAMs for Pb (II) is superior to PMs.

3.6 Desorption and Regeneration

The adsorption-desorption tests were repeated five

times in a binary ion mixture system. The results are

shown in Figure 7. After the 5th cycle, the adsorption

capacity of the PMs and PAMs for Pb (II) dropped to

15.66% and 9.64%, respectively, and remained

constant almost after the second cycle. However, the

adsorption capacities of PAMs for Pb (II) were even

143.47 mg·g

-1

with the existence of Cd (II). PAMs’s

adsorption capacities was about 2.2 times that of

PMs’s at the 5th recycle. These results indicated that

PAMs were of desirable reusability and stable

chemical property.

Figure 6: Effects of contact time on adsorption for Cd (II)

and Pb (II).

MEEP 2018 - The Second International Conference on Materials Chemistry and Environmental Protection

304

Figure 7: Results of five consecutive adsorption-desorption

for the reuse of microspheres for Pb (II) adsorption.

4 CONCLUSION

In this work, PMs and PAMs were successfully

fabricated through crosslinking with calcium ions.

The maximum adsorption capacity for Pb (II) of

PAMs was about 2.6 times of PMs which implied that

the adsorption ability of PAMs greatly increased.

And the selective adsorption capacity for Pb (II) of

PAMs was better than that of PMs. Moreover, the

result of regeneration experiments showed that the

removal efficiency for Pb (II) of PAMs was more than

54% after five adsorption-desorption cycles in a

binary ion mixture system. All the results above

implied that the newly-prepared PAMs might be the

promising adsorbent for Pb (II) in aqueous solutions.

ACKNOWLEDGEMENTS

This work was supported by Scientific Research

Foundation for Returned Scholars (Ministry of

Education of China, 201503), Opening Foundation of

Key Laboratory of Resource Biology and

Biotechnology in Western China (Northwest

University, Ministry of Education),Natural Science

Basic Research Plan in Shaanxi Province of China

(2017JM2016) and National Natural Science

Foundation of China (81673115).

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