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공학석사 학위논문

Assessment of the Adsorption

Characteristics of Cadmium and

Arsenic on Modified

Paper Mill Sludge

개질된 제지슬러지의 카드뮴 및 비소

흡착특성 평가

2014년 8월

서울대학교 대학원

건 설 환 경 공 학 부

백 종 찬

Assessment of the Adsorption

Characteristics of Cadmium and

Arsenic on Modified

Paper Mill Sludge

지도 교수 박 준 범

이 논문을 공학석사 학위논문으로 제출함

2014년 8월

서울대학교 대학원

건설환경공학부

백 종 찬

백종찬의 석사 학위논문을 인준함

2014년 8월

위 원 장 김 명 모 (인)

부위원장 박 준 범 (인)

위 원 정 충 기 (인)

iii

i

Abstract

Assessment of the Adsorption Characteristics of

Cadmium and Arsenic

on Modified Paper Mill Sludge

Baek, Jongchan

Department of Civil and Environmental Engineering

The Graduate School

Seoul National University

The purpose of this study is to promote utilization of paper mill

sludge as an adsorbent for stabilizing heavy metals in contaminated water by

measuring the adsorption capacity of paper mill sludge for cadmium and

arsenic. To measure adsorption capacity of paper mill sludge, sorption

isotherm experiments were analyzed by Langmuir and Freundlich isotherm

models. Also, two methods of chemical modifications were applied to

improve the adsorption capacities of paper-mill-sludge: the first method used

sodium hydroxide (NaOH), called PMS-1, and the second method used the

NaOH and tartaric acid (C4H6O6) together, called PMS-2. For Cd adsorption,

PMS-1 presented the increase of reactivity while PMS-2 presented the decline

of reactivity compared to that of untreated paper-mill-sludge. In case of As

adsorption, both PMS-1 and PMS-2 showed the decrease of adsorption

capacities. FTIR, XRF and zeta-potential experiment were performed to find

out a reason about difference of adsorption characteristics between original

and modified paper mill sludge. Zeta-potential of paper mill sludge was

ii

changed to more negative values during chemical modification process due to

the hydroxyl group in NaOH and the carboxyl group in C4H6O6, respectively.

Therefore, we may conclude that the chemical treatment process increases

adsorption capacity of paper mill sludge for cation heavy metals such as Cd

but not for As. Also, C4H6O6 can reduce amount of CaO(calcium oxide) which

can remove Cd by releasing OH- (hydroxide) and amine group which is

known as a chelating agent in paper mill sludge. In case of PMS-2, final pH

was decreased. This variation brings about competitive effect of cation. So, it

decreases adsorption capacity for heavy metals. In these reasons, in case of

ground water or Leachate contaminated with cation heavy metal such as Cd,

NaOH treatment is efficient. Inversely, when ground water was contaminated

with anionic heavy metals such as As, using untreated paper mill sludge is

better.

Keywords: Paper Mill Sludge, Sorption isotherm experiments, Zeta-

potential variations, Cadmium, Arsenic, Chemical treatment, etc.

Student Number: 2012-23252

iii

Contents

Chapter 1 Introduction........................................................... 1

1.1 Background .......................................................................... 1

1.2 Objectives and scopes .......................................................... 2

Chapter 2 Materials and Methods .......................................... 4

2.1 Materials .............................................................................. 4

2.1.1 Basic properties of paper mill sludge .................................... 4

2.1.2 Heavy metal contents analysis of paper mill sldge ................ 7

2.2 Methods ............................................................................... 8

2.2.1 Chemical treatment ......................................................... 8

2.2.2 Leaching experiments ..................................................... 9

2.2.3 Sorption isotherm experiments ........................................ 9

2.2.4 Zeta-potential variations ................................................ 10

2.3 Sorption isotherm models ................................................... 11

Chapter 3 Results and Discussion ........................................ 13

3.1 Leaching analysis of paper mill sludge in various pH ......... 13

3.2 Sorption isotherm for cadmium on original & modified paper

mill sludge ................................................................................... 15

3.3 Sorption isotherm for arsenic[Ⅴ] on original & modified

paper mill sludge ......................................................................... 18

iv

3.4 Difference of adsorption characteristics between original and

modified paper mill sludge .......................................................... 20

3.4.1 Zeta-potential variations ................................................ 20

3.4.1 Chemical composition of modified paper mill sludge .... 23

3.4.2 Functional group of modified paper mill sludge ............ 26

3.4.3 Variations of pH after reaction ....................................... 29

Chapter 4 Conclusions......................................................... 31

Bibliography ....................................................................... 34

v

List of Tables

Table 2.1 Chemical composition of paper mill sludge .................................. 5

Table 2.2 Basic properties of paper mill sludge ............................................ 6

Table 2.3 Total concentration of heavy metals extracted from paper mill

sludge .......................................................................................... 7

Table 3.4 Constants of Langmuir and Freundlich sorption isotherm for Cd at

pH 4 ........................................................................................... 15

Table 3.5 Constants of Langmuir and Freundlich sorption isotherm for

As[Ⅴ] ]; (a) pH 4, (b) pH 8 ........................................................ 18

Table 3.6 Chemical composition of original& modified paper mill sludge;

(a) Paper mill sludge (b) PMS-1 (c) PMS-2 ................................ 23

vi

List of Figures

Figure 2.1 Paper mill sludge ........................................................................... 4

Figure 2.2 Zeta potential .............................................................................. 11

Figure 3.3 Leaching result of paper mill sludge from final pH 2 to 11 ........... 13

Figure 3.4 Sorption isotherm for Cd on original & modified paper mill sludge

at pH 4 ....................................................................................... 15

Figure 3.5 Sorption isotherm for Cd on original & modified paper mill sludge

in various pH conditions... .......................................................... 16

Figure 3.6 Sorption isotherm for As[Ⅴ] on original& modified paper mill

sludge; (a) pH 4, (b) pH 8 ........................................................... 18

Figure 3.7 Zeta-potential variations of original& modified paper mill sludge

from pH 2 to 12; (a) Paper mill sludge (b) PMS-1 (c) PMS-2 ...... 21

Figure 3.8 FTIR spectrum of original & modified paper mill sludge; (a) Paper

mill sludge (b) PMS-1 (c) PMS-2 ............................................... 27

Figure 3.9 pH of Cd solution variations after reaction; (a) Paper mill sludge

(b) PMS-1 (c) PMS-2 ................................................................. 29

1

Chapter 1 Introduction

1.1 Background

Nowadays heavy metals are among the most important pollutants in

source and treated water, and are becoming a severe public health problem.

Industrial and municipal waste waters frequently contain metal ions. These

metal ions can be harmful to aquatic life and water contaminated by toxic

metal ions remains a serious public health problem for human health

(Demirbas, 2007). Heavy metals removal from aqueous solutions has been

traditionally carried out by adsorption. This is because, heavy metal ions are

stable and persistent environmental contaminants since they cannot be

degraded and destroyed.

Heavy metal sorption used waste material is relatively new process

that has proven very promising in the removal of contaminants from

contaminated water. Adsorption materials derived from low cost waste

materials can be used for the effective removal and recovery of heavy metal

ions from contaminated water. Also, to clean up the contaminated site more

friendly environmental, EPA highlight materials should be recycled whenever

possible.

The purpose of my study is to promote utilization of paper mill

sludge as adsorbent to stabilize heavy metal in contaminated water. Paper mill

sludge is generated in enormous amount annually from paper manufacturing

2

process and this is considered as waste material. In recent years, the

management of paper mill sludge has become a significant issue in

environmental engineering due to generating enormous quantities and the

associated disposal costs and constrains. It was produced around 3 hundred

thousand ton per a year (Lim et al., 2011). Most of paper mill sludge is

disposed at landfill site. So, many studies about recycling paper sludge were

conducted. For example, it use as fertilizer (Song et al., 2010) and addition

agent of cement for increasing strength (Ju et al., 2003). Paper mill sludge

used as adsorbent can be helpful environmental friendly.

1.2 Objectives and scopes

The purpose of this study is to promote utilization of paper mill

sludge as an adsorbent in purify method such as Permeable Reactive Barriers

(PRB) for stabilizing heavy metals in contaminated water by measuring the

adsorption capacity of modified paper mill sludge for cadmium and arsenic.

By using paper mill sludge as adsorbent, it can reduce ground water

remediation cost and disposal cost of waste materials.

To identify toxic element leach out from sludge, leaching

experiments were performed. Also, Sorption isotherm experiments for

cadmium and arsenic were performed to measure adsorption capacity of paper

mill sludge. The results of sorption isotherm experiments were analyzed by

Langmuir and Freundlich isotherm.

3

Also, two methods of chemical treatment were applied to improve

the adsorption capacities of paper-mill-sludge: the first method used sodium

hydroxide (NaOH), called PMS-1, and the second method used the NaOH and

tartaric acid (C4H6O6) together, called PMS-2.

Finally, FTIR, XRF and zeta-potential experiment were performed to

find out a reason about difference of adsorption characteristics on modified

sludge.

4

Chapter 2 Materials and Methods

2.1 Materials

2.1.1 Basic properties of paper mill sludge

The paper mill sludge used in this study produced from the

Samwha paper company in South Korea. Fig. 2.1 shows paper mill sludge.

Fig. 2.1 Paper mill sludge

Prior to proceeding experiment, break paper mill sludge by using

hammer and use paper mill sludge passing the No. 8 sieve to reduce negative

effect by non-homogeneity.

5

Table 2.1 Chemical composition of paper mill sludge

The chemical composition of the paper mill sludge was analyzed by

X-ray fluorescence spectrometer (XRF-1700, Shimadzu). Element of CHO

is pulp and organic contents. The sum of contents of CaO and MgO is about

26%, which could lead pH increase (Weng and Huang., 1994). So, paper

mill sludge has some alkalinity.

6

Table 2.2 Basic properties of paper mill sludge

Basic properties of paper mill sludge such as PH, CEC (cation

exchange capacity), organic content and etc. were summarized in Table 2.

The pH of the paper mill sludge was measured by pH meter (Orion 3-star,

Thermo Scientific, US) by mixing 10g of the dried paper mill sludge and

25mL of DI water (Deionize water) for 1h. The CEC of paper mill sludge

was measured by ammonium acetate method. The organic content of paper

mill sludge was measured by Walkley black method. In this table, we can

know that paper mill sludge has higher cation exchange capacity

(17.86cmol/kg) than steel making slag (13.3cmol/kg; Kim et al., 2011). So,

we can presume that paper mill sludge can adsorb heavy metal by ion

exchange.

7

2.1.2 Heavy metal contents analysis of paper mill sludge

Table 3 is Total concentration of Heavy metal from Paper Mill

Sludge by using Korean Standard Method for Soil Analysis. The total

concentration of heavy metal was below than worrisome level of soil

contamination in Korea.

Table 2.3 Total concentration of heavy metals extracted from paper mill

sludge

8

2.2 Methods

2.2.1 Chemical treatment

In my study, Chemical treatment was performed to enhance

adsorption capacity for heavy metal. Many researchers reported that

chemical such as Sodium hydroxide (NaOH) or Tartaric acid (C4H6O6) can

remove impurities and smoothed the surface of adsorbent such as rice husk

and sawdust. This variation brings about increasing the number of active

sites. So, chemical treatment enhances adsorption capacity for heavy metals

(Lee et al., 2009, Memona et al., 2007, Sciban et al.,2006, Wong et al., 2003).

Two methods of chemical modifications were applied to improve

the adsorption capacities of paper-mill-sludge. The first method used sodium

hydroxide (NaOH), called PMS-1. Chemical treatment agent was prepared

by mixing unit gram of Dry paper mill sludge with 10ml of 1M Sodium

hydroxide (NaOH). And then stir for 2hrs and the treated sludge was washed

with DI water until neutral. Finally, it dried at 80℃ overnight. Drying at

80℃ was chosen because high temperature might cause a decrease of the

number of cellulose based OH- groups on the paper mill sludge (Sciban et

al.,2006).

The second method used the NaOH and tartaric acid (C4H6O6)

together, called PMS-2. Chemical treatment agent was prepared by mixing

unit gram of dry paper mill sludge with 20ml of 0.1 M NaOH and doing

same process as first method. And then modified agent was mixing 7 ml of

9

1.2 M tartaric acid (C4H6O6). And then stir for 2hrs and the treated sludge

was washed with DI water until neutral. Finally, it dried at 80℃ overnight.

2.2.2 Leaching experiments

Paper mill sludge contains some heavy metals such as cadmium,

copper, lead and arsenic. Leaching tests were performed to identify heavy

metals leach out from paper mill sludge.

At first, 2 grams of paper mill sludge and 90ml of DI water were

placed in plastic beaker. After that, Hydrochloride (HCL) or Sodium

hydroxide (NaOH) was added to solution to variation with final pH from 2 to

11. And then, beakers were shaken on table shaker for 24hrs. The

concentration of heavy metals was analyzed by Inductively Coupled Plasma

- Atomic Emission Spectrometer (ICP-AES, Shimadzu, Japan) with Hydride

generator (HG, Shimadzu, Japan) or Ultrasonic aerosol generator (UAG,

Shimadzu, Japan).

2.2.3 Sorption isotherm experiments

Unit gram of paper mill sludge and 100ml of Cadmium (Cd)

solution or arsenic[∨] (As[∨]) solution were placed in plastic beaker. HCl

add to solution to variation with initial pH. And then, beakers were shaken

10

on table shaker for 24hrs. Cd adsorption test conducted at pH 2, 4,

8condition and As[∨] adsorption test conducted at pH 4 and 8condition.

Initial concentration of Cd solution is from 80ppm to1800ppm. Initial

concentration of As[∨] solution is from 10ppm to 240ppm. The

concentration of contaminants was analyzed by Atomic absorption System

(AAS, nova 300, Analytik Jena AG). Results of sorption isotherm

experiments were analyzed by Langmuir and Freundlich isotherm model. Cd

and As[∨] solution were prepared by adding appropriate amounts of

Cadmium chloride(CdCl2∙2.5H2O) or Sodium Arsenate(Na2HAsO4∙7H2O)

into deionized (DI) water from Milli-Q apparatus (Millipore, USA)

respectively. Hydrochloride (HCL) was used for pH adjustment.

2.2.4 Zeta-potential variations

Zeta potential (fig. 2.2) are performed to examine charge on s

urface of adsorbent. This experiment was performed to see the adsorpt

ion characteristics on untreated & treated paper mill sludge. 0.1g of p

aper mill sludge (<50㎛) and 10ml of DI water placed in standard vial.

After that, add 0.1M HCl or NaOH solution to control pH. Zeta poten

tial was analyzed by Nano-ZS60 (Malvern Instruments, UK).

11

Fig . 2.2 Zeta potential

2.3 Sorption isotherm models

Results of sorption isotherm experiments were analyzed by

Langmuir and Freundlich isotherm model. The Langmuir and Freundlich

models are the ones most frequently employed to describe experimental data

of adsorption isotherms.

The Langmuir sorption isotherm was developed with the concept

that a solid surface possesses a finite number of sorption sites. When all the

sorption sites are filled the surface will no longer sorb solute from solution.

The form of the Langmuir sorption isotherm is following equation:

1

es

e

CC

C

12

where, α is adsorption constant related to the binding energy

(L/mg), β is the maximum amount of solute that can be absorbed by the

solid (mg/kg), Ce is final heavy metal concentration.

The Freundlich isotherm was developed with the concept that a

solid surface possesses a infinite number of sorption sites. The form of the

Freundlich sorption isotherm is following equation:

N

s f eC K C

where, Kf and N is Freundlich constants related to adsorption

capacity. One of the major disadvantages of the Fruendlich model is that it

can’t predict an maximum adsorption capacity. The single Kf term implies

that the energy of adsorption on a homogeneous surface is independent of

surface coverage (Fetter, 1999).

13

Chapter 3 Results and Discussion

3.1 Leaching analysis of paper mill sludge in various pH

Standard of groundwater quality

Standard of groundwater quality

14

Fig. 3.3 Leaching result of paper mill sludge from final pH 2 to 11

In the result of table 2.3, the total concentration of heavy metal was

below than the regulation level in Korea. However, some heavy metals such

as Cu, Pb, As, Zn is little high concentration. So, this study was performed

the leaching tests to identify toxic element leach out from the paper mill

sludge. Figure 3.3 shows leaching test result.

Cu and Zn leach out from paper mill sludge at alkali condition and

acid condition respectively. However, the concentration of Cu, Zn was

below than regulation level of water for living in Korea. Also, concentration

of As was below than regulation level. Cd, Pb didn’t leach out from the

paper mill sludge. Therefore, secondary contamination is not expected when

paper mill sludge is used as adsorbent for heavy metal in contaminated water.

Standard of groundwater quality

Standard of groundwater quality

15

3.2 Sorption isotherm for cadmium on original &

modified paper mill sludge

The result for cadmium sorption isotherm experiment of original&

modified paper mill sludge is shown in Figure 3.4. Table 3.4 shows

Langmuir and Freundlich isotherm parameters. The sorption result was

analyzed by Langmuir and Freundlich model.

Fig. 3.4 Sorption isotherm for Cd on original & modified paper mill sludge

at pH 4

Table 3.4 Constants of Langmuir and Freundlich sorption isotherm for Cd at

pH 4

16

Results of adsorption isotherms were more adequately described by

Langmuir model than Freundlich model. The maximum capacity (β) of

paper mill sludge on Cd is 112.52mg/kg at pH 4. Therefore, paper mill

sludge has high potential to recycling as adsorbent because the maximum

capacity of paper mill sludge is higher than steel making slag (29.2mg/g) as

good adsorbent for heavy metals (Kim et al., 2011).

PMS-1(paper mill sludge treated with NaOH) presented the

increase reactivity. Inversely, PMS-2 (paper mill sludge treated with C4H6O6)

presented the decline of reactivity compared to that of original paper mill

sludge. Maximum adsorption capacity of PMS-1 is improved about 80%

than original sludge.

(a) Paper mill sludge

17

(b) PMS-1

(c) PMS-2

Fig. 3.5 Sorption isotherm for Cd on original & modified paper mill sludge

in various pH conditions

Fig. 3.5 shows sorption isotherm for Cd on original & modified

paper mill sludge in various pH conditions. This figures show that sorption

characteristics in pH 4 and 6 are similar. In other words, sorption ability of

18

paper sludge is good at pH 4 condition such as landfill leachate. However,

sorption capacity is sharply decreases at strong acid condition such as acid

mine drainage.

3.3 Sorption isotherm for arsenic[Ⅴ] on original &

modified paper mill sludge

Figure 3.6 illustrates sorption isotherm for arsenic[Ⅴ] on original

& modified paper mill sludge and Table 3.5 shows Langmuir and Freundlich

isotherm parameters. The sorption result was analyzed by Langmuir and

Freundlich model.

(a) pH 4

19

(b) pH 8

Fig. 3.6 Sorption isotherm for As[Ⅴ] on original& modified paper mill

sludge; (a) pH 4, (b) pH 8

Table 3.5 Constants of Langmuir and Freundlich sorption isotherm for

As[Ⅴ] ]; (a) pH 4, (b) pH 8

(a) pH 4

(b) pH 8

20

Results of adsorption isotherms were more adequately described by

Langmuir model than Freundlich model. The maximum capacity (β) of paper

mill sludge on As[Ⅴ] is 5.98mg/kg at pH 4 and 4.82mg/kg at pH 8.

Adsorption capacity at pH 8 little decrease than pH 4 condition. Also, in case

of As[Ⅴ] adsorption, both PMS-1 and PMS-2 showed the decrease of

adsorption capacity.

3.4 Difference of adsorption characteristics between

original and modified paper mill sludge

3.4.1 Zeta-potential variations

Figure 3.7 illustrates zeta potential variation of the Original &

modified paper mill sludge from pH 2 to 12. Paper mill sludge has positive

zeta potential in the acidic region (pH<5.4) ranging from +0 to 12 mV.

Positive zeta potential values indicate that positively charged surfaces are

dominant on the material. In this positive region, paper sludge has advantage

of adsorption efficiency for Arsenic.

Beyond pH 5.4 increasing the pH resulted in the gradual decrease

of the zeta potential until the isoelectronic point. Further increase in pH

beyond the IEP resulted in the decrease of the zeta potential until lowest

value of -18mV was reached around pH 12. Negative values of zeta potential

suggest that the surface of the material has a net negative charge. In this

negative region, paper sludge has advantage of adsorption efficiency for

Cadmium (Bismarck et al., 2000).

21

Paper mill sludge treated with NaOH (PMS-1) has lower negative

zeta-potential than untreated sludge. This is because zeta-potential was

decreased by Hydroxyl group in NaOH(Park et al., 2007). So, we can

presume that it increases adsorption capacity for heavy metal. However, It is

expected to decrease adsorption capacity for As.

Zeta potential of paper mill sludge treated with C4H6O6 (PMS-2) is

similar with untreated sludge. This is because Harry et al. (2006) reported

that deprotonation of carboxyl group in tartaric acid mainly occurred in the

range from pH 2 to 6. However, tartaric acid is weak acid, so it shows very

little difference between original sludge and acid treated sludge.

(a) Paper Mill Sludge

22

(b) PMS-1

(c) PMS-2

Fig. 3.7 Zeta-potential variations of original& modified paper mill sludge

from pH 2 to 12;

(a) Paper mill sludge (b) PMS-1 (c) PMS-2

23

3.4.2 Chemical composition of modified paper mill

sludge

Table 3.6 shows chemical composition of original and modified

paper mill sludge was analyzed by X-ray fluorescence spectrometer (XRF-

1700, Shimadzu).

Table 3.6 Chemical composition of original& modified paper mill sludge; (a)

Paper mill sludge (b) PMS-1 (c) PMS-2

(a) Paper mill sludge

24

(b) PMS-1

(c) PMS-2

25

This table shows that PMS-1 which is paper mill sludge treated

with NaOH has similar chemical composition with original paper mill sludge.

However, PMS-2 which is paper mill sludge treated with acid has

smaller amount of CaO than untreated sludge.

2 2CaO + H O Ca(OH) (1)

2+ -

2Ca(OH) Ca + 2OH (2)

2+ -

2Ca + 2OH Cd(OH) (3)

If CaO contact with water, it can release OH-(hydroxide). After that,

OH- can remove Cd by precipitate (Park, 2013). However, acid treatment

can reduce CaO. In this reason, acid treated paper sludge shows lower

adsorption capacity than untreated sludge.

26

3.4.3 Functional group of modified paper mill sludge

The paper mill sludge samples were characterized by Fourier

Transformed Infrared (FTIR) spectroscopy. FTIR can identify the major

functional groups in samples. The FTIR spectra of original and modified

paper mill sludge are presented in figure 3.8.

As illustrated in fig 3.8 (a), (b), (c), broad band at 3550 – 3100cm-1

is observed which corresponds to the H-boned OH groups of alcohols,

phenols and organic acids, as well as the H bonded N-H groups.

The maximum adsorption of original paper mill sludge (fig 3.8 (a))

and PMS-1 (fig 3.8 (b)) at 1400 – 1500cm-1

can be assigned to amine group

and calcium carbonate. Amine group is known as a chelating agent which is

can bond to metal ion such as cadmium (Fetter, 199). Also, calcium

carbonate would play an important role in the removal of cadmium. It has

been reported that cadmium can be co-precipitated by calcium carbonate

(Park, 2013).

However, we cannot show amine group and calcium carbonate at

PMS-2 (fig 3.8 (c)). We can presume that acid can reduce amount of amine

group and calcium carbonate. In these reasons, PMS-2 shows lower

adsorption capacity.

27

(a) Paper mill sludge

(b) PMS-1

69

7.0

4

75

2.8

3

85

3.9

88

73

.68

91

3.1

91

00

7.5

31

03

1.4

0

10

94

.69

11

59

.03

14

20

.42

17

29

.08

17

90

.442

84

9.1

2

29

16

.97

33

39

.06

36

19

.33

36

93

.51

*p

64

66

68

70

72

74

76

78

80

82

84

86

88

90

92

94

96

98

100

%T

1000 1500 2000 2500 3000 3500

W avenumbers (cm-1)

69

7.3

3

75

4.2

4

85

4.0

08

73

.43

91

3.2

21

00

7.8

91

03

1.8

6

10

84

.45

14

21

.00

17

30

.76

17

92

.60

28

49

.13

29

16

.85

33

39

.39

36

19

.87

36

93

.01

*NaOH

72

74

76

78

80

82

84

86

88

90

92

94

96

98

100

%T

1000 1500 2000 2500 3000 3500

W avenumbers (cm-1)

28

(c) PMS-2

Fig. 3.8 FTIR spectrum of original & modified paper mill sludge;

(a) Paper mill sludge (b) PMS-1 (c) PMS-2

69

7.4

3

81

5.0

48

47

.97

91

2.6

1

10

08

.44

10

30

.68

10

60

.20

11

46

.87

12

37

.54

12

82

.50

13

31

.18

13

83

.78

14

92

.32

15

79

.94

17

29

.68

28

48

.90

29

16

.76

32

73

.87

34

11

.143

61

9.1

43

69

2.8

4

*A c id

76

78

80

82

84

86

88

90

92

94

96

98

100

%T

1000 1500 2000 2500 3000 3500

W avenumbers (cm-1)

29

3.4.4 Variations of pH after reaction

Figure 3.9 illustrates pH of Cd solution variations after adsorption

experiments. Acid contaminated water can be neutralized by using paper

mill sludge as adsorbent. This is because paper mill sludge has CaO and

MgO about 26% which could lead pH increase.

However, In case of PMS-2, final pH was decreased. When final

pH decreased, it increases competitive effect of cation such as metal ions and

hydrogen ions in contaminated water. This variation brings about decreasing

adsorption capacity for heavy metals.

(a) Paper mill sludge

30

(b) PMS-1

(c) PMS-2

Fig. 3.9 pH of Cd solution variations after reaction;

(a) Paper mill sludge (b) PMS-1 (c) PMS-2

31

Chapter 4 Conclusions

In this study, adsorption capacity of paper mill sludge on cadmium

and arsenic[Ⅴ] is assessed to utilizing paper mill sludge as an adsorbent for

stabilizing heavy metals in contaminated water.

Physical and chemical properties of paper mill sludge were

measured. And then, leaching tests were performed to identify toxic element

which occurs secondary contamination for ground water leach out from the

paper mill sludge.

Also, this study was applied chemical treatment for paper mill

sludge to improve adsorption capacity for heavy metals. Based on the results

and analysis, the following conclusion is determined:

1. In the leaching test results, the concentration of heavy metals in

paper mill sludge was below than regulation level of water for living in

Korea. Therefore, there is no possibility of secondary contamination when

paper mill sludge is used as adsorbent.

2. Paper mill sludge has high potential to recycling as adsorbent

because the maximum capacity of paper mill sludge (112.52mg/kg) on Cd is

higher than steel making slag (29.2mg/g) as good adsorbent for heavy metals

(Kim et al., 2011).

32

3. Sorption characteristics of paper mill sludge on Cd at pH 4 and 6

are similar. In other words, Sorption ability of paper mill sludge is good at

pH 4 condition such as landfill leachate. However, sorption capacity is

decreased at strong acid condition such as acid mine drainage.

4. For Cd adsorption, PMS-1(paper mill sludge treated with NaOH)

increases adsorption capacity of Cd. However, PMS-2 (paper mill sludge

treated with NaOH & C4H6O6) presented the decline of reactivity compared

to that of untreated paper-mill-sludge. In case of As[Ⅴ] adsorption, both

PMS-1 and PMS-2 showed the decrease of adsorption capacity.

5. There are differences of adsorption characteristics between

original and modified paper mill sludge. Zeta-potential of paper mill sludge

was changed to more negative values during chemical modification process

due to the hydroxyl group in NaOH and the carboxyl group in C4H6O6,

respectively. Therefore, we may conclude that the chemical treatment

process increases adsorption capacity of paper mill sludge for cation heavy

metals such as Cd but not for As.

6. C4H6O6 can reduce amount of CaO (calcium oxide) which can

remove Cd by releasing OH- (hydroxide) in paper mill sludge. Also, in the

results of FTIR spectra, amine group which is known as a chelating agent

was disappeared at PMS-2. We can presume that acid can reduce amount of

amine group and calcium carbonate. In case of PMS-2, final pH was

33

decreased. This variation brings about competitive effect of cation such as

metal ions and hydrogen ions in contaminated water. So, it decreases

adsorption capacity for heavy metals.

7. Based on these results, in case of ground water or Leachate

contaminated with cation heavy metal such as Cd, NaOH treatment for paper

mill sludge is efficient. Inversely, when ground water was contaminated with

anionic heavy metals such as As, using original paper mill sludge is better.

34

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37

초 록

국내 종이류 생산량은 약 1055만톤을 기록하며 세계 8위의

생산국으로서 그 입지를 다지는 반면 이 과정에서 매년 30만톤

가량의 산업폐기물인 제지슬러지가 발생한다(Lim et al., 2011).

산업폐기물인 제지슬러지는 주로 매립에 의해 처리되고 있으며,

현재 이러한 제지슬러지의 처리비용 절감과 처리공정 개선을 위한

많은 연구가 진행 중이다. 국내의 제지슬러지 재활용에 관한

연구에는 대표적으로 퇴비로서의 이용(Song et al., 2010), 시멘트의

강도 개선을 위한 혼화재로서의 사용(Ju et al., 2003)등이 있다.

이외에, 국외의 연구사례로 제지슬러지와 중금속의 반응성을

연구한 Calace et al.,(2002)은 제지슬러지가 지하수 내의 중금속

흡착에 효과가 있으며, 이는 pH와 고액비에 영향을 받는다고

보고하였다. Battaglia et al.,(2003)는 토양에 제지슬러지를 혼합한 경우,

보통 토양보다 Cd과 Pb등의 중금속 흡착능이 증가한다고

보고하였다.

이러한 국외의 연구사례에 기초하여, 본 연구에서는 산업폐기물인

제지슬러지를 재활용하는 방안 중의 하나로, 중금속 등으로 오염된

지하수를 정화시키는 PRB(Permeable Reactive Barriers)공법의

흡착제로서의 사용 가능성을 평가한다. 우선, 국내에서 생산되는

38

제지슬러지가 토양오염을 유발하는 폐기물인지 여부를 판단하기

위해 전함량분석을 수행하였으며, 중금속으로 오염된 지하수 정화를

위한 흡착제로 사용 시, 지하수내의 이차오염 발생 여부를 파악하기

위해 용출실험을 추가로 진행하였다. 전함량 분석과 용출실험 결과,

용출된 유해 중금속들의 농도는 모두 기준치 미만으로,

제지슬러지를 오염 지하수정화를 위한 흡착제로 활용 시, 이차오염

우려는 없는 것으로 판단되었다.

제지슬러지와 중금속의 반응성을 평가하기 위하여 회분식 실험을

수행하였으며, 그 결과는 Langmuir 또는 Freundlich 모델식을

이용하여 분석하였다. 제지슬러지의 흡착 특성을 파악하기 위해,

양이온 및 음이온 중금속으로 각각 Cd과 As(Ⅴ)를 선정하였다. pH 4

조건에서의 제지슬러지의 카드뮴 최대흡착량은 112.52mg/g으로

중금속 흡착에 효과적으로 알려져 있는 제강슬래그의 카드뮴

최대흡착량 (29.2mg/g)보다 큼을 알 수 있었다.

또한 제지슬러지의 중금속 흡착능을 증가 시키기 위해,

화학적으로 개질하여, Cd과 As(Ⅴ)의 흡착능 증감을 평가하고자

하였다. 등온흡착 실험 결과, 제지슬러지에 수산화나트륨(NaOH)을

가하여 개질한 제지슬러지인 PMS-1의 경우 Cd에 대한 흡착능이

80%이상 증가하였다. 하지만 수산화나트륨(NaOH)과

타르타르산(C4H6O6)을 이용하여 개질한 PMS-2의 경우, 오히려

39

흡착능이 감소하였다. Cd과 달리 As(Ⅴ)의 흡착은 PMS-1과 PMS-2

모두 개질 전 제지슬러지에 비하여 흡착능이 감소하였다.

제지슬러지 개질 전-후의 Cd및 As(Ⅴ)의 흡착 메커니즘의 변화는

흡착제의 Zeta-potential 변위, FTIR, XRF 분석을 통해 설명하였다.

제지슬러지를 NaOH로 개질한 경우, Zeta-potential이 음(-)으로 대전

되었으며, 이로 인해 양이온성 중금속인 Cd 의 흡착능은 증가하나

음이온성 중금속인 As의 흡착능은 감소한 것으로 밝혀졌다. XRF

분석결과, PMS-1의 경우 개질 전 제지슬러지와 화학구성성분의

변화가 없는 반면, PMS-2의 경우 침전 기작을 통해 Cd 등 중금속을

제거할 수 있는 산화칼슘(CaO)과 chelating agent인 amine group이

감소하여, 중금속의 흡착능이 감소하였음을 알 수 있었다.

주요어 : 제지슬러지, 등온흡착실험, 제타포텐셜, 카드뮴, 비소,

화학적 개질

학 번 : 2012-23252