TREATMENT OF INDUSTRIAL WASTEWATERS BY … · ADSORBENTS AND INVESTIGATION OF ADSORBENTS CHARACTERISTICS by ... of particle size effect, ... A principal source of copper in industrial

TREATMENT OF INDUSTRIAL

WASTEWATERS BY USING SOME

ADSORBENTS AND INVESTIGATION OF

ADSORBENTS CHARACTERISTICS

by

Selin KUTLU

January, 2005

İZMİR

ABSTRACT

Industrial and municipal wastewaters frequently contain metal ions. These metal

ions, when present in sufficient quantity, can be harmful to aquatic life and human

health. Current methods for such wastewater treatment include precipitation,

coagulation/flotation, sedimentation, flotation, filtration, membrane process,

electrochemical techniques, ion exchange, biological process, and chemical reaction.

Each method has its merits and limitations in application. The adsorption process with

activated carbon is attracted by many scientists because of the effectiveness for the

removal of heavy metal ion at trace quantities.

Synthetic water containing zinc (Zn2+) and copper (Cu2+) metal ions was used as the

represent of industrial wastewater. The reason in choosing zinc and copper as metal

ions is that these metal ions are used in industry frequently and in large amounts. The

world’s zinc and copper production is still rising. This basically means that more and

more zinc ends up in the environment. In this study, two types of activated carbon

(produced from oak wood) and zeolite, modified with acid, were used in the study as

adsorbents. Due to the fact adsorption process has not been used extensively for its

high cost, the use of low cost materials as adsorbents for metal removal from

wastewater have been highlighted.

In thesis scope, while observing the removal efficiencies, adsorption characteristics

were investigated by means batch studies of particle size effect, pH effect, initial

concentration effect, contact time effect, and adsorbent dosage. Additional to these

parameters, the behavior of zinc and copper removal from single and

multi-component was also investigated.

ÖZET

Endüstriyel ve evsel nitelikteki atıksular sıklıkla metal iyonu içerirler. Bu metal

iyonları belirli miktarlarda bulundukları takdirde sucul yaşama ve insan sağlığına

zararları olabilir. Bu tür atıksuların arıtımı için mevcut yöntemler kimyasal çöktürme,

koagülasyon/flotasyon, çökeltim, flotasyon, filtrasyon, membran prosesleri,

elektrokimyasal teknikler, iyon değişimi, biyolojik prosesler ve kimyasal reaksiyon

gibi metotları kapsar. Her yöntemin belli bir değeri ve uygulamada kısıtları vardır.

Aktif karbonla adsorpsiyon prosesi, iz miktardaki ağır metal iyonlarının giderimindeki

veriminden dolayı birçok bilim adamı için çekim merkezi olmuştur.

Bu çalışmanın amacı, endüstriyel atıksuların, özellikle ağır metal içeren atıksuların

adsorpsiyon yöntemi ile potansiyel arıtımını, bazı adsorbanları ve adsorban

karakteristiklerini araştırmaktır. Bu çalışmada endüstriyel atıksuyu temsilen çinko

(Zn2+) ve bakır (Cu2+) metal iyonlarını içeren sentetik su kullanılmıştır. Metal iyonu

olarak çinko ve bakır metal iyonlarının seçilmesinin nedeni, bu metal iyonlarının

endüstride sıklıkla ve büyük miktarlarda kullanılmasıdır. Dünyanın çinko ve bakır

üretimi hala artmaktadır. Bu basit olarak, çinko ve bakır iyonlarının, her geçen gün

artan miktarlarda doğada son bulması anlamına gelir. Bu çalışmada adsorban olarak iki

tip aktif karbon (meşe odunundan üretilmiş) ve asit ile modifiye edilmiş zeolit

kullanılmıştır. Adsorpsiyon prosesinin yüksek maliyete sahip olmasından nedeniyle

yoğun olarak kullanılmamasından dolayı, düşük maliyete sahip adsorbanların metal

giderimi için kullanılması dikkati çekmiştir.

Tez kapsamında, giderim verimleri gözlenirken, adsorpsiyon karakteristikleri,

partikül boyutu etkisi, pH etkisi, başlangıç konsantrasyonu etkisi, temas süresi etkisi

ve adsorban dozu etkisi kesikli çalışmalar yardımıyla araştırılmıştır. Bu

parametrelere ek olarak, tekli ve çoklu bileşenli çözeltilerden çinko ve bakır giderim

davranışları ayrıca araştırılmıştır.

1. Introduction

Industrial wastewater is process and non-process wastewater generating from

manufacturing, commercial, mining, and silvicultural facilities or activities. This

includes the runoff and leachate from areas that receive pollutants associated with

industrial or commercial storage, handling or processing, and all other wastewater

not otherwise defined as domestic wastewater. In many countries, the wastes from

industrial processes are being produced in ever increasing amounts and may contain

toxic and poorly degradable compounds. They are often considerably stronger than

domestic sewage, which many treatment systems are only designed to handle.

Heavy metal pollution is of major concern to environmental scientists. Heavy

metals are present in nature and industrial wastewaters. Toxic pollution has received

a great deal of attention due to the increased industrialization, higher demand for

chemicals and higher contaminant production. With the development of

industrialization and human activities, the discharge of waste and wastewaters

containing heavy metals to the environment has increased.

The objective of the present study was to evaluate the treatment of industrial

wastewaters, particularly heavy metal bearing wastewaters by using some adsorbents

and to investigate the adsorption characteristics of adsorbents. Representing heavy

metal bearing wastewater, synthetic solution containing zinc and copper metal ions

separately and together; representing adsorbents, two types of activated carbon and

zeolite which modified with acid were used.

While investigating the adsorption characteristics of adsorbents, some effects and

how they’re affecting adsorption efficiencies were observed with some sets of

experiments. Experiments for characterizing adsorbent’s capacity were batch study

of particle size effect, pH effect, initial concentration effect, contact time effect,

adsorbent dose effect, and isotherm studies for Zn(II)(aq) and Cu(II)(aq).

2. Literature Survey

2.1. Industrial Wastewaters

Industrial wastewater is process and non-process wastewater generating from

manufacturing, commercial, mining, and silvicultural facilities or activities. This

includes the runoff and leachate from areas that receive pollutants associated with

industrial or commercial storage, handling or processing, and all other wastewater

not otherwise defined as domestic wastewater. In many countries, the wastes from

industrial processes are being produced in ever increasing amounts and may contain

toxic and poorly degradable compounds. They are often considerably stronger than

domestic sewage, which many treatment systems are only designed to handle.

Waterborne wastes present a potential hazard to natural water systems. These

wastes can contain either organic matter, which causes deoxygenation by promoting

microbial activity or material that is directly toxic to the various life forms in the

systems. Treatment of these wastes is therefore of paramount importance. Inorganic

and organic pollutants can be dangerous to environment in many ways. Each of these

pollutants can affect living’s life in a different way, directly, or indirectly.

2.2. Heavy Metals in Wastewaters

Various types of heavy metals are widely used in industry, almost every type of

industry has certain metals in their wastewaters. Heavy metals are natural

components of the Earth’s crust. They cannot be degraded or destroyed. Heavy

metals are dangerous because they tend to bioaccumulate. Heavy metals can enter a

water supply by industrial and consumer waste, or even from acidic rain breaking

down soils and releasing heavy metals into streams, lakes, rivers, and groundwater.

There are some heavy metals which are widely used among the other heavy

metals. The two of these heavy metals are zinc and copper. These pollutants are in

large amounts in wastewaters when used in a various industrial processes.

2.3. Sources and Treatment Methods of Zinc and Copper Bearing Wastewaters

There are so many industries discharging waste streams which contain significant

zinc levels. These industries include steel works with galvanizing lines, zinc and

brass metal works, zinc and brass plating, viscose rayon yarn and fiber production,

groundwood pulp production, newsprint paper production. Zinc salts used in the

inorganic pigments industry (e.g., zinc chromate). High zinc levels may be observed

in acid mine drainage water. Zinc compounds have many uses, from smoke bombs

through batteries and wood preservatives to food supplements and drugs. The

primary source of zinc in wastewaters from plating and metal-processing industries is

the dragout solution adhering to the metal product after removal from pickling or

plating baths. The metal is rinsed free of this solution and the contaminants are thus

transferred to the rinsewater. Plating solutions typically contain 5000-34000 mg/l

zinc.

Many industries discharging waste streams which contain significant copper

levels include metal-cleaning and metal-plating baths and rinses, copper plating for

silver and other precious metals in jewelry, manufacture of printed circuit boards,

copper-bearing mining and acid mine drainage, pulp, paper and paper board mills,

chlorosilane (silicone) synthesis, wood preserving, fertilizer manufacturing,

petroleum refining, paint and pigment manufacturing, basic steel works and

foundries, nonferrous metal works and foundries, motor vehicle and aircraft plating

and finishing. A principal source of copper in industrial waste streams is metal-

cleaning and metal-plating baths and rinses. Brass and copper metal working requires

periodic oxide removal by immersing the metals in strong acid baths. Solution

adhering to the cleaned metal surface, referred to as dragout, is rinsed from the metal

and contaminates the waste rinsewater. Copper concentration in the plating bath

depends upon the bath type, and may range from 3000 to 50000 mg/l.

Although some preventive actions have been adopted by several methods to

remove heavy metals from their effluent, in particular, chemical precipitation is the

most prevalent. Treatment processes employed for zinc removal from wastewater

may involve either chemical precipitation, with disposal of the resultant sludge, or

recovery. Recovery may be applied by ion exchange, evaporative recovery, and other

processes including precipitation, where relatively pure zinc sludge is reclaimed.

Recovery of plating wastes may prove to be more economical on an overall basis

than is conventional precipitation and sludge disposal.

In the treatment of copper bearing wastewaters, precipitation with lime is

predominantly used treatment method. Process modification and waste stream

segregation provide means of enhanced treatment of copper-bearing wastes.

Cementation is another process with significant potential application for both

concentrated and dilute copper wastewaters. Electrodialysis has been cited as

economically feasible for treatment of process solutions and rinsewaters from plating

and metal-finishing operations. Granular activated carbon and reverse osmosis

treatments are alternative methods for copper removal..

2.4. Adsorption

Adsorption is a process by which material accumulates at the interface between

two phases as liquid-liquid, gas-liquid, or liquid-solid. The adsorbing phase is called

the adsorbent, and any substance being adsorbed is termed as an adsorbate.

Adsorption onto solid adsorbents has great environmental significance, since it can

effectively remove pollutants from both aqueous and gaseous streams. Due to the

high degree of purification that can be achieved, this process is often used at the end

of a treatment sequence.

While evaluating the adsorption systems, isotherms are used. Freundlich and

Langmuir isotherms were used in this study. The linearized form of the Freundlich

and Langmuir isotherms can be written as;

log qe = log KF + 1/n log C (Freundlich Isotherm)

C/qe = 1/(bQ0) + C/Q0 (Langmuir Isotherm)

where C (mg/l) is the equilibrium concentration, qe (mg/g) is the amount adsorbed at

equilibrium, and KF and n are the constants that can be related to the adsorption

capacity and the adsorption intensity, respectively, and b (l/mg) is the “affinity”

parameter or the Langmuir constant, and Q0 (mg/g) is the “capacity” parameter.

In the application of adsorption for purification of wastewaters, the material to be

adsorbed commonly will be a mixture of many compounds rather than a single one.

The compounds may mutually enhance adsorption, may act relatively independent,

or may interfere with one other.

Since its first introduction for heavy metal removal, activated carbon has

undoubtedly been the most popular and widely used adsorbent in wastewater

treatment applications throughout the world. In spite of its prolific use, activated

carbon remains an expensive material since the higher the quality of activated

carbon, the greater its cost. Due to the problems mentioned previously, research

interest into the production of alternative adsorbents to replace the costly activated

carbon has intensified in recent years. Because of their low cost and local

availability, natural materials such as chitosan, zeolites, clay, or certain waste

products from industrial operations such as fly ash, coal, and oxides are classified as

low-cost adsorbents.

3. Experimental

3.1. Preparation of Adsorbents Used

Batch removal of Zn(II)(aq) and Cu(II)(aq) ions from aqueous solutions with two

types of activated carbons (Type1 AC, Type2 AC) and one type of zeolite which was

modified with acid was studied. Natural zeolite, as clinoptilolite

(Na6[Al6Si3O72].24H2O), from Bigadiç region, used in this study, was supplied by

Department of Mining Engineering, Dokuz Eylül University. Two types of activated

carbon, used in the experiments, were supplied by TEKNOPARK Aktif Karbon

Teknoloji Sitesi San. ve Tic. A. Ş. Activated carbon and zeolite samples were

screened through Retsch Test Sieve ASTM 5, 10, 18, 35, and 60 mesh sieves prior to

use in the experiments. Then screened zeolite was modified with applying 30%

sulfuric acid solution in a sealed 300 ml Erlenmeyer conical flask placing on an

orbital shaker and shaking at 250 rpm for 0.5 h at room temperature. After shaking,

all screened zeolite were washed with distilled water and then oven dried at 103°C

for 1 h. After screening, activated carbon samples were not applied any treatment,

only washed with distilled water and then were oven dried at 103°C for 1 h. The

dried adsorbent samples were kept in closed jars.

Table 1. Chemical structure of zeolite which is used in the experiments (%).

SiO2 Al2O3 Fe2O3 MgO CaO Na2O K2O MnO 69.44 12.25 0.88 1.20 2.21 - 3.52 0.001

3.2. Stock and Reference Solutions

2.084 g of ZnCl2 (solid) and 2.682 g of CuCl2.2H2O (solid) were dissolved in

1000 ml of distilled water to obtain a 1000 ppm stock solution of Zn(II)(aq) and

Cu(II)(aq). These stock solutions were appropriately diluted to obtain the

concentrations used in the experiments.

3.3. Analysis of Solution Sample

The concentration of Cu, Zn in the solutions was determined by atomic absorption

spectrophotometry using direct aspiration technique (EPA, 1986). Zinc was analyzed

by flame atomic absorption spectrometry using ATI Unicom 929 Atomic Absorption

Spectrometer with the wavelength of 213.9 nm. Copper was analyzed by flame

atomic absorption spectrometry using ATI Unicom 929 Atomic Absorption

Spectrometer with the wavelength of 324.7 nm.

3.4. Batch Adsorption Studies

In all batch adsorption studies, 250 ml Erlenmeyer flask containing 100 ml of

metal solution were used. Mixtures were shaken with IKA Labortechnik TS 501

Digital shaker at 210 rpm. The pH of the metal solutions and adsorbent-solution

mixtures was measured by using Lutron PH206 instrument with temperature

compensation ability. After shaken for a defined equilibrium time, the samples were

filtered and filtrate was acidified with HNO3 before measuring the equilibrium

concentration of metal in the filtrate.

In order to investigate the effect of particle size on adsorption, adsorbents were

separated into four particle size. Particle sizes used in this experiment were

0.25-0.50 mm, 0.50-1.00 mm, 1.00-2.00 mm, and 2.00-4.00 mm. Batch studies were

conducted by contacting 0.5 g of adsorbents in four particle size separately with

approximately 10 mg/l Zn(II)(aq) and 25 mg/l Cu(II)(aq) solution. Adsorbents and

metal salt solutions were shaken for 1 h. Initial pH values were varying in the range

of 4.50-5.70 for Zn(II)(aq) solution, while of 5.65-5.80 for Cu(II)(aq).

In order to investigate the effect of pH on adsorption, approximately 10 mg/l

Zn(II)(aq) solution with initial pH values varying 2 to 7 and 25 mg/l Cu(II)(aq) solution

with initial pH values varying 2.5 to 5. These pH values were chosen from the pH

range that there would be no precipitation of zinc and copper. The pH values of the

solution sample were adjusted using 0.1 M H2SO4, or NaOH. 0.25 g of adsorbents in

the particle size range of 0.25-0.50 mm was shaken for 1 h.

In order to investigate the effect of initial concentration on adsorption, solutions

with initial concentrations varying 7 to 1400 mg/l Zn(II)(aq) and 26 to 1080 mg/l

Cu(II)(aq). Initial pH values were varied in the range of 5-6.5 for zinc adsorption, and

4.90-5.85 for copper adsorption. The mixture containing 0.25 g adsorbents in the

particle size range of 0.25 mm-0.50 mm and metal solution was shaken for 1 h.

In order to investigate the effect of contact time on adsorption, 0.25 g of

adsorbents in the particle size of 0.50-1.00 mm range and 25.525 mg/l of Zn(II)(aq)

and 22.04 mg/l of Cu(II)(aq) solution were shaken for time intervals varying 5 to 540

min. The aim of choosing and using these time intervals is to allow the adsorption to

reach equilibrium and define the equilibrium time for adsorbents in adsorption of

both two ions from the single solutions. Initial pH value was 6.15 for zinc and 5.65

for copper adsorption.

In order to investigate the effect of adsorbent dose on adsorption, adsorbent doses

were selected varying 1.5 to 6.5 g/l. Adsorbents in 0.50-1.00 mm particle size and the

initial concentrations of 21.40 mg/l Zn(II)(aq) at pH 6.03, and 17.16 mg/l Cu(II)(aq) at

pH 5.35 were used. The contact time which was used for the adsorbents were the

equilibrium times which were taken from the results of contact time effect.

Batch isotherm studies were conducted by contacting adsorbents in the particle

size range of 0.50-1.00 mm, with 21.40 mg/l of Zn(II)(aq) and 17.16 mg/l of Cu(II)(aq)

solution. Adsorbent’s amount varied in the range of 0.00-0.65 g. The mixture was

shaken at the time interval determined in the contact time effect study above.

In the batch multi-component adsorption study, competitive adsorption of

Zn(II)(aq) and Cu(II)(aq) ions from their binary solutions was investigated. The initial

metal ion concentrations were chosen as 12.45 mg/l for Zn(II)(aq) and 10.49 mg/l for

Cu(II)(aq) metal ion. These metal solutions were mixed in the ratio of 1:1, and 0.25 g

(0.50-1.00 mm) Type1 AC adsorbent was added to the metal mixture solution at pH

5.06. The mixture was shaken for the time interval varying 5 to 540 min.

4. Results and Discussion

The amount of the metal ion adsorbed (removed from solution) per unit mass of

adsorbents (Type1 AC, Type2 AC, and modified zeolite) was evaluated by the

following expression:

Metal ion adsorbed (removed from solution) = (C0 – C) .V/m

Here, C0 and C are the concentrations of metal in aqueous phase before and after

equilibrium in mg/l, respectively, and m is the amount of the adsorbent used in g, and

V is the volume of solution in l.

Adsorption isotherms have been analyzed in terms of the Langmuir equation due

to adsorbents best fitted to Langmuir isotherm. Langmuir equation is as following:

C/qe = 1/(bQ0) + C/Q0

C (mg/l) is the equilibrium concentration, qe (mg/g) is the amount adsorbed at

equilibrium, and b (l/mg) the “affinity” parameter or the Langmuir constant, and Q0

(mg/g) is the “capacity” parameter. When C/qe is plotted versus C, the slope is equal

to 1/Q0 and the intercept is equal to 1/Q0b.

The essential characteristics of a Langmuir isotherm can be expressed in terms of

a dimensionless constant separation factor or equilibrium parameter, RL, which

describes the type of isotherm and is defined by,

RL = 1

1 + bC0

where, b (l/mg) is the Langmuir constant and C0 (mg/l) the initial concentration of

solute. RL indicates the type of isotherm as follows:

Table 2. Equilibrium parameter, RL.

Value Type of isotherm RL > 1 Unfavorable RL = 1 Linear 0 < RL < 1 Favorable RL = 0 Irreversible

4.1. Effect of Particle Size

It’s been pointed by Ricordel et al. (2001) that particle size is an important factor

in adsorption kinetics because it determines the time required for transport within the

pore to adsorption sites. When the same carbon dosage was used, the equilibrium

time is less for smaller size, which can reduce significantly the carbon usage rate.

The effect of particle size to the adsorption of Zn(II)(aq) and Cu(II)(aq) is shown in

Figures 1-4. As it’s seen from the figures, adsorption efficiency has the best value at

finest particle size as 0.25-0.50 mm range for both metal ions and the best adsorption

efficiencies were found to be 96.50% and 85.6% for zinc and copper, respectively. A

decrease in the particle size resulted in an increase in adsorption efficiency.

0102030405060708090

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0.25 - 0.50mm

0.50 - 1.00mm

1.00 - 2.00mm

2.00 - 4.00mm

Particle Size

Ads

orpt

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Effi

cien

cy, %

Type1 ACType2 ACZeolite

0

1

2

3

0.25 - 0.50mm

0.50 - 1.00mm

1.00 - 2.00mm

2.00 - 4.00mm

Particle Size

Rem

oved

Zn(

II) (a

q), m

g/g


Figure 1. Effect of particle size to the

adsorption efficiency of Zn(II)(aq).

Figure 2. Effect of particle size to the adsorbed Zn(II)(aq) amount.

0102030405060708090

100

0.25 - 0.50mm

0.50 - 1.00mm

1.00 - 2.00mm

2.00 - 4.00mm

Particle Size

Ads

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Effi

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cy, %


0

1

2

3

4

5

0.25 - 0.50mm

0.50 - 1.00mm

1.00 - 2.00mm

2.00 - 4.00mm

Particle Size

Rem

oved

Cu(

II) (a

q), m

g/g


Figure 3. Effect of particle size to the

adsorption efficiency of Cu(II)(aq). Figure 4. Effect of particle size to the adsorbed Cu(II)(aq) amount.

As it can be seen from the Figures 1-4, decreasing particle size resulted in an

increase in adsorption capacity (mg/g) which resulted in an increase in adsorption

efficiency for all adsorbents. This situation is probably because of the larger surface

area available. Banat et al. (2000) pointed that the increase in the sorption capacity is

attributed to the increase in the external surface area of the sorbent available for

adsorption. Many researchers (Al-Asheh, & Duvnjak, 1997; Mellah, & Chegrouche,

1997; Ajmal et al., 1998; Banat, et al, 2000; Ajmal, Rao R. A. K, Ahmad,R., Ahmad

J., & Rao L. A. K., 2001; Kandah, 2001; Ricordel, et al, 2001; Ho et al., 2002;

Boonamnuayvitaya et al., 2004) reported the result from their studies, while studying

on the removal of zinc and/or copper, about particle size effect for the adsorbents of

pine bark, natural bentonite, sawdust, dried animal bones, kyanite, sheep manure

waste, peanut husks carbon, tree fern, and pyrolyzed coffee residues+clay,

respectively, that the decrease in the particle sizes led in an increase in the metal

uptake per unit weight of the sorbent.

According to these summarized results, adsorbent with the particle size of

0.25-0.50 mm was selected for the other adsorption studies (pH effect, initial

concentration effect) due to the sufficient adsorption capacity comparing the other

particle size ranges tried.

4.2. Effect of pH

The pH of the aqueous solution is an important controlling parameter in the

adsorption process and the removal of pollutants from wastewaters by adsorption

is highly dependent on pH of the solution which affects the surface charge of the

adsorbent, and the degree of ionization and speciation of adsorbate as suggested

by Elliott and Huang (1981).

The effect of initial solution pH to the sorption of metals on Type1 and Type2

AC, and acid modified zeolite is shown in Figures 5-8. Generally the sorption

quantity of all metals increases with the increasing pH values. Kandah (2004)

reported that the reason of the low adsorption of metals at lower pH values might be

due to that a higher concentration of H+ in the solution competes with metal ions for

adsorption sites, resulting in the reduced uptake of metal ion. As pH increases, the

concentration of H+ decreases and the concentrations of metal ions remain constant.

Therefore, a competition in the adsorption process between H+ and metal ions

becomes more evident for low pH values.

-20

0

20

40

60

80

100

1 2 3 4 5 6 7 8pH

Ads

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ion

Effi

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cy, %


-1

0

1

2

3

4

5

6

1 2 3 4 5 6 7 8pH

Rem

oved

Zn(

II) (a

q), m

g/g Type1 AC

Type2 ACZeolite

Figure 5. Effect of solution pH to the

adsorption efficiency of Zn(II)(aq). Figure 6. Effect of solution pH to the adsorbed Zn(II)(aq) amount.

0

10

20

30

40

50

60

2 3 4 5 6pH

Ads

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Effi

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Type2 ACZeolite

0

1

2

3

4

5

6

2 3 4 5 6

pH

Rem

oved

Cu(

II) (a

q), m

g/g Type1 AC

Type2 ACZeolite

Figure 7. Effect of solution pH to

the adsorption efficiency of Cu(II)(aq).

Figure 8. Effect of solution pH to the adsorbed Cu(II)(aq) amount.

Figures 5-6 revel that the maximum uptake of zinc and the maximum adsorption

efficiency took place at pH 7.03 for Type1 and Type2 AC. The adsorption

efficiencies were 85.9% and 56.9%, respectively. Acid modified zeolite showed

removal efficiency of 4.8% only at pH 3.5. At the other pH values, there can be seen

desorption with the pH values of 2.03, 5.01, and 7.03. This situation may be

attributed to that zeolite showed more attraction to the water molecules than Zn(II)(aq)

at these pHs, so the concentration of zinc per the volume of solution increased, and

this situation lead to that there was a desorption. As a result, it can be said for the

adsorption of zinc on Type1 and Type2 AC that the percent adsorption efficiency and

removed Zn(II)(aq) increases with increasing pH.

It can be seen from Figures 7-8 that the maximum adsorption efficiency showed

peak value at pH 4.50 for all type of adsorbents for the removal of Cu(II)(aq). The

adsorption efficiencies were 51.7%, 45.7%, and 23.4% for Type1 AC, Type2 AC,

and acid modified zeolite, respectively. As a result, it can be said for the adsorption

of copper on the adsorbents in this study that the percent adsorption efficiency

increases until to reach the peak value (pH 4.5) and then decrease; and the removed

Cu(II)(aq) increases with increasing pH for all adsorbents.

4.3. Effect of Initial Concentration

Adsorption process is not efficient when high concentration of contaminants is

under consideration. It can be seen from Figures 9-12. After passing some certain

levels of initial concentration, the adsorption efficiency decreased sharply. Generally,

the plotted data indicated that the raising concentration values decreased adsorption

efficiencies and increased the metal uptake of both metals.

Data plotted in the Figures 9-12, the removal efficiencies by Type1 AC were

98.1% for 7.227 mg/l, and 96.5% for 11.235 mg/l Zn(II)(aq), and 54.9% for

26.09 mg/l Cu(II)(aq); by Type2 AC were 81.4% for 7.227 mg/l, and 96.5% for

11.235 mg/l Zn(II)(aq), and 49.9% for 26.09 mg/l Cu(II)(aq); by zeolite were 13.6% for

7.227 mg/l, and 25.9% for 11.235 mg/l Zn(II)(aq), and 26.2% for 26.09 mg/l Cu(II)(aq).

There is a general opinion that the percentage adsorption for metal ions decreases

with increasing metal concentration in aqueous solutions. It was pointed that this

result indicates that energetically less favorable sites become involved with

increasing metal concentrations in the aqueous solution (Erdem et al., 2004).

0102030405060708090

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0 500 1000 1500C0, mg/l Zn(II)(aq)

Ads

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Effi

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0102030405060708090

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0 500 1000 1500C0, mg/l Zn(II)(aq)

Rem

oved

Zn(

II) (a

q), m

g/g


Figure 9. Effect of C0 to the

adsorption efficiency of Zn(II)(aq). Figure 10. Effect of C0 to the adsorbed Zn(II)(aq) amount.

0

10

20

30

40

50

60

0 400 800 1200C0, mg/l Cu(II)(aq)

Ads

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Effi

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0

10

20

30

40

50

60

0 400 800 1200C0, mg/l Cu(II)(aq)

Rem

oved

Cu(

II) (a

q), m

g/g


Figure 11. Effect of C0 to the

adsorption efficiency of Cu(II)(aq). Figure 12. Effect of C0 to the adsorbed Cu(II)(aq) amount.

4.4. Effect of Contact Time

The contact time is an important parameter in adsorption. Generally, increasing

contact time results in an increase in adsorption efficiency until the point at that there

is no significant change in the removal reached. This point is called equilibrium time.

As it’s seen from the Figures 13-16, the adsorption efficiency and the absolute

amount of metal ion adsorbed per unit of adsorbent increases with the increase in

time for both metal ion. The equilibrium times on which decided were 390, 300, and

300 min for the removal of Zn(II)(aq) for Type1 AC, Type2 AC, and modified zeolite,

respectively; and were 180, 240, and 30 min for the removal of Cu(II)(aq) for Type1

AC, Type2 AC, and modified zeolite, respectively. As it’s seen from these values,

Type1 AC, Type2 AC, and modified zeolite reaches equilibrium earlier in the

removal of copper than the removal of zinc. The isotherm studies were conducted

using these values.

The plotted figures showed the rate of percent removal is higher at the beginning

and it can be attributed to the larger surface area of the adsorbent being available at

beginning for the adsorption of metals. As the surface adsorption sites become

exhausted, the uptake rate is controlled by the rate at which the adsorbate is

transported from the exterior to the interior sites of the adsorbent particles (Yu et al.,

2000).

0102030405060708090

0 200 400 600

Time (min)

Ads

orpt

ion

Effi

cien

cy, %

Type1 AC

Type2 AC

Zeolite

0123456789

0 200 400 600

Time (min)

Rem

oved

Zn(

II) (a

q), m

g/g

Type1 AC

Type2 AC

Zeolite

Figure 14. Effect of contact time

to the adsorbed Zn(II)(aq) amount.

Figure 13. Effect of contact time to the adsorption efficiency of

Zn(II)(aq).

0102030405060708090

100

0 200 400 600

Time (min)

Ads

orpt

ion

Effi

cien

cy, %


0123456789

0 200 400 600

Time (min)

Rem

oved

Cu(

II) (a

q), m

g/g


Figure 15. Effect of contact time

to the adsorption efficiency of Cu(II)(aq).

Figure 16. Effect of contact time to the adsorbed Cu(II)(aq) amount.

4.5. Effect of Adsorbent Dose

Another important factor that should be considered in adsorption process is the

adsorbent dose. Due to the fact that the efficient use of adsorbent is only possible by

studying on the parameters mentioned before with the optimum adsorbent dose to get

maximum efficiency. It was reported that an increase in the adsorbent dosage

resulted in a decrease in the contact time required to reach apparent equilibrium

(Chu, & Hashim, 2002). For a fixed initial solute concentration, increasing total

sorbent doses provides a greater surface area (or sorption sites), so the removal of

metal by adsorption is increased (Ho, & McKay, 2004).

The contact times used for the adsorbents were not the same due to the fact that

the equilibrium times taken from the results of contact time effect for efficient use

were used separately for Zn(II)(aq) and Cu(II)(aq) metal ions. So this fact must be

considered while comparing the results of removal efficiencies of the adsorbents, this

comparison are not as a function of same time interval. The conducted contact times

were 390, 300, 300 min for the removal of Zn(II)(aq), and 180, 240, 30 min for the

removal of Cu(II)(aq) by Type1 AC, Type2 AC, and modified zeolite, respectively.

Increase in Type1 AC and Type2 AC doses resulted in an increase in the removal

efficiency, while adsorption capacity decreased with increase in adsorbent dose. The

decrease in adsorption capacity may be due to the fact that some adsorption sites may

remain unsaturated during the adsorption process whereas the number of sites

available for adsorption site increases by increasing the adsorbent doses and that

results in the increase of removal efficiency (Sharma, & Forster, 1993). Increasing

zeolite dose results in a decrease in adsorption efficiency (%), and a decrease in

adsorbent capacity (mg/g). This indicates that there is no adsorption, but desorption

in every dose applied for contact time of 300 min and at pH 6.03. This situation may

be attributed to that while increasing zeolite dose, available surface area for

adsorption would also increase. If these areas shows more affinity to water than to

Zn(II)(aq), and so selects water, zinc concentration in solution would increase per unit

volume of solution. Due to the fact that it would seem there is desorption, because

zinc concentration in solution increases per unit volume of solution.

0102030405060708090

100

1 3 5 7Adsorbent Dose, g/l

Ads

orpt

ion

Effi

cien

cy, %


0

1

2

3

4

5

6

7

1 3 5 7Adsorbent Dose, g/l

Rem

oved

Zn(

II) (a

q), m

g/g


Figure 18. Effect of adsorbent dose to the adsorbed Zn(II)(aq)

amount.

Figure 17. Effect of adsorbent dose to the adsorption efficiency

of Zn(II)(aq).

-80

-60-40

-200

2040

6080

100

1 3 5 7

Adsorbent Dose, g/l

Ads

orpt

ion

Effi

cien

cy, %


-8

-6

-4

-2

0

2

4

6

8

1 3 5 7

Adsorbent Dose, g/l

Rem

oved

Cu(

II) (a

q), m

g/g

Type1 AC

Type2 AC

Zeolite

Figure 19. Effect of adsorbent

dose to the adsorption efficiency of Cu(II)(aq).

Figure 20. Effect of adsorbent dose to the adsorbed Cu(II)(aq)

amount.

Increase in Type1 AC dose made an increase in adsorption efficiency, and a

decrease in absorbed Cu(II)(aq) amount on adsorbent. As to the Type2 AC, increasing

dose did not make significant difference in adsorption efficiency; there was a

decrease in absorbed Cu(II)(aq) amount on adsorbent, but no significant increase of

adsorption removal. It can be said that increase in Type2 AC dose does not make

difference in removal efficiency. As it’s seen from the Figures 19-20, for the

modified zeolite doses of 1.5 and 2.5 g/l, there was no adsorption, but desorption.

Increasing zeolite dose resulted in an increase in adsorption efficiency (%), and

increase in adsorbent capacity (mg/g). This result is similar to the study by Gupta, &

Ali (2000).

4.6. Batch Isotherm Studies

The adsorption data of Type1 AC, Type2 AC, and modified zeolite as a function

of adsorbent dose correlates well with the Langmuir isotherm. The linearized form of

the Langmuir isotherm can be written as:

C/qe = 1/ (bQ0) + C/Q0

C (mg/l) is the equilibrium concentration, qe (mg/g) is the amount adsorbed at

equilibrium, and b (l/mg) the “affinity” parameter or the Langmuir constant, and Q0

(mg/g) is the “capacity” parameter. When C/qe is plotted versus C, the slope is equal

to 1/Q0 and the intercept is equal to 1/Q0b.

Table 3. Langmuir constants (Q0 and b) and equilibrium parameter, RL for

Zn(II)(aq) and Cu(II)(aq).

Metal Ion

Adsorbent Type Q0, (mg/g) b, (l/mg) r2 RL Type of

Isotherm Type1AC 6,035 5,487 0,9987 0,008 favorable Type2 AC 3,821 0,652 0,999 0,067 favorable Zn(II)(aq) Zeolite 0,019 -0,055 0,9992 -5,594 Type1AC 6,930 1,152 0,9904 0,048 favorable Type2 AC 0,267 -0,172 0,9983 -0,512 Cu(II)(aq) Zeolite 1,910 -2,055 0,9815 -0,029

In the Table 3, Langmuir constants and equilibrium parameters belonging to

Type1 AC, Type2 AC, and modified zeolite adsorbents for the removal of Zn(II)(aq)

and Cu(II)(aq). If the adsorption capacities for Zn(II)(aq) removal of the adsorbents are

to be compared there is the order of: Type1 AC > Type2 AC > Zeolite; for Cu(II)(aq)

removal, there is the order of: Type1 AC > Zeolite > Type2 AC.

4.7. Batch Multi-component Adsorption Study

Mohan, & Singh (2002) reported that adsorption in multi-component systems are

complicated because of the fact that solute–surface interactions are involved.

McKay, & Porter (1997) describes multi-component systems as “the systems which

are characterized by additional features from those of single components” and

mention about some interaction effects “between different species in solution and

potential interactions on the surface in particular depending on the sorption

mechanism and reversibility versus irreversibility”. In multi-component systems

there is a competition between the different metal ion species for the surface sites.

In this experiment, competitive adsorption of Zn(II)(aq) and Cu(II)(aq) ions from

their binary solutions was investigated. The initial metal ion concentrations were

12,45 mg/l for Zn(II)(aq) and 10,49 mg/l for Cu(II)(aq) metal ion. These metal

solutions were mixed in the ratio of 1:1, and 0.25 g (0.50-1.00 mm Type1 AC). The

contact time was 540 min.

0102030405060708090

100

0 200 400 600Time (min)

Ads

orpt

ion

Eff

icie

ncy,

%

of Zn(II) from multi-component solution

of Cu(II) from multi-component solution 0

1

2

3

4

5

0 200 400 600Time (min)

Rem

oved

met

al io

n, m

g/g

Zn(II) adsorption frommulti-component solutionCu(II) adsorption frommulti-component solution

Figure 22. Adsorbed Zn(II)(aq)

and Cu(II)(aq) amount from multi-component solution.

Figure 21. Adsorption efficiency of Zn(II)(aq) and Cu(II)(aq) from

multi-component solution.

As it’s seen from the Figures 21-22, Cu(II)(aq) was better adsorbed than Zn(II)(aq)

by Type1 AC from binary component solution. In Figure 23, it can be seen the

comparison of Zn(II)(aq) and Cu(II)(aq) metal ion adsorption from single and multi-

component solution as a function of time.

As it’s seen from Figure 23, the concentration of Zn(II)(aq) in binary component

solution is only half of the concentration in single-component solution. Even in this

situation, Zn(II)(aq) is better adsorbed from single-component solution. Because in

multi-component solution, there is another metal ion which competing with Zn(II)(aq)

to take the available surface area for adsorption.

Zn(II)(aq) and Cu(II)(aq) uptake from single component solution is much more than

binary component solution. Cu(II)(aq) is better adsorbed even in multi-component

solution as in single component solution.

0123456789

0 200 400 600Time, min

Rem

oved

Met

al Io

n, m

g/g

Cu(II) adsorption from 22,040 mg/l Cu(aq) single-component solution Zn(II) adsorption from 25,525 mg/l Zn(aq) single-component solution Cu(II) adsorption from 12,45 mg/l Zn(aq) + 10,49 mg/l Cu(aq) multi-component solution Zn(II) adsorption from 12,45 mg/l Zn(aq) + 10,49 mg/l Cu(aq) multi-component solution

Figure 23. Adsorbed Zn(II)(aq) and Cu(II)(aq) amount from single and multi-

component solution.

5. Conclusion

The following conclusions can be drawn from the study:

• The adsorption in these systems is highly dependent on particle size, pH, initial

metal concentration, contact time, and adsorbent dosage.

• If there would be any comparison for the effectiveness of the adsorbents in this

study, Type1 and Type2 activated carbons showed to be more effective for

Zn(II)(aq); and Type1 AC and modified zeolite showed to be more effective for

Cu(II)(aq) removal from aqueous solutions.

• The finest particle size (0.25-0.50 mm) showed the best removal efficiency for all

adsorbents, which is probably because of the larger surface area available, and

the increase in the external surface area of the sorbent available for adsorption.

• While Type1 AC, and Type2 AC showed best efficiency at pH 7.03; modified

zeolite at pH 3.50 for Zn(II)(aq) removal; all the adsorbents showed the best

efficiency at pH 4,49 for Cu(II)(aq) removal.

• An increase in the Zn(II)(aq) and Cu(II)(aq) concentration of the metal solution

resulted in an increase in the metal uptake per unit weight of the sorbent, but

decrease in the removal efficiency for Type1 AC, Type2 AC, and modified

zeolite. The best adsorption performances were obtained in low concentrations.

• The percentage of Zn(II)(aq) and Cu(II)(aq) removal is increasing with increase in

time until equilibrium was reached with all adsorbents used in this study.

• The equilibrium times for the removal of Zn(II)(aq) from solution were observed

for Type1 AC, Type2 AC, and zeolite as 390 min, 300 min, and 300 min,

respectively. For the removal of Cu(II)(aq) from solution, the equilibrium times

were observed for Type1 AC, Type2 AC, and zeolite as 180 min, 240 min, and

30 min, respectively. The adsorbents reached equilibrium for Cu(II)(aq) earlier

than Zn(II)(aq).

• Increase in adsorbent dose made an increase in adsorption efficiency, and a

decrease in absorbed amount on adsorbent for Type1 and Type2 activated

carbons, made a decrease in the adsorption efficiency, and a decrease in adsorbed

amount on modified zeolite for the removal of Zn(II)(aq).

• Increase in adsorbent dose made an increase in adsorption efficiency, and a

decrease in absorbed amount on adsorbent for Type1 AC for the removal of

Cu(II)(aq). As to the Type2 AC, increase in the dose did not make significant

difference in adsorption efficiency, and make a decrease in absorbed amount on

adsorbent, but there is no significant increase of adsorption removal. Increasing

zeolite dose caused an increase in the adsorption efficiency (%), and adsorbent

capacity (mg/g).

• The Langmuir isotherm successfully represented the adsorption phenomenon at a

specific pH value. Hence, the Langmuir equation can be used to determine the

amount of adsorbent required for the removal of Zn(II)(aq), and Cu(II)(aq) from the

wastewater.

• Langmuir constant, Q0 (mg/g) for Type1 AC, Type2 AC, and modified zeolite for

the removal of Zn(II)(aq), indicating adsorption capacities are 6,035 mg/g, 3,821

mg/g, and 0,019 mg/g, respectively. RL values which indicates the type of

Langmuir isotherm, as unfavorable, linear, favorable, and irreversible, is

favorable for Type1 AC, and Type2 AC.

• For the removal of Cu(II)(aq), Langmuir constants, Q0 (mg/g) of Type1 AC,

Type2 AC, and modified zeolite, are 6,930 mg/g, 0,267 mg/g, 1,910 mg/g. Only

the RL value of Type1 AC is favorable.

• Zn(II)(aq) and Cu(II)(aq) uptake from single component solution is much more than

binary component solution.

• Cu(II)(aq) is better adsorbed by Type1 AC than Zn(II)(aq). Considering uptakes of

Zn(II)(aq) and Cu(II)(aq) by Type1 AC, the order of Cu(II)(aq) > Zn(II)(aq) is true for

both from single component solution and binary component solution.

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