CHAPTER 1 INTRODUCTION - Shodhgangashodhganga.inflibnet.ac.in/bitstream/10603/9979/6/06_chapter 1.pdf · choosing adsorbents under optimum operating conditions. Therefore, the adsorption

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CHAPTER 1

INTRODUCTION

1.1 INTRODUCTION TO HEAVY METALS

Cities and metropolis with uncontrolled growth of population

produce large quantities of waste water containing toxic compounds in

relatively small and confined areas either during the production, storage,

transport, use or disposal of industrial products, thus interfering with the eco

system. Among these compounds, heavy metals are considered as hazardous

pollutants due to their toxicity even at low concentration and their

nonbiodegradability. Increased industrialization and discharge of wastes has

resulted in an unprecedented increase in heavy metal influx into natural water

bodies. The alarmingly high levels of heavy metals in natural water bodies

pose a serious threat to human health, living resources and ecological

systems. The removal of toxic metal ions from waste water is an important

and widely studied research area in water treatment. It is, therefore, essential

to reduce the heavy metal concentration in effluents before they are

discharged into the water bodies. Therefore, in research priority is given to

regulating these pollutants at the discharge level. In recent years, the issues

regarding disposal and treatment of effluent containing heavy metal pollutants

has become a rising concern to the public. Several attempts have been made

for their elimination, the objective being to design an effective and economic

process.

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Heavy metals include all metals with an atomic weight greater than

23 and a specific gravity of more than 5. The groups of transition and post

transition elements are referred to as heavy metals, which include cadmium,

chromium, copper, manganese, nickel, mercury, lead and zinc and the

metalloids arsenic and selenium. Most of these elements are classified as

priority pollutants by the United States Environmental Protection Agency

(USEPA) and have been grouped under dangerous substances by the

Commission of European Communities (CEC) (Athar and Vohra 1995).

These metallic elements are an intrinsic component of the

environment, and a variety of natural processes are responsible for their

widespread occurrence at trace levels in various parts of the biosphere.

Regardless of the source of generation, all heavy metals finally end up in the

surface and groundwater.

So, investigations are needed to device methods, which are

inexpensive, simple, easy to operate and maintain, for the removal of heavy

metals from waste water. Among the commonly used methods, adsorption is

the most effective and widely employed method to treat waste water

containing different heavy metals.

Considerable attention has been devoted to the study of removal of

heavy metals from synthetic waste water by the adsorption phenomenon using

adsorbents under optimum operating conditions.

1.2 SOURCES OF HEAVY METALS

Heavy metal pollution is mainly from five different sources through

which the metals and their ions come into the environment (Manivasakam

1987).

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1. Geological weathering.

2. Industrial processing of ores, metals and metal compounds

3. Use of metal, metal components and compounds.

4. Animal and human excretions which contain heavy metals and

5. Leaching of metals from garbage and solid waste dumps.

Sometimes ground water may have a high concentration of heavy

metals depending on the lithosphere. Domestic waste water also contributes to

heavy metal concentration.

1.3 METHODS FOR THE REMOVAL OF HEAVY METALS

A number of specialized processes have been developed for the

removal of heavy metals from waste water (Manivasakam 1987, Calace et al

2003). These include chemical precipitation, coagulation-flocculation, electro

coagulation, cementation, ion exchange, membrane process, electro-flotation,

concentration, adsorption, absorption, electro-deposition, reverse osmosis,

solvent extraction, ion exchange process, evaporative recovery and biological

treatment.

1.4 ADVANTAGES OF ADSORPTION OVER OTHER METHODS

Conventional treatment technologies such as precipitation and

coagulation are the most widely used methods for removing heavy metals, as

insoluble hydroxide at alkaline pH or sometimes as sulphides. A major

problem with this type of treatment is the disposal of the precipitated

hydroxide (Wang and Chen 2009). These technologies are also less effective

and more expensive when situations involving high volumes but low metal

concentration (typically < 50 mg L-1) are encountered (Salinas et al 2000). Ion

exchange treatment which is the second most widely used method for heavy

metals removal does not appear to be practicable because it is not cost

effective (Ajmal et al 1998).

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Chemical techniques such as ion exchange and solvent extraction

lack sufficiently high affinity and selectivity to reduce residual metal ion to

the level dictated by the government regulation. Techniques such as

membrane process, electrochemical treatment and evaporative recovery are

limited in their use due to their high operational and maintenance cost,

process complexity and low efficiency of heavy metal removal (Kapoor and

Viraraghavan 1995).

Cost effectiveness and adsorption properties are the main criteria

for choosing an adsorption process to remove heavy metals from aqueous

solution. Adsorption process has higher selectivity. Adsorption based

processes offer a more reliable and efficient removal of complex inorganic

and organic metals than many other conventional treatment methods. The

adsorption process achieves higher removal levels in a wide range of solution

conditions and generally reduces the quantity of sludge or solid residuals that

need to be disposed (Smith 1996).

The adsorption phenomenon has still been found to be

economically appealing for the removal of toxic metals from waste water by

choosing adsorbents under optimum operating conditions. Therefore, the

adsorption process is reported to be the best method for removal of metal ion

(Karabulut et al 2000, Cao et al 2010).

1.5 ADSORPTION PROCESS

Adsorption (Slejko 1985, Suzuki 1990, Noll et al 1992) involves

the preferential partitioning of substances from the gaseous or the liquid phase

accompanied by its accumulation or concentration onto the surface of a solid

substrate. The adsorbing phase is the adsorbent, and the material concentrated

or adsorbed at the surface of that phase is the adsorbate.

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1.5.1 Gas Phase Adsorption

This is a condensation process where the adsorption forces

condense the molecules from the bulk phase within the pores of the adsorbent.

The driving force for adsorption is the ratio of the partial pressure and the

vapor pressure of the compound.

1.5.2 Liquid Phase Adsorption

The molecules go from the bulk phase to being adsorbed in the

pores in a semi-liquid state. The driving force for adsorption is the ratio of the

concentration to the solubility of the compound.

1.5.3 Adsorption Mechanisms

Adsorption processes are classified as either physical or chemical.

Physical adsorption occurs when the Vanderwaals forces bind

the adsorbing molecule onto the solid substrate; these intermolecular

forces are the same as the bond molecules to the surface of a liquid. It follows

that heats of adsorption are comparable in magnitude to latent heats (10 to

70 KJ mol-1). Species that are physically adsorbed to a solid can be released

by applying the heat; the process is reversible. An increase in temperature

causes a decrease in adsorption efficiency and capacity.

Chemical adsorption occurs when covalent or ionic bonds are

formed between the adsorbing molecules and the solid substrate. This

bonding leads to a change in the chemical form of the adsorbed compounds,

and is therefore not reversible. The bonding forces for chemical adsorption

are much greater than for physical adsorption. Thus, more heat is liberated.

With chemical adsorption, higher temperatures can improve performance.

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1.6 LITERATURE REVIEW

Major trace elements generally present in various industrial

effluents (Dean et al 1972) are listed in Table 1.1. Sources, drinking water

standards and potential health effects (David and Bela 1997) of some widely

used heavy metals are given in Table 1.2.

Table 1.1 Major trace elements in industrial effluents

S.

No.Industry As Cd Cr Cu Fe Hg Mn Pb Ni Se Sn Zn

1. Paper and pulp - - X X - X - X X - - X

2. Organic chemicals - X X - X X - X - X X X

3. Inorganicchemicals

- X X - X X X - - X X X

4. Fertilisers X X X X X X X X X X - X

5. Petroleum refining - X X X X - - X X - - X

6. Metal finishing - X X X - X - - X X - -

7. Textile millproducts

- - X - - - - - - - - -

8. Leather tanningand finishing

- - X - - - - - - - - -

9. Pesticides X - - - - X - X - X - X

10. Paints and dyes - X X X - X - X - X - -

11. Batteries - X - - - X - X - X - X

12. Electrical andElectronics

- X - X - X - X - X - -

13. Explosives X - - X - X - X - - - -

14. Mining andmetallurgy

X X X X - X - - - X - X

15. Pharmaceuticals X - - - - - - - - - - X

X – Presence of heavy metals in industries.

Source: Trivedy, R.K. “Pollution management in industries”, Environmental Publication,

Karad, India, pp. 170, 1989.

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Table 1.2 Sources, Drinking Water Standards and Potential Health

Effects of Heavy Metals

S.

No.Elements Sources

Max conta -

mination level

(mg L-1

)

Effects

1. Antimony Industry, type setting,enameled ware

0.006Shortens life span, heartdisease.

2. Arsenic Leaching, Weatheringprocess, Volcaniceruption

0.01Dermal pigments, Skinand lung cancer,Vascular diseases.

3. Barium Natural mineraldeposits, Oil/gasdrilling operation,Paints etc.

2.0

Affects circulatorysystems

4. Beryllium Coal combustion,Nuclear power plant,Rocket fuel, Ceramicunit

0.004

Acute and chronicrespiratory diseases, lungcancer, beryllosis.

5. Cadmium Coal combustion,Plating, Phophaticfertilizers, Water pipe,Tobacco smoke etc.

0.005

Cardiovasculardiseases,cancer,hypertension.

6. Chromium Anodising, Coolingtowers, Dye,Electroplating,inks,Paint, Tanning etc.

0.1

Cancer

7. Cobalt Alloys, Steel, Electro -plating,Glass enameletc.

0.05Cancer

8. Copper Paper and pulp,Electrical goods,Utensils, Electronics,Chemicals.

1.0

Cancer(suspected)

9. Iron Steel, Machinery, Dye,Textile, Medicines etc.

0.3Cancer(suspected)

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Table 1.2 (Continued)

S.

No.Elements Sources

Max conta -

mination level

(mg L-1

)

Effects

10. Lead Battery industry, Autoexhausts, Paints etc

0.05

Affects nervous and renalsystem, head ache, braindamage, cancerconvulsion, blue linealong gums.

11. Manganese Metal alloys, Powerplants, Gasoline. 0.05

Nerve damage ( in traceamounts essential tohuman)

12. Mercury Chlo-alkali industry,Coal combustion,Electrical batteries etc

0.002Nerve damage,kidneyand brain damage, death.

13. Nickel Coal, Diesel oil, Metalplating, Steel and nonferrous alloys, Tobaccosmoke etc

0.1

Lung cancer, affectsrespiratory system.

14. Selenium Coal and oilcombustion, Glass andsulphur industry, Paperindustry etc.

0.05

Carcinogenic, causesdental caries (essential toman in trace amounts)

15. Zinc Galvanizing, alloys,rayon, paper industryetc.

5.0Cancer (suspected)

1.6.1 Heavy Metals

Several research studies of heavy metals adsorption onto various

adsorbents have been published. Several adsorbents such as sawdust (Ajmal

et al 1998), silica and iron oxide (Subramaniam et al 2003), sewage sludge

ash (Pan et al 2003), anatase type titanium dioxide (Kim et al 2003), olive

mill residues (Veglio et al 2003), inorganic colloids (Subramaniam and

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Yiocoumi 2001), blast furnace sludge (Lopez et al 1998), functionalized silica

(Bois et al 2003), red mud and fly ashes (Apak et al 1998, Cho et al 2005),

peat (Gosset et al 1986), paper mill sludge (Calace et al 2003), activated

carbon (Goyal et al 2001, Monser and Adhoum 2002), calcined phosphate

(Aklil et al 2004), rice bran (Montanher et al 2005), vermiculite (Malandrino

et al 2006), anaerobic granular biomass (Hawari and Mulligan 2006), tea

waste (Amarasinghe and Williams 2007), poplar wood sawdust (Sciban et al

2007), commercial activated carbon (Srivastava et al 2008), activated carbon

developed from walnut, hazelnut, almond, pistachio shell, and apricot stone

(Kazemipour et al 2008), activated carbon from hazelnut husks (Imamoglu

and Tekir 2008), alumina (Mahmoud et al 2010), chitosan (Wu et al 2010), fly

ash (Ahmaruzzaman 2010) have been used for metal adsorption.

Petrov et al (1992) studied the adsorptive removal of several metal

ions such as Zn, Cd, Pb and Cu from aqueous solution on modifiedanthracite

prepared by thermal oxidation of anthracite in flowing air. The metal uptake

increased with increasing pH of the solution. The uptake was found to be only

slight at solution pH of 1 but it increased considerably in the pH range 3-4.

The oxidation of the carbon enhanced the uptake of the metal ions because of

the creation of oxygen surface groups on the anthracite surface. The presence

of the electrolyte in the solution decreased the uptake of metal ions.

Cheng and Wang (2000) studied the removal of Cu, Zn and Pb

from synthetic waste water using fixed bed granulated activated carbon. They

pretreated the carbon with deionised water and carried out the adsorption of

single-species (Cu, Zn, and Pb) and multi-species (Cu–Zn, Cu–Pb, and Cu–

Pb–Zn) metal ions. It was demonstrated that the breakthrough occurred more

slowly with an increase in the influent pH and a decrease in the flow rate.

Experiments on competitive adsorption illustrated that the removal of metal

ions decreased when additional metal ions were added.

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The use of adsorbent produced by the chemical treatment of locally

available clay for the removal of some heavy metals from waste water has

been investigated by Vengris et al (2001). The modification of natural clay

was achieved by treating it with hydrochloric acid and subsequent

neutralisation of the resultant solution with sodium hydroxide. Acidic

treatment led to the decomposition of the montmorillonite structure. The

uptake capacity of the modified clay for nickel, copper and zinc increased

significantly. Batch and column sorption methods enabled the removal of

nickel, copper and zinc ions till the permissible sewerage discharge

concentration. They found that the breakthrough point at a flow rate of 2 mL

min-1 for copper ions occurred earlier than that for nickel and zinc. Also the

column uptake capacity at 40% breakthrough for nickel and zinc amounted to

1.15 and 0.92 meq g-1, respectively, and 0.75 meq g-1 for copper at 50%

breakthrough. The sorption process was reflected using the Langmuir-type

isotherm. The desorption rate of nickel, copper and zinc by water at pH 5 was

negligible.

Monser and Adhoum (2002) studied the removal of Cu, Zn, Cr and

CN from waste water onto modified activated carbon, which have tetra butyl

ammonium iodide and sodium diethyl dithio carbamate immobilized on their

surface. They found that the tetra butyl ammonium iodide – carbon adsorbent

had effective removal capacity approximately five times that of untreated

carbon. The sodium diethyl dithio carbamate – carbon column had an

effective removal capacity for Cu (4 times), Zn (4 times) and Cr (2 times)

greater than the untreated carbon.

Bayat (2002) compared two different Turkish fly ashes (Afsin-

Elbistan and Seyitomer) for their ability to remove nickel, copper and zinc

from aqueous solutions. The equilibrium time was found to be 2 h for all

metals on both the fly ashes. The maximum metal removal was found to be

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pH 6 for Cu, pH 7 for Zn and pH 8 for Ni. The effectiveness of fly ash as an

adsorbent improved with increasing calcium (CaO) content. The adsorption

data fitted the Langmuir isotherm better than the Freundlich isotherm. He

found that the fly ash with high calcium content (Afsin-Elbistan) was as

effective as a metal adsorbent as activated carbon and, therefore, were good

prospects as adsorbents for these metals.

Wang et al (2006) observed that the fly ash modified by

hydrothermal treatment using NaOH solutions had better adsorbing capacity

for heavy metals and dyes. The XRD profiles revealed a number of new

reflexes, suggesting that a phase transformation had probably occurred. Both

heat treatment and chemical treatment increased the surface area and pore

volume. They found that the removal efficiency for copper and nickel ions

ranged from 30% to 90% depending on the initial concentrations. Also

increased adsorption temperatures enhanced the adsorption efficiency of both

the heavy metals.

Srivastava et al (2008) used activated carbon of commercial grade

for the adsorption of Cd, Ni and Zn, and found the BET surface area to be

171.05 m2 g-1. They found the adsorption to be a gradual process and that the

quasi-equilibrium condition was reached in 5 h. The effective diffusion

coefficient was of the order of 10 12 m2 s-1.

Poplar wood sawdust as a adsorbent was examined by Sciban et al

(2007) for the removal of copper, zinc and cadmium from electroplating

waste water. Langmuir, Freundlich, BET and competitive Langmuir (two

competing ions) isotherms were fitted to the experimental data and the

goodness of fit for adsorption was compared. The shapes of the isotherms

obtained fitted well with the multilayer adsorption. The adsorption of Cu ions

from the mixture (in waste water) was better than that from a single metal

solution. The adsorptions of Zn from waste water and from model water were

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approximately equal, while that of Cd was significantly lower from the waste

water than from the model water. The selectivity of the sawdust for metal ion

adsorption was as follows: Cu > Zn > Cd.

Kazemipour et al (2008) investigated the adsorption of Cu, Zn, Pb,

and Cd that exist in industrial waste water onto the carbon produced from

nutshells of walnut, hazelnut, pistachio, almond, and apricot stone. All the

agricultural shells and stones used were ground, sieved to a defined size

range, and carbonized in an oven. The time and temperature of heating were

optimized at 15 min and 800oC respectively, to reach maximum removal

efficiency. The experiments were carried out using columns filled with a

predetermined amount of the adsorbent. The removal efficiency was

optimized based on the initial pH, flow rate, and dose of adsorbent. They

found that the maximum removal occurred at pH 6–10, flow rate of 3 mL min-1

and 0.1 g of the adsorbent. The adsorption capacity of the carbon decreased

on repeated use. They also studied the efficiency of the carbon to remove the

cations from real waste water produced by copper industries. The findings

showed that the removal efficiencies were much more in real samples.

1.6.2 Nickel, Copper and Zinc

The present work concentrates on the removal of heavy metals such

as copper, nickel and zinc from aqueous solutions and waste waters.

1.6.2.1 Nickel

Nickel may be found in waste water discharges from mining,

electroplating, pigments and ceramic industries, battery and accumulator

manufacturing (Parab et al 2006). Nickel is toxic to a variety of aquatic

organisms, even at very low concentration. An uptake of large quantities of

nickel may lead to higher instances of cancer, lung embolism, respiratory

failure, birth defects, asthma and chronic bronchitis, severe damage to kidney,

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gastrointestinal distress (e.g. nausea, vomiting, diarrhea), allergic reactions

such as skin rashes and heart disorders. Exposure to nickel and its compounds

may result in the development of a dermatitis known as “nickel itch” in

sensitive individuals (USEPA 1986, ATSDR 1997). The properties of nickel

are summarized in Table 1.3.

Table 1.3 Properties of nickel

Properties Values

Atomic number 28

Atomic weight 58.71 g mol-1

Melting point 1453 C

Boiling point 2913 C

Density 8.908 g cm-3 at 20 C, 7.81 g cm-3 at meltingpoint

Electronegativity 1.91 (Pauling); 1.75 (Allred Rochow)

Ionic radius 0.69Å (Ni2+); 0.6Å (Ni3+)

Atomic radius 1.24Å

Covalent radius 1.15Å

Vapour pressure 237 Pa (at melting point)

Thermal conductivity 0.907 W (cm K)-1 (298 K)

Electrical resistivity 6.97x10-6 ohm cm (20 C)

Specific heat 0.44 J (g K)-1 (298 K)

HFusion 17.48 kJ mol-1

HVap 377.5 kJ mol-1

Energy of first ionization 735 kJ mol -1

Energy of second ionization 1753 kJ mol -1

Energy of third ionization 3387 kJ mol -1

The EPA stipulates that nickel in drinking water should not exceed

0.04 mg L-1 (Sheng et al 2004). In India, the acceptable limit of Ni in drinking

water is 0.01 mg L 1 and 2.0 mg L 1 for discharge of industrial waste water.

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(Sharma et al 1992). Maximum contaminant limit for nickel in bottled water

has been fixed as 0.05 mg L-1 by European Economic Community (Demirbas

et al 2002). Hence, it is essential to remove Ni from industrial waste water

before releasing it into natural water sources.

A number of workers have used different adsorbent systems,

developed from various industrial waste materials, for the removal of Ni. Rice

hull (Suemitsu et al 1986), sphagnum peat (Viraraghavan and Drohamraju

1993), peat moss (Lo et al 1995), tea factory waste (Malkoc and Nuhoglu,

2005), blast furnace slag (Dimitrova 1996), apple waste (Maranon and Sastre

1991), peanut hull carbon (Periasamy and Namasivayam 1995), coir pith

activated carbon (Kadirvelu et al 2001), hazelnut shell activated carbon

(Demirbas et al 2002), bagasse fly ash (Gupta et al 2003), clay based beds

(Marquez et al 2004), saw dust (Shukla et al 2005), activated carbon from

waste apricot (Erdogan et al 2005), protonated rice bran (Zafar et al 2007),

Na-modernite (Wang et al 2007) have been investigated to remove Ni from

waste water. They all observed that a decrease in the adsorbent concentration

with constant Ni concentration, or an increase in the Ni concentration with

constant adsorbent concentration resulted in a higher nickel uptake per unit

weight of adsorbent. The effect of other operating variables, viz., solution pH,

temperature, particle size, etc., on the removal of nickel have been studied and

sorption characteristics have been evaluated using Freundlich, Langmuir,

Temkin and Dubinin–Radushkevich (D-R) adsorption isotherms.

Kadirvelu et al (2001) prepared activated carbon from coirpith by

chemical activation for the removal of Ni from aqueous solution. The specific

surface area was found to be 592 m2 g-1. They recovered Ni after adsorption

by treatment with HCl and confirmed the adsorption mechanism to be ion

exchange.

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Gupta et al (2003) studied the removal of nickel from waste water

using bagasse fly ash, an industrial solid waste of the sugar industry. The

maximum adsorption of nickel occurred at a concentration of 12 mg L-1 and

90 % removal of nickel was possible in about 80 min. They found that the

maximum adsorption of nickel occurred at a pH value of 6.5 and the

adsorption data followed the Langmuir model better than the Freundlich

model. They also observed the adsorption process to be endothermic.

Gezici et al (2005) used the sodium form of insolubilized humic

acid as the solid phase in a column. Column operations were performed and

all of them were monitored continuously using a flow through cell-adapted

UV-Vis spectrophotometer. Sorption characteristics were evaluated using the

Freundlich, Langmuir, and Dubinin–Radushkevich (D-R) adsorption

isotherms, as well as by Scatchard plot analysis. The multilayer sorption was

found to be agreeable for Ni. From the D-R isotherm the mean free energy of

sorption (E) was calculated to be 6.65 kJ mol 1.

The potential to remove Ni from aqueous solutions using Na-

mordenite, a common zeolite mineral, was investigated by Wang et al (2007).

The maximum sorption capacity was found to be 5.324 mg g-1 at pH 6, the

initial concentration of 40 mg L-1 at temperature of 20oC. The activation

energy (Ea) was found to be 12.465 kJ mol-1 indicating a chemical sorption

process involving weak interactions between the sorbent and the sorbate.

They also observed that Ni adsorption by the Na-mordenite was not

completely attributed to ion exchange and when compared to other

adsorbents, Ni showed a lower affinity towards the clay mineral adsorbents.

Two Portuguese natural ball-clays named ZA-4 and NC were used

as bed filters by Marquez et al (2004) for the removal of Ni and they

compared the results with that of a commercial grade granular activated

carbon. They found that clay based materials showed higher removal

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efficiency when compared to granular activated carbon (GAC). Higher cation

exchange capacity and development of surface negative charge on the clay

particles in contact with water also contributed to this promising performance,

despite the lower available specific surface area in comparison with granular

activated carbon.

Demirbas et al (2002) carried out the adsorption of Ni using

activated carbon prepared from hazelnut shell. They found that a contact time

of 180 min was required to reach equilibrium. The equilibrium data were

analysed using the Langmuir, Freundlich and Temkin isotherms.

The rice bran in its acid treated (H3PO4) form was used as a low

cost adsorbent for the Ni removal by Zafar et al (2007). The adsorption

characteristics of nickel on protonated rice bran were evaluated as a function

of pH, biosorbent size, biosorbent dosage, initial concentration of nickel and

time. Within the tested pH range (pH 1–7), they found that protonated rice

bran displayed more resistance to pH variation, retaining up to 102 mg g-1 of

the nickel binding capacity at pH 6. Kinetic and isotherm experiments were

carried out at the optimal pH 6. The equilibrium adsorption data fitted better

to the Langmuir adsorption isotherm model. The order of magnitude of the

Go values indicated an ion-exchange physiochemical sorption process.

Erdogan et al (2005) prepared activated carbon from waste apricot

using K2CO3 as the activating agent for Ni adsorption from synthetic waste

water. The activation temperature was varied in the temperature range of 400–

900oC and the N2 atmosphere was used with 10oC/min heat rate. They

observed the maximum surface area (1214 m2 g-1) and the micropore volume

(0.355 cm3 g-1) at 900oC. The adsorption parameters were determined using

the Langmuir model. The optimal conditions were determined to be; pH 5, 0.7

g (10 mL)-1 adsorbent dosage, 10 mg L-1 initial Ni concentration and 60 min

contact time.

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1.6.2.2 Copper

Copper and its compounds are ubiquitous in the environment and

are thus found frequently in surface water. It is also a micronutrient in

agriculture and can, therefore, accumulate in surface waters. Copper bearing

mining wastes and acid mine drainage, discharge significant quantities of

dissolved copper into the waste water. The additional potential sources of

copper bearing waste include electrical apparatus, smelting, metal

electroplating baths, alloy industries, plumbing, roofing and building

construction, gasoline additive, cable covering ammunition, battery industries,

fertilizer industry, paints and pigments, municipal and storm run off

(Buchauer 1973, Dean et al 1972). The excessive intake of copper by man

leads to (WHO 1984) severe irritation of the nose, mouth and eyes, causes

headaches, dizziness, vomiting, diarrhea and widespread capillary damage,

brain damage, hepatic and renal damage and central nervous problems

followed by depression.

Though the maximum permissible concentration by the Indian

Council of Medical Research (ICMR), WHO, USPHS are 3.0 mg L-1, 1.5 mg

L-1 and 1.0 mg L-1 respectively, the maximum recommended concentration of

Cu2+ in drinking water by these agencies is 1.0 mg L-1 (Rao 1992).

Consequently, it is essential that potable waters be given some treatment to

remove copper before domestic use. As copper (Cu2+) is a highly toxic

element, the removal of Cu2+ from waste water has been the subject of many

studies. The properties of copper are summarized in Table 1.4.

Goyal et al (2001), Ajmal et al (1998), Larous et al (2005), Kim et

al (2003), pan et al (2003), Sebe et al (2004), Huang (2007), Subramaniam et

al (2003), Kahn and Khattak (1992), Low et al (1995), Mugisidi et al (2007),

Aman et al (2008), Demirbas et al (2008) studied the removal of Cu by

adsorption using adsorbents such as activated carbons, sawdust, anatase type

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titanium dioxide (photocatalyst), sewage sludge ash, eelgrass, waste iron

oxide, silica and iron oxide, carbon black spheron – 9, coconut husk, modified

activated carbon, potato peel, hazelnut shell etc. They all found that the

percentage adsorption increases with increasing contact time, carbon dosage,

pH, temperature and decreases with an increase in the initial copper

concentration. Most of them used the Langmuir and Freundlich adsorption

isotherm to describe the adsorption process.

Table 1.4 Properties of copper

Properties Values

Atomic number 29


Melting point 1083 C

Boiling point 2595 C

Density 8.95 g cm-3 at 20 C, 7.94 g cm-3 at meltingpoint


Ionic radius 0.96Å (Cu+); 0.73Å (Cu2+); 0.69Å (Cu3+)



Vapour pressure 5.05x10-2 Pa (at melting point)




HFusion 13 kJ mol-1

HVap 306.7 kJ mol-1

Energy of first ionization 743.5 kJ mol -1


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Goyal et al (2001) carried out adsorption studies in the

concentration range of 40 – 1000 mg/l. They found that at pH greater than 6,

the adsorption studies could not be carried out because of the precipitation of

copper hydroxide. Also, the uptake of Cu (II) ions by granulated activated

carbon and activated carbon fibers was influenced by the presence of acidic

surface groups. They found that the increase in adsorption on oxidation

depends on the nature of oxidative treatment while the decrease in adsorption

on degassing depends on the temperature of degassing.

Ajmal et al (1998), while studying the role of sawdust in the

removal of Cu(II) ions from a solution concentration of 17.054 mg (100 mL)-1,

found that the maximum adsorption occurred at pH 6. They observed that

total adsorption decreased with an increase in temperature at low

concentration and a reversal was observed in the adsorption capacity at higher

concentrations where the total adsorption increased with the temperature. The

effect of salinity on the adsorption of Cu was also tested and it was found that

the presence of NaCl in the range of 0.25 – 5.0 g (50 mL)-1 reduced the

adsorption of Cu from 81 to 10 %.

Kim and co-workers (2003) used anatase type titanium dioxide

photocatalyst particles for the adsorption of Cu (II) from an aqueous solution

of concentration 10 mg L-1. They observed that the pH value of the solution

changed to acidic pH during adsorption. The adsorption rate was rapid with

an increasing number of UV lamps of 254 nm.

Pan et al (2003), while studying the removal of Cu (II) ions from

waste water using Sewage Sludge Ash (SSA) observed that the chemical

composition of SSA was similar to that of fly ash. The precipitation of copper

hydroxide occurred when the equilibrium pH of waste water was above 6.2

and this observation was in agreement with the findings of Gilles Sebe et al

(2004).

20

Huang et al (2007) used waste iron oxide as a low cost adsorbent

for the treatment of waste water containing copper. XRD and SEM were used

to characterize the iron oxide material. The adsorption capacity was found to

be 0.21 mmol g 1 for 0.8 mmol dm 3 initial Cu2+ concentrations at pH 6.0 and

300 K. They observed that the adsorption data were well described by the

Freundlich model and the adsorption process to be endothermic.

Kahn and Khattak (1992) studied the removal of Cu(II) from

CuSO4 solution on carbon black spheron – 9 and observed that the adsorption

equilibrium was established within 1 h in the concentration range of

10 – 1000 ppm. The data was found to obey Langmuir and Freundlich

adsorption isotherms except for adsorption at higher pH values where

precipitation was thought to take place. The removal of Cu, Pb and Zn from

aqueous solutions by synthetic geolite was measured as a function of pH at

several temperatures. It was found that the adsorption was closely related to

cation hydrolysis.

Low et al (1995) examined the ability of coconut husk and its

reactive dye coated forms for the removal of copper from aqueous solution

and found that the dye coating of the husk enhanced the removal of copper.

They also found that the Langmuir isotherm fitted the equilibrium data for

both natural and dye-coated husk-Cu systems.

Mugisidi et al (2007) modified the activated carbon from coconut

shell using sodium acetate at concentrations of 10 % and 15 %, and used it in

a fixed-bed column to study the adsorption of copper ions. Synthetic waste

water containing 258 mg L-1 of Cu was passed through plain activated carbon

and modified activated carbon. The highest adsorption capacity was found for

the activated carbon modified by treatment with 15% sodium acetate, which

adsorbed 45 mg of Cu; that is 2.2 times as much as the untreated activated

carbon. After regeneration with 0.71M NaOH, they found that the activated

21

carbon modified by treatment with 15% sodium acetate was able to adsorb

60 mg of Cu; that is three times as much as the untreated activated carbon.

Aman et al (2008) used potato peels for the removal of Cu from

waste water. The optimum pH for adsorption onto potato peels charcoal was

found to be 6.0. They also observed that the rejuvenated material retained its

efficiency to adsorb copper during 5 repeated cycles.

Demirbas et al (2008) carried out the removal of copper from

aqueous solution and found that the surface of hazelnut shell exhibits negative

zeta potential value at all studied pH values. They also observed that the

hazelnut shell had no isoelectrical point in the studied pH range and the

adsorption was endothermic.

1.6.2.3 Zinc

Zinc is present in air, soil, water, and in almost all types of food.

Zinc is naturally released into the environment; however industrial activities

are mostly responsible for zinc pollution. Elevated levels of zinc come from a

variety of sources like mining and foundry activities, zinc, lead, and cadmium

refining, steel production, carbon combustion, and solid waste incineration.

Zinc is commonly used to coat iron and other metals for the prevention of

oxidation. Various zinc salts are industrially used in wood preservatives,

catalysts, photographic paper, accelerators for rubber vulcanization, ceramics,

textiles, fertilizers, pigments, and batteries (USDHHS, 1993). Water

reservoirs are contaminated by the run-off from these industries. Other

sources of metallic zinc traces in drinking water are water treatment processes

and pick-up of metallic ions during storage/distribution. The properties of

zinc are summarized in Table 1.5.

22

Table 1.5 Properties of zinc

Properties Values

Atomic number 30


Melting point 419.5 C

Boiling point 907 C

Density 7.11 g cm-3 at 20 C


Ionic radius 0.74Å (Zn2+)



Vapour pressure 19.2 Pa (at melting point)




HFusion 7.28 kJ mol-1

HVap 114.2 kJ mol-1

Energy of first ionization 904.5 kJ mol -1


Energy of third ionization 3831 kJ mol -1

Zinc is not biodegradable and travels through the food chain via

bioaccumulation. Zinc causes various health problems, such as stomach

cramps, skin irritations, vomiting, nausea, anaemia, accumulative poisoning,

cancer, brain damage, etc. (Burrell 1974, Berman 1980). Very high levels of

zinc can damage the pancreas and disturb the protein metabolism thereby

causing arteriosclerosis. Extensive exposure to zinc chloride can cause

respiratory disorders. According to few surveys from the public health

services of different countries, a significant number of people have been

23

exposed to the hazards of excess metals in the municipal water supplies

(WHO 1971). Therefore, there is significant interest regarding zinc removal

from waste waters and its toxicity for humans at levels of 100–500mg (day)-1.

World Health Organization (WHO) recommends the maximum acceptable

concentration of zinc in drinking water as 5.0 mg L-1 (Kumar et al 2006).

Agrawal et al (2004) studied the removal of zinc from aqueous

solutions using sea nodule residue, a solid waste generated during the

processing of polymetallic sea nodules for copper, nickel, and cobalt

recovery. About 2.0 g of SNR was found to be sufficient to remove 99.8% of

200 mg L 1 zinc from 100 mL aqueous solution in 4 h, and the optimum pH

value for maximum adsorption was found to be 5.5. They also found the

adsorption of Zn to be an endothermic process and low value of the activation

energy indicated the adsorption to be physical in nature.

The factors affecting adsorption characteristics of Zn2+ on two

natural zeolites (Gordes and Bigadic zeolites) were investigated by Oren and

Kaya (2006). The results showed that the Zn2+ adsorption behavior of both

zeolites were highly dependent on the pH. The pH experiments showed that

the governing factors affecting the adsorption characteristics of all materials

was the competition of the H+ ions with Zn2+ ions (under pH 4), ion exchange

(pH 4–6), participation of zinc hydroxyl species in the adsorption and

precipitation onto the zeolite structure (pH 6–8). The results also revealed that

an increase in the initial concentration of Zn2+ in the system increased the

adsorption capacity to a degree, then it became constant at higher

concentrations. They found that the removal efficiency of Gordes zeolite was

two times higher than that of Bigadic zeolite.

Kaya and Oren (2005) carried out the adsorption of zinc from

aqueous solutions onto bentonite and found that the adsorption characteristics

of zeolites for zinc ions were very limited when compared with the natural

24

and Na-enriched bentonites. Previous investigations on bentonites showed

that the maximum adsorption capacity of Na-enriched bentonite and natural

bentonite was 54 and 24 mg g-1, respectively. Considering the zeolites, it was

6 and 3 mg g-1 for Gordes and Bigadic. The lower adsorption rates for zeolites

with respect to bentonites may be due to the difficulty in the penetration of

hydrated zinc ions into the zeolite channels. Hence, they concluded that the

adsorption may take place on the zeolite surface.

Amuda et al (2007) modified the activated carbon prepared from

coconut shell with chitosan and/or oxidizing agent (phosphoric acid) to

produce a composite adsorbent for the removal of zinc from industrial waste

water. Operational parameters such as pH, agitation time and adsorbent

concentration, initial ion concentration and particle size were also studied.

They observed that the Langmuir isotherm represented the experimental data

better than the Freundlich isotherm thus indicating the monolayer coverage of

the zinc (II) on the surface of the adsorbent. Desorption studies were carried

out with NaOH and substantial recovery of the metal was evident. It was also

suggested that the dominant sorption mechanism was ion exchange.

The dependence of Zn removal from aqueous solutions by mixed

mineral systems of kaolinite, montmorillonite, and goethite on surface charge,

surface chemistry, and the kinetic pattern of the sorbing ions over time was

investigated by Egirani et al (2005). Using an empirical model, they found

that the mineral mixing reduced the exchange of protons for adsorbing ions

and the acidity of the reactive sites, thus impeding Zn removal by proton

exchange. Based on the amount of Zn adsorbed on the mixed mineral

suspensions at ionic strength 0.01 to 0.1 M and pH 4, they suggested that Zn

removal from aqueous solution was both by inner and outer sphere

complexation. The behavior of the mixed suspensions in Zn sorption

25

suggested that different reactive sites were involved at the onset of sorption,

becoming similar to those of the single mineral components over time.

Janssen et al (2003) found that clay–Al hydroxide polymers could

bind heavy metals effectively, and played an important role in the adsorption

behavior and metal binding capacity of soils.

1.6.3 Adsorbents

Adsorbents (Noll et al 1992, Oscik et al 1982) are porous materials

that contain many miniscule internal pores. The most common industrial

adsorbents are activated carbon, silica gel, and activated alumina, because

they present enormous surface areas per unit weight. Activated carbon is

produced by roasting organic material to decompose it to granules of carbon -

coconut shell, sawdust, wood, and bone are some of the common sources.

Typical surface areas are 300 to 1500 m2 g-1. Silica gel is a matrix of

hydrated silicon dioxide. Silica is used to separate hydrocarbons. Typical

surface areas are 300 to 900 m2 g-1. Activated alumina is commonly used to

remove oxygenates and mercaptans from hydrocarbons and fluorides from

water. Typical surface areas are 200 to 400 m2 g-1. The adsorbents such as

zeolite, carbon molecular sieve, bone char, iron and manganese coated sand,

kaolinite clay, hydrated ferric oxide, activated bauxite, titanium oxide,

silicium oxide and other synthetic media are also widely used.

In the last few years many studies have focused on identifying

inexpensive but effective adsorbent material (Calace et al 2003, Kornold et al

1996, Davila et al 1992). It is quite well known that activated carbon can be

used and as a matter of fact, is recommended by the USEPA as the best

available technology to remove contaminants from water by adsorption

effectively (Gharaibeh et al 1998). Table 1.6 gives a comparison of the

26

adsorption capacity of Ni, Cu and Zn on different adsorbents taken from the

literature.

Table 1.6 Comparison of adsorption capacity of various adsorbents for

Ni, Cu and Zn

Adsorption Capacity

(mg g-1

)Adsorbent

Ni Cu Zn

Reference

A.C from apricot (AT 400oC) 17.04 - - Erdogan et al (2005)






Hazelnut husk A.C. (20oC) 5.757 - - Demirbas et al (2002)




Coirpith carbon 62.5 - - Kadirvelu et al (2001)

Peanut hull carbon 53.65 - - Periasamy andNamasivayam (1995)

Granular activated carbon 1.49 - - Periasamy andNamasivayam (1995)

Hazelnut husk A.C. - 6.645 - Imamoglu and Tekir(2008)

Spent activated clay - 10.9 - Weng et al (2007)

Activated poplar sawdust - 9.24 - Acar and Eren (2006)

Rubber wood sawdust A.C. - 5.729 - Kalavathy et al (2005)

Activated carbon - 3.56 - Machida et al (2005)

Activated carbon from sugarbeet pulp (AT 300 C)

- 68.03 - Ozer and Tumen(2003)





27

Table 1.6 (Continued)

Adsorption Capacity

(mg g-1

)Adsorbent

Ni Cu Zn

Reference

Activated carbon - 31.11 - Mohan and Singh(2002)

Rice hulls activated carbon - 3.92 - Teker et al (1999)

Carbon prepared from apricotstones

- 12.01 13.21 Budinova et al (1994)

Carbon prepared fromcoconut shells

- 11.10 - Budinova et al (1994)

Carbon prepared from lignitecoal

- 9.80 - Budinova et al (1994)

Carbon prepared from peanuthulls

- 89.29 - Periasamy andNamasivayam (1994)

Commercial activated carbon,India

- 2.74 - Periasamy andNamasivayam (1994)

Acid-treated coconut

shell carbon (ACSC)

- - 45.14 Amuda et al (2007)

Chitosan coated coconut shellcarbon (CCSC)

- - 50.93 Amuda et al (2007)

Chitosan coated ACSC

(CACSC)

- - 60.41 Amuda et al (2007)

Calcined phosphate - - 23.7 Aklil et al (2004)

Red mud - - 12.59 Lopez et al (1998)

Peat - - 9.28 McKay et al (1998)

Blast furnace slag - - 17.65 Gupta et al (1997)

Lignite - - 22.83 Allen and Brown(1995)

1.6.3.1 Activated carbon

Activated carbon (Noll et al 1992, David and Cooney 1987) is a

carbonaceous material which possesses a highly developed porosity, and hence a

large internal surface area. As a result of this, it is commonly used in a wide range

28

of applications, concerned principally with the removal of chemical species

by adsorption from the liquid or gas phase (Bansal et al 1988). Commercial

activated carbon has an internal surface area ranging from 500 to 1500 m2 g-1.

Related to the type of application, two major product groups exist:

Powdered activated carbon; particle size 1-150 micron

Granular activated carbon (granulated or extruded), particle size

in the 0.5-4 mm range

Activated carbon (AC) can be produced by heat treatment, or

“activation”, of raw materials such as wood, coal, peat and coconuts. During

the activation process, the unique internal pore structure is created, and it is

this pore structure, which provides activated carbon its outstanding adsorptive

properties.

Activated carbons have a number of unique characteristics: a large

internal surface area, dedicated (surface) chemical properties and good

accessibility of internal pores. According to IUPAC definitions three groups

of pores can be identified:

Macropores (above 50 nm diameter)

Mesopores (2-50 nm diameter)

Micropores (under 2 nm diameter)

Micropores generally contribute to a major part of the internal

surface area. Macro- and mesopores can generally be regarded as the

highways into the carbon particle, and are crucial for kinetics. The desired

pore structure of an activated carbon product is attained by combining the

right raw material and activation conditions.

29

1.6.3.2 Industrial applications

Activated carbon, finds numerous applications: decolourisation of

sugar and sweeteners, drinking water treatment, gold recovery, production of

pharmaceuticals and fine chemicals, catalytic processes, off gas treatment of

waste incinerators, automotive vapor filters, colour/odour correction in wines

and fruit juices, additive in liquorice, etc.

Activated carbon, because of its large surface area, a microporous

structure and a high degree of surface reactivity, has been considered to be

very good adsorbent for the adsorption of organics and inorganics from waste

water. It is found to be a better adsorbent for metal removal compared to

fuller’s earth or betonite. Fuller’s earth or betonite adsorbents are only

moderately effective at pH greater than 8 (Goyal et al 2001). Thus, a

considerable amount of work is being carried out for the removal of copper

ion from the aqueous phase using activated carbon.

1.6.4 Preparation of Activated Carbon

Activated carbon is one of the most widely used adsorbents. Over

the last few decades, adsorption systems involving activated carbon have

gained importance in the purification and separation processes on a large

scale. The high adsorptive capacities of AC are associated with their internal

porosity and related to properties such as surface area, pore volume and pore

size distribution. As is well known, the type of raw material employed and the

method of preparation dictate the type of porosity and chemical composition

of AC (Girgis et al 2002, Savova et al 2001). The characteristics of activated

carbon and adsorption capacity of AC depend on the physical and chemical

properties of the precursor as well as the activation method (Mattson and

Marck 1971). There are two methods of preparing activated carbon: physical

activation and chemical activation.

30

1.6.4.1 Physical activation

Physical activation (Smisek and Cerny 1970, Jankowska 1991)

involves two different and separate stages: pyrolysis or carbonization of the

precursor and controlled gasification of the resulting char. Carbonization is

the removal of the non-carbon species and the production of a mass of fixed

carbon (char) with a rudimentary porous structure. Experimental conditions of

carbonization (which is carried out in rotary kilns or multiple hearth

furnaces), especially the heating rate, the final temperature, and the residence

time, control the yield of the process but do not have much influence on the

porous texture of the char. As a result of the decomposition and deposition of

tar, the pores become partially filled or blocked by disorganized carbon. This

results in low adsorption capacity which has to be enhanced by activation via

partial controlled gasification with steam, carbon dioxide, or mixtures of the

two.

The development of porosity in a given char activated by steam or

carbon dioxide is different. In the first stages of the activation process, the

burning out of disorganized carbon results in the opening of the partially

blocked pores of the char and a subsequent increase in the micropore volume,

with no large differences between the two activating agents, although

somewhat larger development of mesoporosity occurs with steam. As the

degree of activation increases the differences in porosity created by the

activating agents become more pronounced and it is generally admitted that

carbon dioxide mainly develops the microporosity and that steam produces a

wider pore size distribution, with development of meso- and macroporosity.

There is an important point to be noted with respect to the porosity

development during physical activation of a char. The volume for the

different ranges of porosity may increase with increasing gasification up to

very large levels of burn-off, but the industrial production of activated carbon

31

is dominated by a compromise between porosity development and process

yield.

1.6.4.2 Chemical activation

Several activating agents have been reported for chemical

activation process; however the most important and commonly used

activating agents are phosphoric acid, zinc chloride and alkaline metal

compounds. Phosphoric acid and zinc chloride are used for the activation of

lignocellulosic materials, which have not been carbonized previously,

whereas, metal compounds such as potassium hydroxide are used for

activation of coal precursors or chars. The finely ground lignocellulosic

material is impregnated with a concentrated solution of a dehydrating

chemical, typically phosphoric acid or zinc chloride, to produce degradation

of the cellulosic material. The mixture is dried and heat treated at 400 -

700°C. These chemical agents may promote the formation of cross-links,

leading to the formation of a rigid matrix that is further less prone to volatile

loss and volume contraction upon heating to high temperatures (Wigmans

1989, Jagtoyen 1992). That is, these chemicals favor dehydration prior to

degradation and subsequent repolymerization, reducing the formation of tars

and other volatile products thus increasing the carbon yield. The product is

washed thoroughly to remove the remaining chemical from the carbon, dried,

and classified into the size range required. Carbon yields of 30-50 wt.% can

be obtained when using lignocellulosic materials, very high in comparison to

physical activation of the same precursor (the yield of carbonization is 25-30

wt.%, and assuming a 40% burn off upon gasification the overall yield would

be 15-18 wt.%).

32

1.6.4.3 Combination of chemical and physical activation

A combination of chemical and physical activation can be used to

prepare granular activated carbons with a very high surface area and porosity

adequate for certain specific applications such as gasoline vapor control, gas

storage, etc. Activated carbons of this type have been reported using

lignocellulosic precursors (e.g., olive or peach pits) chemically activated with

phosphoric acid or zinc chloride and later activated under a flow of carbon

dioxide. Uniform, medium-size microporosity and surface areas above 3600

m2 g-1 are obtained with this mixed procedure (Bansal 1988).

1.6.4.4 Advantages of chemical activation over physical activation

The advantage of chemical activation over physical activation is

that it can be performed in a single step and at relatively low temperatures

(usually < 500oC for activation of wood by phosphoric acid (Bansal et al

1988) and between 600 and 700oC for activation of lignocellulosic materials

impregnated with ZnCl2 (Reinoso and Sabio 1992)). The carbonization step

generates the porosity, which becomes accessible when the chemical is

removed by washing (Caturla et al 1991, Sabio et al 1995). Consequently, the

modification of the chemical/precursor ratio permits the adjustment of the

porosity in the final activated carbon. However, the most important

disadvantage of chemical activation is the incorporation of impurities, coming

from the activating agent, which may affect the chemical properties of the

activated carbon. Another disadvantage is the investment needed for the unit

for recovering the chemical used for impregnation.

1.6.4.5 Advantages of phosphoric acid over zinc chloride

The classical chemical used on a large scale for chemical activation

was zinc chloride due to its efficiency and simplicity of the process. However,

33

its use is on the decline, because of the problems of corrosion, ineffective

chemical recovery, and environmental disadvantages associated with zinc

chloride. This process produces activated carbons with large porosity,

although the pore size distribution is determined-for a given precursor-mainly

by the degree of impregnation (the larger the degree of impregnation, the

larger the average pore size of the final carbon). The AC obtained using zinc

chloride however cannot be used in pharmaceutical and food industries as it

may contaminate the products. Since then there have been many studies

reporting the activation of carbon using phosphoric acid.

Because of the disadvantages associated with zinc chloride,

phosphoric acid is used largely in industry to impregnate lignocellulosic

materials, mainly wood. Also, phosphoric acid induces important changes in

the pyrolytic decomposition of the lignocellulosic materials since it promotes

depolymerization, dehydration and redistribution of constituent biopolymers

(Jagtoyen and Derbyshire 1993), favoring the conversion of aliphatic to

aromatic compounds at temperatures lower than when heating in the absence

of an additive, thus increasing the yield. One of the reasons why activation

with phosphoric acid has become popular is because of the improvements

introduced in the process of acid recovery.

1.6.4.6 A review on activated carbon preparation

Several coals (Ehrburger et al 1986, Ahmadpour and Do 1996,

Teng et al 1998, Castello et al 2001), polymers (Park and Jung 2002, Puziy et

al 2002), and some agricultural by-products and forest wastes (Savova et al

2001, Garc a et al 2003, Villegas et al 1993) have been used as raw materials

to prepare AC.

Several studies of chemical activation have been conducted with

ZnCl2, which has been found to maximize the adsorptive capacity and bulk

34

density of activated carbons produced from cellulosic and lignocellulosic

materials (Reinoso and Sabio 1992, Caturla et al 1991, Kandiyoti et al 1984,

Teng and Yeh 1998).

Phosphoric acid activation has been used for a wide variety of

cellulosic precursors such as coconut shells (Laine et al., 1989), white oak

(Jagtoyen and Derbyshire 1993), peach stones (Sabio et al 1996), nut shells

(Toles et al 1998), cotton stalks (Girgis and Ishak 1999), almond shells (Bevia

et al 1984, Toles et al 2000), pecan shells (Dastgheib and Rockstraw 2001),

Arundo donax cane (Vernerson et al 2002), apple pulp (Garcia et al 2002),

peanut hull (Girgis et al 2002) and sugarcane begasse (Girgis et al 1994,

Ahmedna et al 2000).

Activated carbon from cheap and readily available sources such as

coal, coke, peat (Gosset et al 1986), heat treated sulphurised activated carbon

(Gomez et al 1998), sugarcane begasse pith (Krishnan and Anirudhan 2002),

renewable biosource (Basso et al 2002), rice husk (Kalderis et al 2008) have

been successively employed for removal of heavy metals.

A number of activation procedures have been reported in the

literature using phosphoric acid as an activating agent. To name a few, Corral

et al (2006) prepared powder activated carbon (AC) from vine shoots by the

method of chemical activation with phosphoric acid. After size reduction,

vine shoots were impregnated for 2 h with 60 wt % H3PO4 solution at room

temperature, 50 oC and 85oC. The three impregnated products were carbonised

at 400oC for 2h. The carbons were texturally characterised by gas adsorption

(N2, -196oC), mercury porosimetry, and density measurements. Better

developments of surface area and microporosity are obtained when the

impregnation of vine shoots with the H3PO4 solution is effected at 50oC and

for the products heated isothermally at 200 oC and 450oC.

35

Chestnut wood was used in the preparation of activated carbon

using the method of phosphoric acid-chemical activation by Gomez et al

(2005). The influence of heat treatment temperature (i.e., 300, 400, 500 and

600oC) and concentration of the solution of phosphoric acid (i.e., 1:1, 1:2 and

1:3 water/H3PO4 proportions) used in the impregnation of chestnut wood on

textural properties and fractal dimension were studied. The products obtained

were characterized by N2 adsorption at -196oC. The micropore volume (Vmi)

and the specific surface area (SBET) were found to increase with an increase in

temperature and acid concentration. However, Vmi and SBET decreased at

600oC with regard to 500oC. The micropore size distribution was similar in

the products prepared at 400 and 500oC, regardless of the acid concentration.

Activated carbons (ACs) have been prepared using chestnut, cedar

and walnut wood shavings from the furniture industry using phosphoric acid

(H3PO4) at different concentrations (i.e. 36 and 85 wt.%) as the activating

agent (Diez et al 2004). ACs have been characterized by N2 adsorption at 77 K.

Moreover, the fractal dimension have been calculated in order to determine

the AC surface roughness degree. The optimal textural properties of AC have

been obtained by chemical activation with H3PO4 36 wt %.

Guo and Rockstraw (2007) produced AC from rice hull by a one-

step phosphoric acid activation. The pore structure and surface chemistry in

the activation temperature range of 170–450oC was investigated and the

results showed that the development of porosity (extent of activation) was

negligible at activation temperatures below 300oC, and rapid evolution of

pores occurred at temperatures between 300 – 400oC. Porous activated carbon

with bimodel pore structure (pore < 1 nm and pore > 1 nm) and BET surface

area as high as 1295 m2 g-1 were obtained at 450oC. FTIR (Fourier transform

infrared spectroscopy) results revealed the existence of carbonyl-containing,

phosphorus-containing groups, and groups containing Si–O bond. Boehm

36

titration and FTIR results indicate that the surfaces of these carbons contain

both temperature-sensitive and temperature-insensitive groups.

However, there are only few publications reporting the preparation

of activated carbon from Hevea brasiliensis sawdust (Rubber wood saw dust),

Agave sisalana fiber (Sisal fiber) and Moringa oleifera wood (Drumstick

wood) using phosphoric acid as activating agent. One can design activated

carbon for adsorption of specific adsorbate, using approximate precursor and

by optimizing the activation process conditions.

Cost effectiveness, cheap availability, higher metal loading

capacity, relatively high surface area and high binding affinity were the main

criteria for choosing ACs to remove heavy metals from an aqueous solution.

Taking these criteria into consideration, the present study was carried out to

determine the feasibility of using the relatively common, cheap and thrown

away waste Hevea brasiliensis (Rubber wood) saw dust (HBSD), Agave

sisalina (Sisal) fiber (ASF) and Moringa oliefera (Drumstick) wood (MOW)

to prepare highly effective activated carbon with a large surface area. These

carbons were prepared using phosphoric acid as the impregnating agent by

chemical activation method followed by their characterization, for the

adsorption of nickel, copper and zinc from aqueous solutions and effluent, the

studies being carried out in both batch and continuous mode.

1.7 SCOPE OF THE PRESENT STUDY

Any carbonaceous material which is activated either chemically

or physically yields materials which are highly porous and having large

surface area, they are called activated carbon. Commercially available

activated carbons are expensive and hence are not often viable for treatment

of industrial effluents. In the present study it was therefore desired that

alternative raw materials be chosen that are region specific, easily available,

37

inexpensive and without much commercial applications. Activated carbons

prepared using phosphoric acid as the activating reagent was considered for

the removal of heavy metals from aqueous solutions and industrial effluent.

Heavy metals due to their high toxicity and carcinogenic effects need to be

removed from the effluent stream and if possible recovered for further use. In

the present study nickel, copper and zinc were the heavy metals identified for

adsorption on to activated carbons prepared from Hevea brasiliensis sawdust,

Agave sisalana fiber and Moringa oleifera wood. Batch and column studies

were carried out in order to examine the potential of these adsorbents for

adsorption of metal ions from solution. Effluent from electroplating industry

containing nickel ions was also treated using the above activated carbons.

1.8 OBJECTIVE OF THE PRESENT STUDY

In recent years heavy metal removal using adsorption process has

gained momentum as a means for reducing treatment costs.

The objective of the present work is to

Identify the prospects of using low cost substance as raw

materials for the production of adsorbents for removing heavy

metals such as copper, nickel, and zinc from waste water.

Produce activated carbon from Hevea brasiliensis sawdust

(HBSD), Agave sisalana fiber (ASF) and Moringa oleifera

wood (MOW) by chemical activation method using phosphoric

acid as activating agent.

Characterize activated carbon by means of iodine number,

methylene Blue number, methyl violet number, surface area,

yield, TGA analysis, SEM photographs etc.

38

Assess the precision and reproducibility of activated carbon.

Conduct the adsorption process for removing nickel, copper and

zinc from synthetic waste water onto activated carbon produced

from HBSD, ASF and MOW.

Obtain the kinetic data and equilibrium data in batch system by

studying the effects of different experimental parameters such

as agitation time, initial concentration of metal ions, the dosage

of activated carbon, temperature and pH on the adsorption

capacity.

Conduct column experiments to understand the adsorption

behavior in fixed bed column.

Recover the adsorbed metals from adsorbent and to regenerate

the adsorbent

Study the reusability of the regenerated adsorbent and also

sorption performance on repeated usage.

Documents

CHAPTER 1 INTRODUCTION - Shodhgangashodhganga.inflibnet.ac.in/bitstream/10603/9979/6/06_chapter 1.pdf · choosing adsorbents under optimum operating conditions. Therefore, the adsorption