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DOKUZ EYLÜL UNIVERSITY
GRADUATE SCHOOL OF NATURAL AND APPLIED
SCIENCIES
REMOVAL OF HEAVY METALS FROM INDUSTRIAL SLUDGE
by
Işıl AKSAKAL
February, 2005
İZMİR
REMOVAL OF HEAVY METALS FROM INDUSTRIAL SLUDGE
A Thesis Submitted to the
Graduate of Natural and Applied Sciences of Dokuz Eylül University
In Partial Fulfillment of the Requirement for the Degree of Master of Science in
Environmental Engineering, Environmental Technology Program
by
Işıl AKSAKAL
February, 2005
İZMİR
ii
M.Sc THESIS EXAMINATION RESULT FORM
We have read the thesis entitled “REMOVAL OF HEAVY METALS FROM
INDUSTRIAL SLUDGE” completed by IŞIL AKSAKAL under supervision of
Instructor Dr. NURDAN BÜYÜKKAMACI and we certify that in our opinion it is
fully adequate, in scope and in quality, as a thesis for the degree of Master of Science.
Supervisor
(Jury Member) (Jury Member)
Prof.Dr. Cahit HELVACI Director
Graduate School of Natural and Applied Sciences
iii
ACKNOWLEDGMENTS
I would like to express my gratitude to my supervisor Instructor Dr. Nurdan
Büyükkamacı for her guidance and motivation.
I also would like to thank Prof. Dr. Ayşe Filibeli, Instructor Dr. Zihni Yılmaz,
Res. Ass. Azize Ayol and Nazlı Baldan for their valuable helps in my thesis.
I am very grateful to the personnel of wastewater treatment plant of Atatürk
Organized Industrial District, Sahan Dyestuff Industry, Norm Cıvata and Cevher
Döküm for their assistance during taking samples for this study. Also, I thank to the
personnel of DEÜ Wastewater Laboratory for their assistance during my
experiments.
I am particularly grateful to Özgür Aksakal and Sibel Şen, my husband and my
sister for their helps and morale motivations.
Finally, I thank to my father, Erol Şen, and my mother, Habibe Şen, for their
moral support, and patience during my education.
Işıl AKSAKAL
iv
REMOVAL OF HEAVY METALS FROM INDUSTRIAL SLUDGE
ABSTRACT
In this thesis, solid-to-liquid extraction method at lab scale conditions was used
for removal of heavy metals from industrial sludge and the effect of inorganic acid
and organic acid addition was compared. For this purpose, inorganic acid
(HF+HClO4) and organic acids (citric acid, oxalic acid, and acetic acid) were directly
added to sludge samples as an extraction reagent. Three different extraction reagent
concentrations (1 mol, 2 mol, and 5 mol) in organic acid applications were used. In
order to evaluate the effects of extraction time on extraction efficiency, four different
extraction time (1 h, 3 h, 24 h, and 72 h) were examined.
The heavy metal extraction studies were carried out using four different industrial
sludges, which were taken from a dyestuff industry, two metal industries, and an
organized industrial district. The extraction efficiencies were determined depending
on the concentration of extracting reagent and extraction time. The most effective
extraction reagent was determined for each heavy metal of each sludge sample. In
the case of one of the organic acid was the most effective reagent, the most effective
extraction time was also determined.
Keywords: Sludge, heavy metal, extraction
v
ENDÜSTRİYEL ÇAMURLARDAN AĞIR METAL GİDERİMİ
ÖZET
Bu tez kapsamında, endüstriyel çamurlardan ağır metal giderimi laboratuvar
koşullarında incelenmiştir. Bu amaçla katı-sıvı ekstraksiyon metodu kullanılmış ve
inorganik ve organik asit ilavesinin etkisi karşılaştırılmıştır. Deneysel çalışmalarda
ekstraksiyon ayıracı olarak inorganik asit (HF+HClO4) ve organik asitlerin (sitrik
asit,oksalik asit ve asetik asit) etkisi incelenmiştir. Organik asitlerle yapılan
çalışmalarda asit konsantrasyonun etkisinin belirlenebilmesi amacıyla üç farklı
konsantrasyonda asit ilavesi (1 mol, 2 mol ve 5 mol ) ile çalışılmış ve ekstraksiyon
süresinin ağır metal giderim verimi üzerine etkisini değerlendirmek için de dört farklı
ekstraksiyon süresi (1 saat, 3 saat, 24 saat ve 72 saat) uygulanmıştır.
Farklı endüstriyel nitelikli çamurlarda metal ekstraksiyon veriminin
incelenebilmesi için boya endüstrisi, organize sanayi bölgesi ve iki farklı metal
endüstrisine ait atıksu arıtma tesisinden alınan dört farklı endüstriyel çamur ile
çalışılmıştır. Her bir çamur örneğinde bulunan her bir ağır metal için en etkili
ekstraksiyon ayıracı belirlenmiştir. Organik asitlerden birinin inorganik aside göre
daha etkili sonuç vermesi durumunda ise, en etkili ekstraksiyon ayıracı
konsantrasyonu ve en etkili ekstraksiyon süresi tespit edilmiştir.
Anahtar Kelimeler: çamur, ağır metal, ekstraksiyon
vi
CONTENTS
Page
THESIS EXAMINATION RESULT FORM……………………………………………ii
ACKNOWLEDGEMENTS……………………………………………………………..iii
ABSTRACT……………………………………………………………………………..iv
ÖZET……………………………………………………………………………………..v
CHAPTER ONE – INTRODUCTION………………………………………………...1
1. Introduction………………………………………………………………………...1
CHAPTER TWO – GENERATION AND NATURE OF SLUDGE………………...3
2. Generation and Nature of Sludge…………………………………………………..3
2.1 Introduction…………………………………………………………………....3
2.1.1 Sludge Sources…………………………………………………………...3
2.1.2 Sludge Handling and Disposal Methods………………………………....6
2.1.3 Ultimate Disposal and Fertilizer Value of Sludge………………………..9
2.2 Industrial Sludge……………………………………………………………...11
CHAPTER THREE – HEAVY METAL EXTRACTION………………………….14
3. Heavy Metal Extraction…………………………………………………………...14
3.1 Chemistry of Heavy Metals…………………………………………………..14
3.2 Removal Methods of Heavy Metals from Solid Wastes……………………..16
3.2.1 Solid-to-Liquid Extraction………………………………………………17
3.2.2 Physical Separation Processes…………………………………………..20
3.3 Extraction from Sludge……………………………………………………….23
3.3.1 Extraction Reagents……………………………………………………..25
3.3.1.1 Organic Acids……………………………………………………...26
3.3.1.2 Standard Methods………………………………………………….29
3.3.1.3 Sequential Extraction Method……………………………………..29
vii
3.3.1.4 Summary of Case Studies………………………………………….30
3.3.2 Extraction Conditions…………………………………………………...31
3.4 Legislation about Heavy Metal Content of Sludge…………………………..34
3.4.1 Legislations of EU, EPA, and Other Countries…………………………34
3.4.2 Legislations of Turkey…………………………………………………..38
CHAPTER FOUR – MATERIALS AND METHODS……………………………...41
4. Materials and Methods…………………………………………………………....41
4.1 Materials……………………………………………………………………...41
4.1.1 The Characteristics of the Sludge Samples……………………………..41
4.2 Methods………………………………………………………………………46
4.2.1 Analytical Methods……………………………………………………..46
4.3 Experimental Procedure……………………………………………………...47
4.3.1 Elutriation Test………………………………………………………….47
4.3.2 Extraction Procedure with Organic Acids………………………………47
CHAPTER FIVE – RESULTS AND DISCUSSION………………………………...49
5. Results and Discussion……………………………………………………………49
5.1 Results of Experimental Studies with Sludge A……………………………...49
5.1.1 Zinc Extraction Studies…………………………………………………49
5.1.2 Copper Extraction Studies………………………………………………51
5.1.3 Nickel Extraction Studies……………………………………………….53
5.1.4 Iron Extraction Studies………………………………………………….55
5.2 Results of Experimental Studies with Sludge B………………………………57
5.2.1 Zinc Extraction Studies…………………………………………………57
5.2.2 Copper Extraction Studies……………………………………………....59
5.2.3 Nickel Extraction Studies……………………………………………….61
5.2.4 Chromium Extraction Studies…………………………………………..63
5.2.5 Iron Extraction Studies………………………………………………….65
5.3 Results of Experimental Studies with Sludge C………………………………67
viii
5.3.1 Zinc Extraction Studies…………………………………………………68
5.3.2 Nickel Extraction Studies……………………………………………….69
5.3.3 Chromium Extraction Studies…………………………………………..71
5.3.4 Iron Extraction Studies………………………………………………….73
5.3.5 Copper Extraction Studies………………………………………………75
5.4 Results of Experimental Studies with Sludge C……………………………...77
5.4.1 Zinc Extraction Studies…………………………………………………77
5.4.2 Nickel Extraction Studies……………………………………………….80
5.4.3 Copper Extraction Studies………………………………………………83
5.4.4 Lead Extraction Studies…………………………………………………85
5.4.5 Iron Extraction Studies………………………………………………….88
5.4.6 Cadmium Extraction Studies……………………………………………90
5.5 Cost Analysis…………………………………………………………………92
CHAPTER SIX – CONCLUSIONS AND RECOMMENDATIONS………………94
6. Conclusions and Recommendations………………………………………………94
6.1 Conclusions…………………………………………………………………..94
6.2 Recommendations……………………………………………………………96
REFERENCES………………………………………………………………………...98
APPENDICES………………………………………………………………………...103
1
CHAPTER ONE
INTRODUCTION
Sludge is produced during the water and wastewater treatment operations.
Industrial sludge is generated at an industrial facility during the treatment of
industrial wastewater. Industrial sludges have often higher concentration of heavy
metals than domestic sludge. The ultimate disposal of heavy metal containing
sludges has been a headache for years. Conversion of sewage sludge into organic
fertilizer for agricultural use is an option for sludge disposal. However, the existence
of concentrated heavy metals in dewatered sewage sludge, especially from industrial
wastewater treatment plant, is a big concern for land application of sludge-made
fertilizer. Heavy metals remaining in the fertilizer may migrate into the subsurface
and eventually cause contamination of soils and groundwater. Due to high heavy
metal contents in sludge, especially in the industrial sludge, the removal of heavy
metal from sludge should perform before composting or land application.
Heavy metal extraction from sludge can be carried out either with solid-to-liquid
extraction or physical separation method. Solid-to-liquid extraction methods are
widely used method. This process is based on the extraction of metals from the solid-
waste to an aqueous-liquid phase followed by separation of the solid and liquid
phase. To promote solubilisation, an extracting agent is added directly (chemical
extraction) or is produced by microorganisms (microbiological leaching).
Several inorganic acids (HNO3, HCl, H2SO4) and strong complexing agents
(NTA, EDTA) have been commonly used for extraction of heavy metals from the
sludge up to now. However, Veeken & Hamelers, 1999 designate that organic
complexing acids (OCAs) such as citric and oxalic acid can be more promising.
Organic acids are more cost effective reagents and also harmless to the environment.
The variable extraction conditions, such as extracting time, reagent concentration,
solids concentration and type of mixing, the ambient temperature, pH are important
2
parameters in the extraction process. The heavy metal transform from solid to liquid
requires good contact between solids and liquid. Therefore, sufficient extracting time
is very important.
In this thesis, solid-to-liquid extraction method was used and the effect of
inorganic acid and organic acid addition was compared. For this purpose, inorganic
acid (HF+HClO4) and organic acids (citric acid, oxalic acid, and acetic acid) were
directly added as an extraction reagent.
The heavy metal extraction studies were carried out using four different industrial
sludges, which were taken from a dyestuff industry, two metal industries, and an
organized industrial district. The extraction efficiencies were determined depending
on the concentration of extracting reagent and extraction time. The most effective
extraction reagent was determined for each heavy metal of each sludge sample. In
the case of one of the organic acid was the most effective reagent, the most effective
extraction time was also determined.
3
CHAPTER TWO
GENERATION AND NATURE OF SLUDGE
2.1 Introduction
Sludge originates from the process of treatment of water/wastewater. “The treatment of
wastewaters invariably produces a residual which must be disposed of into the environment.
Most often this residual is a semisolid, odiferous, unmanageable and dangerous material
commonly termed sludge” (Vesilind, 1979, chap. 1). “Wastewater sludge is a suspension of
both organic and inorganic solids, usually between 1 and 5%, mixed in a liquid that has an
infinity variety of dissolved solids” (Vesilind & Spinosa, 2001, chap. 1).
2.1.1 Sludge Sources
Sewage sludge is generated from urban wastewater treatment plants, septic tank sludge is
generated from septic tanks which contain human excreta and domestic wastewater from
single or multiple human dwellings, and industrial sludge is generated from the treatment of
industrial wastewater of the sectors.
In the water/wastewater treatment, a variety of processes have been used but overall results
of them have the same effective. In essence, the aim of these processes is to separate the waste
into two streams - a clarified water containing around 20-30 mg/L of suspended solids and a
sludge stream of 1-3% solids dry weight. Both streams must be discharged to the
environment. Although the sludge stream has much smaller volume than the other, the
damage, it gives to the environment, has a much greater potential (Priestley, bt).
The properties of sludge originating from the processes of water/wastewater treatment
plant are given respectively as follows.
4
1. Raw sludge is untreated non-stabilized sludge, which can be taken from
wastewater treatment plants. It tends to acidify digestion and produces odour
(http://www.lenntech.com).
2. “Primary sludge is produced in the primary clarifier or settling tank and has
some particularly obnoxious characteristics. It is highly odiferous, it contains
identifiable solid matter that makes it aesthetically unpleasing, and it is
dangerous” (Vesilind & Spinosa, 2001, chap. 1). The composition of this
sludge depends on the characteristics of the catchments area. Primary sludge
consists to a high portion of organic matters, as faeces, vegetables, fruits,
textiles, paper etc. The consistence is a thick fluid with a water percentage
between 93 % and 97 %.
3. The removal of dissolved organic matter and nutrients from the wastewater
takes place in the biological treatment step. It is done by the interaction of
different types of bacteria and microorganisms, which require oxygen to live,
grow and multiply in order to consume the organic matter. The resulting
sludge from this process is called activated sludge. The activated sludge
exists normally in the form of flakes, which besides living and dead biomass
contain adsorbed, stored, as well as organic and mineral part.
4. Primary sludge is often digested to make less objectionable and is then
known as primary digested sludge. Digested sludge accrues during the
anaerobic digestion process. It has a black colour and smells earthy. As a
function of the stabilization degree of anaerobic sludge exhibits an organic
portion of the solid from 45 to 60 % (http://www.lenntech.com).
An alternative to anaerobic digestion is aerobic digestion, which is simply
an extension of the aeration system. Waste activated sludge is aerated in a
separate tank for several days and thus is stabilized in terms of its oxygen
demand and fraction of volatile solids. The resulting sludge is referred to as
aerobically digested sludge.
5
5. Trickling filters are widely used as a biological treatment method for BOD.
The solids that slough off the filter rocks are captured in the final clarifier.
This sludge is called filter humus. Both filter humus and waste activated
sludge are often mixed with raw primary sludge and digested. The resulting
material, called mixed digested sludge, usually is dewatered before its final
disposal.
6. An additional source of sludge in sanitary engineering is the waste from
water treatment. Aluminum sulfate (alum), the most widely used chemical for
coagulation and flocculation in water treatment, produces a sludge known
waste alum sludge (Vesilind, 1979, chap. 1).
Some of the physical characteristics of sludge and corresponding data on the
sludge concentrations to be expected from various processes are given in Table 2.1
(Metcalf & Eddy, 1991, chap. 12).
Table 2.1 Characteristics of sludge and expected sludge concentrations from various treatment
operations and processes. Sludge solids concentration,
% dry solids
Operation or
process
application Range Typical
Characteristics
Primary Sludge 4,0-10,0 5,0
gray and slimy, extremely
offensive odor, digested
under suitable conditions.
Waste Activated
Sludge 0,8-2,5 1,3
has a brownish, flocculant
appearance, is dark under
septic condition, in good
condition inoffensive odor.
6
Sludge solids concentration,
% dry solids
Operation or
process
application Range Typical
Characteristics
Trickling-Filter
Humus Sludge 1,0-3,0 1,5
brownish, flocculant,
inoffensive when fresh,
slowly decomposition,
contains many worms.
Anaerobically
Primary Digested 5,0-10,0 8,0
Anaerobically
*Mixed Digested 2,5-7,0 3,5
Anaerobically digested
sludge is dark brown to
black, contains large
quantity of gas, as sludge
dries, the gasses escape,
musty but not offensive
after digested.
Aerobically
Waste Activated
Sludge
0,8-2,5 1,3
Aerobically
*Mixed Digested 1,5-4,0 2,5
Aerobically digested
sludge is dark brown,
flocculant, not offensive
after digested, dewaters
easily on drying beds
after well – digested.
**Waste Alum 0,5-1,5 gray-yellow, odorless,
very difficult to dewater
* “Mixed” means waste activated sludge + primary sludge
** Source: Vesilind, 1979, pp 5
2.1.2 Sludge Handling and Disposal Methods
Especially, in modern society, amount of sludge that is handled in the wastewater
treatment processes are amazing. Sludge handling is performed for two main
purposes:
7
• Stabilization of the sludge by use of different methods such as biological
(anaerobic and aerobic digestion and composting), chemical (mainly using
lime) and thermal (heat drying, incineration and melting) techniques.
• Volume reduction by use of thickening (gravity thickening, flotation and
centrifugation), de-watering (use of centrifugation, filters and presses),
drying (natural and heat drying) and incineration and melting methods.
(http://www.balticuniv.uu.se)
These methods are described briefly below:
1. Stabilization Methods: Stabilization is used to obtain a sludge that does not
change with time, i.e. a stable sludge that does not cause odour problems.
Biological methods are quite common as the others because of less energy
consuming (http://www.balticuniv.uu.se).
Anaerobic digestion is an appropriate technique for the treatment of sludge
before final disposal and it is employed worldwide as the oldest and most
important process for sludge stabilization. It is a biological process that
produces a gas principally composed of methane (CH4) and carbon dioxide
(CO2) otherwise known as biogas. These gases are produced from organic
wastes such as livestock manure, food processing waste, etc. During the
process, energy rich biogas containing about 2/3 methane gas and 1/3 carbon
dioxide, is produced. The biogas may be used for the aim of energy
production, heating, and electricity production.
Aerobic digestion of sludge is quite common method and aerobic
digestion process aerates the sludge containing biodegradable organic
material for 15 to 20 days. Aerobic digestion requires supplying oxygen to
the sludge. Aerobic digestion has therefore mainly come to be used at small
treatment plants.
8
The other stabilization methods are lime stabilization; heat treatment. The
lime stabilization is performed by addition of lime to untreated sludge in
suitable quantity. As for heat treatment, untreated sludge is heated in a
pressure vessel to temperatures up to 2600C at pressures up to 2760 kN/m2
(Metcalf & Eddy, 1991, chap. 12).
2. Volume Reduction Methods: A significant decrease in moisture content will
greatly reduce the volume of sludge. Thickening is the widely used volume
reduction method. A volume reduction of approximately 30 – 80 % can be
reached with sludge thickening before a further treatment. Metcalf & Eddy
(1991) defines it that is a procedure used to increase the solids content of
sludge by removing a portion of the liquid fraction (chap. 12). Typical sludge
thickening methods are gravity, flotation and centrifugal thickening.
Wastewater sludge thickener performance varies widely, but some typical values are
given in Table 2.2 (Scales, Lester, Dixon, 2001, chap. 17).
Table 2.2. Typical performance of gravitational thickeners
Sludge Type Feed Solids (%) Underflow Solids
(%)
Solids Loading
(kg/m2/d)
Primary
Waste Activated
Anaerobically
digested
2-7
1-3
8
5-10
2-5
12
20-30
7-10
24
According to Pandit & Das (1998), gravity thickening is used for types of sludge
as softening and coagulation sludge. The changes in solids concentration for these
sludges are illustrated in Table 2.3.
9
Table 2.3 Solids concentration before and after thickening for two different sludges
Sludge type Original solids concentration
Solids after gravity thickening
Thickener loadings, lb/day-ft2 (kg/day-m2)
Lime softening 1% 30% 12.5 (61)
Alum coagulation 1% 2% 4 (20)
In the study of Pandit & Das (1998), water treatment sludge is categorized as
softening and coagulation sludge. According to them, coagulation sludges have a
gelatinous appearance are produced from clarifier operations and from the
backwashing of filters. As for softening sludges, these sludges contain mainly
calcium carbonate and magnesium hydroxide precipitates with some organic and
inorganic substances. These sludges dewater easily and processing for ultimate
disposal is common and feasible.
2.1.3 Ultimate Disposal and Fertilizer Value of Sludge
The ultimate disposal of sludge entails two techniques:
1. Landfilling
2. Land application
“Landfills may be on public land such as a municipality owned landfill, or on
private land. Landfill operators commonly require 15 to 30 % sludge (solids). The
minimum concentration required is often determined by local sanitary landfill
regulations” (Pandit & Das, 1998). Landfilling sludge has become expensive because
of the high costs associated with burial in properly constructed landfills. Landfilling
also concentrates organic wastes and may result in point-source contamination for
future generations to deal with (http://lancaster.unl.edu).
Land application of sludge has been used successfully for decades. “Sludges may
be applied to (1) agricultural land, (2) forest land, (3) disturbed land, and (4)
dedicated land disposal sites” (Metcalf & Eddy, 1991, chap.12). The sludge from
10
wastewater treatment is increasingly used as a fertilizer, as it has some advantages,
including the fact that it is often supplied free or cheaply and it contains nutrients
and organic matter. Land disposal is generally considered more environmentally
sound than all other disposal options (Antoniadis, 1998).
Conversion of sewage sludge into organic fertilizer for agricultural use is an
option for sludge disposal. However, the existence of concentrated heavy metals in
dewatered sewage sludge, especially from industrial wastewater treatment plant, is a
big concern for land application of sludge-made fertilizer. Heavy metals remaining in
the fertilizer may migrate into the subsurface and eventually cause contamination of
soils and groundwater. The use of sludge shall be carried out in such a way as to
minimize the risk of negative effects to
(http://europa.eu.int/comm/environment/waste/sludge):
– human, animal and plant health,
– the quality of groundwater and/or surface water,
– the long-term quality of the soil, and
– the bio-diversity of the micro-organisms living in the soil.
The technology for applying sludge is advanced and includes surface spreading
and injection of the material into the soil, a practice which helps reduce the odour
problems and helps the sludge to be more properly incorporated into the soil. The
optimum dose of application is difficult to determine, because there are restrictions
depending on soil parameters, such as pH, clay content and the contaminant and
nitrogen contents in the sludge (Antoniadis, 1998).
Costs can be an important concern in waste disposal and often play an important
part in determining the disposal method used. Also, agricultural use of sludge is often
regarded as the best alternative if the pollutants in the sludge are below guidance and
limiting values. However, the potential problems in land application of sludge
sometimes can occur. The source of these problems can be organic matter,
11
emulsified oil and grease, bacteria and virus, nutrients such as nitrate and phosphate,
and, a legacy of industrial age, heavy metals and organochlorines.
Due to the physical-chemical processes involved in the treatment, the sludge tends
to concentrate heavy metals and poorly biodegradable trace organic compounds as
well as potentially pathogenic organisms (viruses, bacteria, etc.) present in waste
waters. Sludge is, however, rich in nutrients such as nitrogen and phosphorous and
contains valuable organic matter that is useful when soils are depleted or subject to
erosion. The organic matter and nutrients are the two main elements that make the
spreading of this kind of waste on land as a fertilizer or an organic soil improver
suitable (http://europa.eu.int/comm/environment/waste/sludge/index.htm).
A major limiting factor on the application of sludge to agricultural land is the
presence of heavy metals. Even in sludges from non-industrial regions problems can
arise from zinc (phytotoxicity), copper, lead and even cadmium. Cadmium in
particular has been found to accumulate in the food chain and strict limits have been
placed on the level acceptable in sludge (Priestley, bt). Cadmium has had a wide
range of uses in industry, including electroplating, paints and pigments, silver -
cadmium batteries and plastic stabilizers. Nickel is widely used in industry, as it is a
metal which does not corrode as much as Fe. It is, therefore, used in the production
of alloys, on which it confers them stain and corrosion protection. Lead is used as an
absorber of high energy X and γ rays and in roofing, while PbO is used in crystal
glass because it dispenses light spectrally. Industrial uses of Zn include corrosion
protecting coating and manufacture of brass and other alloys. Zinc has a very
similar environmental chemical behavior to Cd, as both elements normally occur
together (Antoniadis, 1998).
2.2 Industrial Sludge
Sludge can be categorized into two main groups: 1) domestic sludge, 2) industrial
sludge. “Industrial sludge is defined as semi-liquid residue or slurry remaining from
treatment of industrial water and wastewater” (http://www.epa.gov).
12
In addition to chemical sludges formed in water and wastewater treatment, many
industries produce waste sludges that must be disposed of. Industrial sludges are
often of little value as soil conditioners and, in fact, are often highly toxic. The
ultimate disposal of such sludges has been a headache for years... The origins of this
sludge vary with the industries producing them. For example, metal-finishing plants
often produce sludges high in zinc, chromium and other heavy metals (Vesilind,
1979, chap. 9).
These components usually occur in small amounts not harmful to plants. Some
heavy metals, including zinc and copper, are micronutrients that are necessary for
plant growth. Excessive amounts of some heavy metals (zinc, copper, nickel) can be
damaging to plants, resulting in reduced yield or even plant death (Muse, 1991)
The most common industrial sources of some heavy metals are shown in the
Table 2.4 (Antoniadis, 1998).
Table 2.4 Most common industrial uses of Cd, Ni, Pb and Zn.
Industry Type Cd Ni Pb Zn
Electroplating x x
Paint pigments x x x
Plastic stabilisers x
Silver-Cd batteries x x x
Coinage x
Water pipes x
Car fuel x
Galvanisation x
Metal antirust coating x x
Roofing x
Absorber of high energy
radiation x
Mining x x x x
Cable coating x
13
Due to high heavy metal contents in sludge, especially in the industrial sludge, the
extraction of heavy metal from sludge should perform before composting or land
application. Chaney and Ryan (1993) have sequenced the negative effects of heavy
metal contents in soil systems as follows:
• Leaching of heavy metal to groundwater systems,
• Heavy metal uptake by plants and animals which introduces more heavy
metals into various vital life-cycles,
• Inhibition of plant growth and of the activity of soil microorganisms.
After removal of heavy metal:
• Sludge can be disposed to landfills with lower risk of heavy metals leaching to
surface and groundwater or uptake by plants,
• Sludge can be used as soil improver,
• Sludge can be applied with lower risk as energy source in co-incineration. In
addition, the off-gas treatment system would be less complex than when the
sludge is metal polluted,
• Dewatered sludge or sludge fly ashes can be applied with lower risk as raw
material for Portland cement and bricks production (Veeken, 2004).
14
CHAPTER THREE
HEAVY METAL EXTRACTION
3.1 Chemistry of Heavy Metals
The heavy metals are metallic chemical element and they have a relatively high
density and are toxic or poisonous at low concentrations. Examples of heavy metals
include mercury (Hg), cadmium (Cd), arsenic (As), chromium (Cr), thallium (Tl),
and lead (Pb).
Heavy metals are natural components of the Earth's crust. Heavy metals are
present in large quantity and enter the water cycle through a variety of geochemical
processes. They cannot be degraded or destroyed. To a small extent they enter our
bodies via food, drinking water and air. As trace elements, some heavy metals (e.g.
copper, selenium, zinc) are essential to maintain the metabolism of the human body.
However, at higher concentrations they can lead to poisoning. Heavy metal
poisoning could result, for instance, from drinking-water contamination (e.g. lead
pipes), high ambient air concentrations near emission sources, or intake via the food
chain.
Heavy metals are dangerous because they tend to bioaccumulate.
Bioaccumulation means an increase in the concentration of a chemical in a
biological organism over time, compared to the chemical's concentration in the
environment. Compounds accumulate in living things any time they are taken up and
stored faster than they are broken down (metabolized) or excreted.
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 (www.lenntech.com). Many metals are also introduced to
water by man-induced activities such as manufacturing, construction, agriculture,
and transportation. Although some metals are not toxic at low concentrations, soluble
metal compounds may be harmful to health and subsequent water use at high
15
concentrations. Water quality conditions such as pH, temperature, hardness, CO2
content and turbidity affect the toxicity levels of heavy metals.
The regulatory agencies have limited the heavy metals discharged to surface
streams from industrial and municipal sources, because of the negative effects of
heavy metals to water supplies. Many industrial establishments discharge wastewater
through the public collection system to the wastewater treatment plant. These
discharges may contain significant quantities of heavy metal that can effect the
collection and treatment system. If any industrial facility discharges wastewater to
the wastewater treatment plant, they should provide pretreatment requirements. Due
to increased environmental legislation, heavy metals need to be removed from
wastewater down to an extremely low residual concentration. The toxic heavy metals
tend to accumulate in the biological systems and thus tend to concentrate. Namely,
what was a low concentration in the influent may be converted to a concentration as
much as twenty to thirty times greater in the solids produced as sludge (Ronald &
Robert, 1981).
In the presence of ambient ligands such as HCO3-, CO3
2-, Cl-, SO42-, an aqueous
divalent contaminant metal (MaqII) can speciate in various free and complex forms:
Maq = M2+ + M (OH)x(2-x) + Mx (OH)y
(2x-y) + M (HnCO3)z2(1-x+n) + MClx
(2-x)
+ M (SO4)x(2-x)
The solubilities of metals are typically too small to effect satisfactory results by
washing with water alone. The solubilites of contaminant metals are controlled by
predominant mineral phases depending upon the pH and/or ambient ligands
available. Commonly observed metal mineral phases include those of oxide,
hydroxide, carbonate, and hydroxy-carbonate, such as MO(s), M (OH)2(s), MCO3(s),
and Mx (OH)y (CO3)z.
16
When the amounts of heavy metals of interest e.g. Pb, Cd, Cu, Zn, Ni exceed the
solubilities of their corresponding hydroxides, carbonates, and/or hydroxy-carbonate
mineral phases at a given pH value, the metals will be precipitated as solids. Hence
these solid minerals will be entrapped in the soil or sediment matrix (Peters, 1999).
At the interaction of solid with metals, effect of pH usually is that, heavy metals
are dissolved under acidic conditions and precipitated under alkaline conditions. The
increasing in the pH of a metal-containing solution should induce precipitation of the
dissolved metal. The increasing pH performs by the addition of alkali such as NaOH
(caustic) or Ca(OH)2 (lime) to provide the hydroxide ions. Thus, the heavy metal
ions in solution react with the hydroxide ions to form solid particles. This specific pH
differs in terms of the other components in the solution such as chelating agents,
surfactants and the other conditions such as temperature (Ronald & Robert, 1981).
The metals adsorbed to the solid phase or present as heavy metal precipitates are
transferred from the solid phase to the liquid phase under acidic condition. Therefore,
the several of acids such as inorganic acids, chelating agents, organic acids are added
to heavy metal – containing sludge. The contact time of acid with sludge and
temperature are significant parameters in the transfer of heavy metals to liquid phase.
3.2 Removal Methods of Heavy Metals from Solid Wastes
Although several studies have been carried out by several researchers, there is no
full scale process for the removal of heavy metals from the organic wastes up to now.
The developed technologies can be classified in to two main groups:
• Solid-to-liquid extraction. This process is based on the extraction of metals
from the solid-waste to an aqueous-liquid phase followed by separation of the
solid and liquid phase. To promote solubilisation, an extracting agent (or
extractant) is added directly (chemical extraction) or is produced by
microorganisms (microbiological leaching).
17
• Physical separation. This process is based on the physical separation of a
specific fraction of the solid waste in which the heavy metals are
concentrated. Physical separation processes are based on differences in
physical properties of different fractions of the solid waste stream (Veeken,
2004).
3.2.1 Solid-to-Liquid Extraction
Extraction scheme for the removal of heavy metals from solid wastes is given in
Figure 3.1. As it is seen from the figure, the extraction process used for the removal
of heavy metals from solids wastes normally performs at three steps.
1. The actual extraction process
2. Separation of the solid and liquid phase
3. Cleaning and recycling of the heavy metal enriched liquid phase (extracting
liquid) (Veeken & Hamelers, 1999).
extracting reactor
solid-liquidseparation
“polluted” waste
extractingreagent “cleaned” waste
heavy metal removal
heavy metal sludge
liquid discharge
recyclingextracting
liquid
Figure 3.1 Extraction scheme for the removal of heavy metals from solid wastes (Veeken, 2004).
18
The applicability of the extraction process for solid wastes or sludge is firstly
determined by the extraction efficiency of the used extracted agent. The extraction
efficiency is defined as the percentage of heavy metals extracted from the solid to the
aqueous phase. Other factors determining the possibilities of the extraction process
are of economical, technological and environmental concern:
1. Costs of the process:
• costs of the extracting reagent,
• number of process units,
• wastewater treatment for liquid discharge.
2. Minimisation of the production of hazardous emissions:
• air emissions,
• water emissions,
• final inert waste.
3. Possible negative effects of the leaching process of the cleaned solid waste on:
• the structure of the waste,
• the bioavailability of essential nutrients in subsequent biological
processes,
• toxicity of heavy metals in subsequent biological processes (Veeken,
2004). Veeken (2004) explains the main mechanisms for the retention of heavy metals in
the solid phase as follows:
1. Adsorption to the organic and inorganic solid phases, e.g. Fe-(hydr)oxides,
clay minerals, organic debris, humic substances
2. Presence as inorganic precipitates, e.g. CdCO3, Cu3(PO4)2, PbS
Two types of reagents for chemical extraction of heavy metals from solid wastes
or sludge are used. These reagents are acids and complexants (chelating agents). Acid
extraction of heavy metals is brought about by the exchange of protons for heavy
metals adsorbed to the solid phase and by the solubilisation of heavy metal
19
precipitates. The protons can either be supplied directly by addition of a strong acid
(e.g. HCl, HNO3, H2SO4, citric acid) or be produced by microorganisms. Extraction
through the production of acids by bacteria or fungi is referred to as microbiological
leaching (Veeken, 2004). For instance, strong organic acids, such as citric acid and
oxalic acid, can be produced by fungi (Burgstaller & Schinner, 1993). H2SO4 can be
produced by the oxidation of reduced sulphur compounds by Thiobacilli strains
(Wong & Henry, 1988). Weak organic acids such as acetic acid and lactic acid can
be produced by a variety of anaerobic consortia (Schlegel, 1993).
According to Veeken (2004), at heavy metal extraction by complexants, because
of the high affinity of the anion for heavy metals, heavy metals adsorbed to the solid
phase or present as heavy metal precipitates are dissolved. The most common
chelating agents, used for the extraction of heavy metals from solid wastes or sludge,
are ethylenediaminoacetic acid (EDTA) and nitrotriacetic acid (NTA). The other
processes, which are more or less based on these two types of reagents, are extraction
with lye, ion exchange and electro-reclamation.
• Extraction with lye (e.g. NaOH): At high pH values humic substances are
solubilised, thus enhancing the solubilisation of heavy metals.
• Ion exchange: The solid ion-exchanger is suspended in the liquid phase and
the metal ions are transported from the contaminated solid waste to the
complexing ion-exchanger.... This process is very complex and rate-limited by
mass transport of heavy metal ions from the bulk solution to the surface of the
ion-exchange particles and by transport of the metal ions from the solid phase
to the liquid phase.
• Electro-reclamation: Mostly applied for in-situ removal of heavy metals from
soils by electrically charging the system through the application of several
electrode arrays; generally the process is promoted by acidification of the soil
(Veeken, 2004).
According to Peters (1999), each conjugate acid / base of the chelating agent may
form a strong complex with the metal, resulting in the formation of various
20
complexes. He designated in his study that total metal solubility with chelators is
much higher than the metal solubility without chelators and for target heavy metals
extraction application, the chelating agents should satisfy the following criteria:
• The chelating agents (with and without the chelated metal) will be compatible
with the foam and will display no adverse effects on the stability of the foam.
• The ligands possess high metal complexing abilities toward heavy and
transition metals as opposed to hard sphere cations such as Ca or Mg. The
relative magnitudes of the equilibrium complexation constants toward heavy
metals and toward alkali metals are an indicator.
• The ligands containing sulfur and nitrogen as donor atoms are generally
preferred for higher selectivity toward metals of interest, which are transition
metals (e.g. Cu2+, Ni2+) and B-type (soft sphere) cations (e.g. Zn2+, Cd2+,
Pb2+, Hg2+). Ligands containing sulfur or nitrogen as donor atoms generally
form more stable complexes with soft sphere metals, whereas ligands
containing oxygen as the donor atom prefer hard sphere cations.
• Multidentate ligands are preferable because they contain multiple
coordinating sites capable of forming more stable complexes with metals
(Peters, 1999).
3.2.2 Physical Separation Processes
If heavy metals are concentrated in specific solid fractions of a solid waste, the
selective removal of these particles from the solid waste generally results in a small
fraction that is highly contaminated and a large fraction that is relatively clean. The
separation of a specific fraction is achieved by means of physical separation
processes. The term 'physical' is added to distinguish this process from molecular
separation processes, such as distillation and dialysis. The processes are widely used
in soil remediation, the mining industry and mineral processing. Until now,
21
adaptations of mining technologies in the field of environmental technology have
been applied only in the cleaning of polluted soils and sediments, where "non-
polluted" sand is separated from polluted smaller size fractions. The separation of a
specific fraction of the solid waste by a solid-solid separation process is established
by differences in particles properties (Veeken, 2004).
The wet solid-solid separation processes widely used in environmental
applications, together with the principal properties on which the separation is based
are shown in Table 3.1. For instance, De Waaij & Van Veen (1990) examined the
heavy metal seperation by hydrocyclones, which is one of the process, at several
types of sediment.
Table 3.1 Waste properties that determine separation in various wet solid-solid separation processes
(Veeken, 2004).
Process Size Density Hydro- phobicity
Shape Magnetic properties
Screening (sieving)
+ (+)1
Elutriation + + (+)
Hydrocyclones + + (+) Air flotation + Magnetic separation
+
1brackets indicate secondary importance
The polluted waste can be qualified by a clean solid stream and a contaminated
solid stream at the physical wet-separation processes used as an environmental
technology. A schematic projection interested in a physical wet-separation process
where the contaminated waste (influent flow) is separated into a “clean fraction” and
a “contaminated fraction” (Figure 3.2). The flows are characterised as follows:
F : the flow rate of the liquid (in m3.s-1),
S : the total solids concentration (in kg.m-3),
C : the concentration of contaminant in the solids (in mg.kg-1 dry matter).
22
The subscripts 'in' and 'con' refer to the incoming flow and contaminated flow,
respectively (Veeken, 2004).
input
FinSinCin
contaminated fraction
FconSconCcon
clean fraction
Figure 3.2. Schematic presentation of physical separation process for environmental applications (Veeken, 2004).
The separation efficiency (ES) with respect to the total contaminated flow is
defined as the total solids mass flow of the contaminated fraction as a fraction of the
total solids feed mass flow rate:
Scon con
in inE =
F SF S
The efficiency of the solid-solid separation process is determined not only by the
total separation efficiency but also by the distribution of the contaminant over the
clean and contaminated flows. The separation efficiency with respect to the
contaminants (EC) is defined as:
C
con con con
in in inS
con
inE =
F S CF S C
= ECC
The removal efficiency of a solid-solid wet-separation process is high when ES is
low and EC is high.
23
The solid waste has to be characterised with respect to particle size distribution
and level of contamination before a separation technology is applied on a pilot-plant
or practical scale.... After the classification, the heavy metal content of the separated
fractions is determined. In this way, it becomes clear to which constituents of the
solid waste the heavy metals are bound. On the basis of these results a separation
technology has to be selected to separate the most contaminated fractions. Most
often a single separation process is insufficient for the separation of a contaminated
solid waste into a clean and a contaminated fraction. Instead a cascade of
separation units is necessary.
There is still a wide gap between the theory and practice of solid-solid separation
processes because the primary properties of a system cannot be easily translated into
equipment. Selection and sizing of the equipment can only be done on the basis of
small-scale tests either in a laboratory or on a pilot-plant scale (Veeken, 2004).
3.3. Extraction from Sludge
The existence of concentrated heavy metals in dewatered sewage sludge,
especially from industrial wastewater treatment plant, is a big problem. Typical metal
content in wastewater sludge and potential heavy metals in sludge and ways to
control them are summarized in Table 3.2 and Table 3.3, respectively.
Table 3.2 Typical metal content in wastewater sludge (Medcalf & Eddy, 1991).
Dry Sludge, mg/kg Metal
Range Median
Arsenic 1,1-230 10
Cadmium 1-3410 10
Chromium 10-99000 500
Cobalt 11,3-2490 30
Copper 84-17000 800
Iron 1000-154000 17000
Lead 13-26000 500
24
Dry Sludge, mg/kg Metal
Range Median
Manganese 32-9870 260
Mercury 0,6-56 6
Molybdenum 0,1-214 4
Nickel 2-5300 80
Selenium 1,7-17,2 5
Tin 2,6-329 14
Zinc 101-49000 1700
Table 3.3 Potential heavy metals in sludge and ways to control them (Muse, 1991).
Heavy Metals Potential Concern Solution
Copper, Zinc, and Nickel Accumulation in topsoil; toxic to plants at high levels
Reduce source of metal in sludge; apply according to soil loading limits; lime soil
Cadmium Accumulation in topsoil; taken up by plant and accumulates in leafy material; accumulates in animal organs; human health
Reduce source of metal in sludge; apply according to soil loading limits; lime soil
Lead Accumulation in topsoil: Potentially harmful if excessive amounts are ingested with soil particles by animals
Reduce source of metal in sludge; apply according to soil loading limits; lime soil
Mercury, Chromium, Selenium, Arsenic, and Antimony
Little concern unless present in extremely high amounts
Extraction of heavy metals from sludge typically consists of three steps. In the
first step of the extraction process the heavy metals are transferred from the solid
phase to the aqueous phase. This requires good contact between solids and liquid
which is brought about by intensive mixing. In the second step the aqueous phase is
separated from the ‘cleaned’ sludge by a solid-liquid separation process, e.g.
decanting centrifuge. In the third step the (heavy) metals are removed from the
25
extracting solution to recover the economical value of the extracting agent and
prevent environmental impact associated with discharge of extracting liquid. The
most appropriate and economically feasible technologies for removal of heavy
metals from solutions are chemical sulphide precipitation and/or selective ion-
exchange (Veeken & Hamelers, 1999).
3.3.1. Extraction Reagents
Various inorganic acids (HNO3, HCl, H2SO4) and strong complexing agents
(NTA, EDTA) are proposed in literature. Inorganic acids and complexing agents
however are not applicable on a practical scale due to (1) the costs of the process
and (2) the negative environmental impacts of the discharged solid and liquid waste
streams (Wong & Henry 1988). Veeken & Hamelers (1999) designate depending on
the following reasons that organic complexing acids (OCAs) such as citric and oxalic
acid can be more promising.
1. Heavy metal extraction is partly due to the acidic character but for the greater
part to the complexing behaviour of OCAs; therefore extraction can be
performed at mildly acidic conditions (pH 3-5),
2. OCAs are readily biodegradable under both aerobic and anaerobic
conditions. This implies that the ‘cleaned’ sludge does not have to be
conditioned, thus leading to a substantial reduction of wastewater. Moreover,
wastewater can be treated (an)aerobically,
3. Heavy metals can be removed from OCAs solution. In this way, the extraction
liquid can be recycled, reducing the costs of the process.
Like inorganic acids and strong complexing agents, organic acids are not
selective and also metals other than heavy metals are simultaneously extracted from
the sludge. The major cations competing with heavy metals for citric acid are Ca,
Mg, Fe and Al (here referred to as ‘competing’ metals). Therefore, citric acid has to
be dosed to sewage sludge in an equimolar amount to the cumulative content of
26
complexing metals. This last point is often overlooked in relation to heavy metal
extraction by complexing agents. Moreover, for recovery of OCAs not only heavy
metals but also competing metals have to be removed from the extracting liquid.
Otherwise, the competing metals are accumulated in the extraction reactor, in this
way lowering the heavy metal extracting capacity of OCAs.
3.3.1.1. Organic Acids
The structure and properties of organic acids (citric, oxalic, and acetic) are
described below in detail:
1. Citric acid (C6H8O7): It is a weak organic acid found in citrus fruits. It is a
good, natural preservative and is also used to add an acidic (sour) taste to
foods and soft drinks. In biochemistry, it is important as an intermediate in
the citric acid cycle and therefore occurs in the metabolism of almost all
living things. It also serves as an environmentally friendly cleaning agent and
acts as an antioxidant (http://en.wikipedia.org/wiki/Citric_acid). Its structure
is shown in Figure 3.3.
Figure 3.3 The chemical formula of citric acid.
The acidity of citric acid results from the three carboxy groups (COOH)
which can lose a proton in solution. If this happens, the resulting ion is the
citrate ion. Citrates make excellent buffers for controlling the pH of acidic
solutions. Citrate ions form salts called citrates with many metal ions. An
important one is calcium citrate or "sour salt… Additionally, citrates can
27
chelate metal ions, which gives them use as preservatives and water
softeners.... Similarly, citric acid is used to regenerate the ion exchange
materials used in water softeners by stripping off the accumulated metal ions
as citrate complexes.
At room temperature, citric acid is a white crystalline powder....
Chemically, citric acid shares the properties of other carboxylic acids. When
heated above 175°C, it decomposes through the loss of carbon dioxide and
water.... Citric acid is recognized as safe for use in food… It is naturally
present in almost all forms of life, and excess citric acid is readily
metabolized and eliminated from the body
(http://en.wikipedia.org/wiki/Citric_acid).
2. Oxalic Acid (ethanedioic acid): It is a bi-carboxylic acid with structure
(HOOC)-(COOH). Because of the joining of two carboxyl groups, this is one
of the strongest organic acids. The anions of oxalic acid as well as its salts
and esters are known as oxalates. Oxalic acid and oxalates are mild toxins
found in many plants. Oxalic acid is a strong acid that irritates the lining of
the gut when consumed, and can prove fatal in large doses. Oxalic acid also
combines with metals such as calcium in the body to form oxalates which
further irritate the gut and kidneys. The most common kind of kidney stone is
made of calcium oxalate.
Because it binds vital nutrients such as calcium, long-term consumption of
foods high in oxalic acid can lead to nutrient deficiencies. Healthy
individuals can safely consume such foods in moderation, but those with
kidney disorders, gout, or rheumatoid arthritis are typically advised to avoid
foods high in oxalic acid or oxalates….In addition to its natural occurrence
in plants, oxalic acid may also be found in household chemical products such
as some bleaches, rustproofing treatments and wood restorers - where the
acid dissolves away a layer of dry surface wood to expose fresh material
underneath (http://en.wikipedia.org/wiki/Oxalic_acid).
28
3. Acetic Acid: It is a carboxylic acid with chemical formula C2H4O2, often
written as CH3COOH to better reflect the structure is shown in Figure 3.4.
Acetic acid is a molecule central to biochemistry, and is produced in some
amount by nearly all forms of life…. Acetic acid is produced naturally as
fruits and some other foods spoil, and it is one of the oldest chemicals known
to humanity.
Figure 3.4 The chemical formula of acetic acid.
Pure acetic acid is a colorless, corrosive, flammable liquid that freezes at
16.6 °C. Because pure acetic acid freezes only slightly below room
temperature and has an ice-like appearance when it does so, it is often called
glacial acetic acid. In aqueous solution, acetic acid can lose the proton of its
carboxyl group, turning into the acetate ion CH3COO-. The pKa of acetic
acid is about 4.8 at 25 °C, meaning that about half of the acetic acid
molecules are in the acetate form at a pH of 4.8. As a vapor, acetic acid does
not consist of individual acetic acid molecules. Instead, it consists mostly of
pairs of acetic acid molecules hydrogen bonded to one another. As a result,
acetic acid vapors behave in a way that grossly violates the ideal gas law.
Most acetic acid made for industrial use is made by one of three chemical
processes: methanol carbonylation, butane oxidation, or acetaldehyde
oxidation. In the form of vinegar, acetic acid is used directly as a condiment,
and also in the pickling of vegetables and other foodstuffs…. The glacial
acetic acid produced by the chemical industry is used in the manufacture of
photographic films and stop bath and sometimes in the production of the
plastic polyethylene terephthalate (PET)…. Dilute solutions (4% - 6%) of
acetic acid are extremely useful in treating the sting of the box jellyfish; the
29
acid disables the stinging cells of the jellyfish, and can prevent serious injury
or death if immediately applied. Some of the esters of acetic acid are
commonly used solvents and artificial flavorings.
Concentrated acetic acid is corrosive and has to be handled with care,
since it can cause skin burns, permanent eye damage, and irritation to the
mouth, nose, throat, and lungs. It can penetrate the skin, and it may not
produce burns or blisters for several hours after exposure. Dilute acetic acid
(in the form of vinegar) is harmless and has been consumed for millennia.
However, ingestion of stronger solutions or the glacial acid is dangerous,
resulting in severe damage to the digestive system, and a potentially lethal
change in the acidity of the blood. Acetic acid poses no known cancer risk
(http://en.wikipedia.org/wiki/Acetic_acid).
3.3.1.2. Standart Methods
According to Standart Methods, to reduce interference by organic matter and to
convert metal associated with particulates to a form (usually the free metal) that can
be determined by atomic absorption spectrometry or inductively-coupled plasma
spectroscopy, use one of the digestion techniques. These techniques are as follows
(APHA, AWWA, WEF, 1992):
• nitric acid digestion (section 3030 E)
• nitric acid-hydrochloric acid digestion (section 3030 F)
• nitric acid-sulfuric acid digestion (section 3030 G)
• nitric acid-perchloric acid digestion (section 3030 H)
• nitric acid- perchloric acid-hydrochloric acid digestion (section 3030 I)
3.3.1.3. Squential Extraction Method
Heavy metals occur in sludges in various abiotic (physicochemical) forms, such
as, soluble, adsorbed, exchangeable, precipitated, organically complexed, and
30
residual phases. Heavy metals may also exist in biotic forms, such as extracellular
and intracellular species. The variety of heavy metal forms significantly influences
their environmental mobilities and bioavailability, and finally determines the
potential for environmental contamination. If heavy metals exist as loosely bound
fractions, such as, soluble, exchangeable and adsorbed forms, they tend to be easily
moved and dispersed. However, metals associated with organic ligands or in crystal
lattices are not easily seperated or mobilized (Kim et al., 2002).
Therefore, to determine the speciation of heavy metals is very important.
Sequential extraction analysis is one of the digested methods have been suggested.
This sequential extraction scheme consists of several extraction steps. Bound
fractions of heavy metals to sludge in each step are retained by additional of a variety
of chemical extract ants. The researcher, examine determination of heavy metal
contents from sludge, usually modify and utilize from the sequential extraction
procedure described by Tessier et al. (1979), Ure et al. (1993), Quevauviller et al.
(1997) and the others (Fuentes et al., 2004; Kim et al., 2002; Scancar et al., 2000).
For example, Scancar et al. (2000) examined various heavy metal extractions using
sequential extraction method according to procedure given by Quevauviller (1997).
They used four steps: At first step, metals present in ionic form, bound to carbonates
and the exchangeable fraction are extracted. At second step, metals bound to
amorphous iron and manganese oxides and hydroxides are leached. At third step,
metals bound to organic matter and sulphides are extracted. At last step, metals
bound to silicate lattice or crystalline iron and manganese oxides.
3.3.1.4. Summary of Case Studies
The extraction of heavy metals from sewage sludge has been studied extensively.
Ito et al. (1999) examined the removal of heavy metals from anaerobically digested
sewage sludge by using ferric sulfate as extracting regeant. They observed that the
addition of ferric sulfate to the sludge caused the subsequent elution of heavy metals
such as Cd, Cu and Zn from the sludge due to the acidification of the sludge. The
elution percentage of these metals increased with an increase in the amount of iron
31
added and with a decrease in the sludge concentration. This study resulted with the
elution percentage of cadmium, copper and zinc was more than 80%.
A compilation of literature data regarding the extraction efficiencies of Cd, Cu, Pb
and Zn from sewage sludge is demonstrated in
Table 3.4. The table shows a very broad range of extraction efficiencies for heavy
metals given follow. “The broad range in extraction efficiencies is due to differences
in sludge composition, differences in pretreatment of the sludge and differences in
extracting conditions” (Veeken, 2004).
Table 3.4. Extraction efficiency of heavy metals from sewage sludge (in %)(Veeken, 2004).
Extracting reagent Cd Cu Pb Zn Reference
0.5 M acetic acid 40 0 5 25
Bloomfield & Pruden,
1975
HCl, pH 1.5 10-90 0-70 5-100 50-90 Oliver & Carey, 1976
H2SO4 10-70 <2 10-15 35-70 Jenkins, 1981
HCl, pH 1.5 80-100 80-100 40-100 100 Wozniak &
Huang, 1982
HCl, pH 1 90 50 - 90 Ried, 1988 H2SO4, pH 1.5 - 50-75 50-60 80-95 Tyagi et al.,
1988
HCl, pH 1 22-90 2-90 30-100 50-95 Rulkens et al., 1989
H2SO4, pH 1.5 95-99 8-10 35-65 50-99 Lo & Chen,
1990
3.3.2. Extraction Conditions
The variable extraction conditions, such as extracting time, reagent concentration,
solids concentration and type of mixing, the ambient temperature, pH are important
parameters in the extraction process.
32
According to Veeken and Hamelers (1999), as might be expected, the extraction
efficiency increases for lower pH values. Besides, they reached in their study that the
rate of extraction increases for Cu and Zn at higher temperatures and citric acid
concentrations. The lower solubility is caused by the reduction of sulphate to
sulphide and the subsequent precipitation of heavy metal sulphides. Heavy metal
sulphides, especially CuS and PbS, are very difficult to solubilise, even at low pH
values. Also, the lower solubility of Cu is due to the stronger binding of Cu to sludge
biomass (Veeken, 2004).
Veeken and Hamelers (1999) obtained in their study as regards OCAs those
extractions were performed for oxalic acid and citric acid at various concentrations in
pH range 2-6 for Cu, Zn, Ca and Fe. Both acids increased the heavy metal extraction
efficiency at mildly acidic pH. Citric acid had higher extraction efficiencies
compared to oxalic acid because oxalic acid is removed from solution by
precipitation as calcium oxalate and citrate anion is protonated. At low pH, the
extraction can be assisted to the action of the protons. Besides, binding degree of
metal ions to the sludge is important.
33
0
20
40
60
80
100
0 3 6 9 12
time (d)
extra
ctio
n (%
)
12.6 5 1.3
Ca
0
20
40
60
80
100
0 3 6 9 12
Zn0
20
40
60
80
100
0 3 6 9 12
extra
ctio
n (%
)
Cu
0
20
40
60
80
100
0 3 6 9 12
time (d)
12.6 5 1.3
Fe
Figure 3.5 Kinetics of extraction of Cu, Zn, Ca and Fe from sewage sludge at various citric acid
concentrations (Veeken & Hamelers, 1999).
The kinetics of the extraction process were studied for citric acid extraction at
various concentrations at pH 3 (Figure 3.5). The course of extraction showed a
distinct difference between heavy metals (Cu, Zn) and competing metals (Ca, Fe).
The extraction of Cu and Zn as a function of time is typical for the extraction of
heavy metals from sewage sludge: less strongly bound heavy metals (Zn) are
extracted more rapidly from the sludge than strongly bound heavy metals (Cu).
Heavy metals are predominantly incorporated in sludge flocs and the extraction
takes time because the heavy metals have to diffuse from the sludge matrix to the
bulk solution. The metals Ca and Fe are extracted much more rapidly from sewage
sludge because these metals are present as precipitate (e.g. Fe(OH)3, FePO4,
CaCO3) or very weakly adsorbed to sludge flocs (Ca). The dissolution of precipitates
is a relatively fast process compared to the diffusion of metal ions from within the
sludge flocs to the bulk solution. The extraction was also studied at 10, 20 and 30 oC
for the extraction with 0.1 M citric acid at pH 3.5. The increase in rate of extraction
for both Cu and Zn with increasing temperature confirms the hypothesis that the rate
34
of extraction is controlled by diffusion of metal ions from the sludge flocs to the bulk
solution.
Heavy metals and competing metals both have to be removed from the extracting
liquid to prevent accumulation of these metals in the process. Citric acid is a
moderately strong complexing agent and both heavy and competing metals can
possibly be removed from the liquid phase by a combination of chemical sulphide
precipitation and specific ion exchangers.
Extraction of heavy metals from organic wastes by citric acid could be an
attractive option because the extraction can be performed at mildly acidic conditions
(pH 3-5). As citric acid is biologically degradable, the extraction process is
compatible with composting and wastewater treatment. The extraction was studied
for heavy metals Cu and Zn and for competing metals Ca and Fe from polluted
sewage sludge. The rate of extraction increases for increasing temperature and citric
acid concentration. Cu can be extracted for 60-70% and Zn for 90-100% by citric
acid at pH 3-4. However, the process is still critical with respect to the removal of
competing and heavy metals from the recycling liquid. Moreover, the process results
in a highly toxic metal sludge that has to be landfilled. A first economic valuation of
the extraction process showed that the total costs of the treatment process are high
and comparable to the costs of incineration, approx. €400 per ton of dry matter
(Veeken, 2004).
3.4 Legislations about Heavy Metal Content of Sludge
3.4.1 Legislations of EU, EPA, and Other Countries
The purpose of using sludge in agriculture is partly to utilise nutrients such as
phosphorus and nitrogen and partly to utilise organic substances for soil
improvement. However, an important consideration in this application is the heavy
metal content of the sludge. At a pH greater than 6, heavy metals will exchange for
Ca+2, Mg+2, Na+ and K+. This natural ability to Exchange heavy metals by the soil is
35
called the Cation Exchange Capacity (CEC) and is expressed in milliequivalents per
hundred grams of dry soil. The U. S. Department of Agriculture has listed the
maximum amount of heavy metals that can be applied to the land , as shown in Table
3.5 (Eckenfelder, 1989). Maximum loadings of heavy metals have been tentatively
adopted by the EPA.
Table 3.5 Suggested maximum heavy metals can be applied .
Soil Cation Exchange Capacity, milliequivalents/ 100 g
0-5 5-15 >15 Metals
The Amount of Heavy metal (lbre/acre)*
Zn 225 450 900
Cu 110 225 450
Ni 45 90 180
Cd 4,5 9 18
Pb 450 900 1 800 * lbre/acre = 0,112 g/m2 = 1,12 kg/ha
Table 3.6 gives comparative data from a number of countries on the maximum
allowable concentrations of heavy metal in sludge (Priestley, bt).
Table 3.6 Maximum permitted concentrations of heavy metals in sewage sludge used for land
application (mg/kg dry solid).
Heavy
Metals
The
Netherlands France Sweden Japan NSW
Arsenic 10 - - 50 15
Mercury 5 10 8 2 10
Cadmium 5 40 15 5 8-20
Chromium 500 1 000 1 000 - 500
Lead 500 800 300 - 500
Nickel 100 200 500 - 100
Zinc 2 000 3 000 10 000 - 1 800
Copper 600 1 000 3 000 - 1 200
36
Table 3.7 demonstrates sewage sludge metal level standards proposed by
European Council.
Table 3.7 European Council Directive 86/278/EEC sewage sludge metal level standards (Hutton&
Meeus, 2001).
Metals
Limit Values for Concentrations of Heavy Metals in
Soil Soil with pH of 6-7
mg/kg
Limit Values for Heavy-Metal
Concentrations in Sludge for Use in
Agriculture mg/kg
Limit Values for Amounts of Heavy
Metals which may be Added Annually to Agricultural Land (Based on 10-Year
Avg.) kg/ha/yr
Cadmium
1 to 3 20 to 40 0.15
Copper
50 to 140 1 000 to 1750 12
Nickel
30 to 75 300 to 400 3
Lead
50 to 300 750 to 1 200 15
Zinc
150 to 300 2 500 to 4 000 30
Mercury
1 to 1.5 16 to 25 0.1
Chromium 100 to 150 1 000 to 1 500 4
Table 3.8 is given in a study performed by EPA (1994). This document explains
the requirements applicable to land appliers of sewage sludge. 40 CFR 503.13 means
40 Code of Federal Regulations Part 503. Ceiling concentration establishes the
maximum concentration of each pollutant that sewage sludge can contain and still be
land applied. Cumulative Pollutant Loading Rates establish the maximum amount
(mass) of each regulated pollutant that can be applied to a site during the life of the
site. Annual Pollutant Loading Rates establish the maximum amount (mass) of
pollutants in sewage sludge that can be applied to a site during a 365-day period.
37
Table 3.8 Pollutant limits for the land application of sewage sludge (EPA, 1994).
Concentration Limits
Pollutant Ceiling Concentrations
(Table 1 of 40 CFR 503.13) mg/kg,dry weight
Pollutant Concentration (Table 3 of 40 CFR 503.13)
mg/kg,dry weight Arsenic 75 41
Cadmium 85 39
Chromium 3000 1200
Copper 4300 1500 Lead 840 300
Mercury 57 17 Molybdenum* 75 --
Nickel 420 420 Selenium 100 36
Zinc 7500 2,800 Loading Rates
Cumulative Pollutant Loading Rates
(Table 2 of 40 CFR 503.13)
Annual Pollutant Loading Rates
(Table 4 of 40 CFR 503.13) Pollutant
kg/he, dry weight
libre/acre, dry weight
kg/he/365 days,
dry weight
libre/acre/365 days,
dry weight Arsenic 41 37 2,0 1,8
Cadmium 39 35 1,9 1,7
Chromium 3000 2677 150 134
Copper 1500 1339 75 67 Lead 300 268 15 13
Mercury 17 15 0,85 0,76 Molybdenum* -- -- -- --
Nickel 420 375 21 19 Selenium 100 89 5,0 4,5
Zinc 2800 2500 140 125 * The pollutant concentration limit, cumulative pollutant loading rate, and annual pollutant loading rate for molybdenum were deleted from Part 503 effective February 19, 1994. EPA will reconsider establishing these limits at a later date.
Table 3.9 gives the limit values for concentrations of heavy metals in soil
depending on the European Union Directives. When the concentration value of an
element in a specific land area is higher than the concentration limit as set in the
38
table, the competent authority may allow the use of sludge on that land on a case-by-
case basis and after evaluation of the following aspects:
• uptake of heavy metals by plants,
• intake of heavy metals by animals,
• groundwater contamination,
• long term effects on bio-diversity, in particular on soil biota.
Table 3.9 Limit values for concentrations of heavy metals in soil (http://europa.eu.int).
Limit Values (mg/kg DM) (Directive 86/278/EEC)
Elements 6<pH<7 5≤pH<6 6≤pH<7 pH≥7
Cd 1-3 0,5 1 1,5
Cr - 30 60 100
Cu 50-140 20 50 100
Hg 1-1,5 0,1 0,5 1
Ni 30-75 15 50 70
Pb 50-300 70 70 100
Zn 150-300 60 150 200
3.4.2 Legislations of Turkey
The directives about sludge are given in Legislations of Solid Waste Management
(Official Gazette, 1991), Legislations of Hazardous Waste Management (Official
Gazette, 1995), and Legislations of Soil Contamination Management (Official
Gazette, 2001) in Turkey. The directives related with heavy metal given in these
Legislations are summarized in the Table 3.10 - 3.12.
39
Table 3.10 Limit values of heavy metals in soil for Turkey as different years.
Soil Contamination Control Directive (2001) Heavy
Metal PH ≤ 6
mg/kg DS
PH>6 mg/kg DS
Soil Contamination Control Directive
(1991) (pH is not denoted)
Lead 50 ** 300 ** 100
Cadmium 1 ** 3 ** 3
Chrome 100 ** 100 ** 100
Copper * 50 ** 140 ** 100
Nickel * 30 ** 75 ** 50
Zinc * 150 ** 300 ** 300
Mercury 1 ** 1,5 ** 2
* If pH value is higher than 7, the heavy metal levels can be increased up to 50% by Ministry ** The heavy metal levels can be increased if it is proved to be harmless for human health in cropland by the scientific studies.
Table 3.11 Maximum allowable heavy metal content in sewage sludge used in agriculture for Turkey
as different years
Heavy Metal Limit value for 2001 (mg/kg DS)
Limit value for 1991 (mg/kg DS)
Lead 1200 1200
Cadmium 40 20
Chromium 1200 1200
Copper 1750 1200
Nickel 400 200
Zinc 4000 3000
Mercury 25 25
40
Table 3.12 Maximum heavy metal loadings which may be added annually to agricultural land (based
on 10-Year Avg.) in Turkey as different years.
Heavy Metal Limit loading value**
for 2001 (g/ha/yr)
Limit loading value for 1991 (g/ha/yr)
Lead* 1500 2000
Cadmium 15 33
Chromium* 1500 2000
Copper* 1200 2000
Nickel* 300 330
Zinc* 10 42
Mercury 3000 5000
* The limit loading values of heavy metals except for Cd and Hg can be increased up to 5% by Ministry respecting suggestions of related Institutions in the case of three months duration between sludge applications to the land and harvesting (for 2001) ** These values can be exceeded in the case of it is used at animal food growing land and scientific studies are proved that it is not harmful for human and environment.
41
CHAPTER FOUR
MATERIALS AND METHODS
4.1. Materials
4.1.1 The Characteristics of the Sludge Samples
Lab-scale experiments were carried out with four different industrial sludges. The sludges
were taken from a dyestuff industry (Sahan Dyestuff Industry, Torbali), two metal industries
(Norm Cıvata and Cevher Döküm), and an Organized Industrial District (Atatürk Organized
Industrial District). The first metal industry, the dyestuff industry, the Organized Industrial
District (OID), and the second metal industry sludge is named as “Sludge A”, “Sludge B”,
“Sludge C”, and “Sludge D”, respectively, in the thesis. All of the sludges were dewatered
sludge.
Before extraction studies with organic acids were started, general properties of each sludge
sample had been determined. In these characterization experiments, total solids (TS) and total
volatile solids (TVS) of the samples were taken into consideration. In addition, the heavy
metal contents of sludge were determined using HF+HClO4 digestion method depending on
the procedure described in Section 4.3. The results of the characterization studies are given in
Table 4.1 – 4.4.
42
Table 4.1 General properties of “Sludge A” taken from a metal industry.
Parameter Unit Value
Total Solids, TS mg/g 350
Total Volatile Solids, TVS mg/g 82
Dry Matter % 34,96
Organic Matter % 8,23
Total Fe
mg/kg
mol/kg
92 220
1,65
Zn2+
mg/kg
mol/kg
65 000
1,00
Cu2+
mg/kg
mol/kg
4,8
0,000075
Total Cr
mg/kg
mol/kg
99
0,0019
Ni+
mg/kg
mol/kg
1 820
0,031
Na+
mg/kg
mol/kg
7 600
0,33
K+
mg/kg
mol/kg
200
0,0051
Ca2+
mg/kg
mol/kg
536
0,0134
Mg2+
mg/kg
mol/kg
2 100
0,086
Total Metal Content* 0,34
*sum of heavy and competing metals in mol/kg DM
43
Table 4.2 General properties of “Sludge B” taken from a dyestuff industry.
Parameter Unit Value
Total Solids, TS mg/g 683
Total Volatile Solids, TVS mg/g 170
Dry Matter % 68,30
Organic Matter % 17
Total Fe
mg/kg
mol/kg
80 200
1,43
Zn2+ mg/kg
mol/kg
24 120
0,37
Cu2+ mg/kg
mol/kg
311
0,0049
Total Cr mg/kg
mol/kg
694
0,013
Ni+ mg/kg
mol/kg
244
0,0041
Na+ mg/kg
mol/kg
36 400
1,58
K+ mg/kg
mol/kg
600
0,015
Ca2+ mg/kg
mol/kg
75 400
1,885
Mg2+ mg/kg
mol/kg
12 860
0,53
Total Metal Content* 0,65
*sum of heavy and competing metals in mol/kg DM
44
Table 4.3 General properties of “Sludge C” taken from an OID.
Parameter Unit Value
Total Solids, TS mg/g 201
Total Volatile Solids, TVS mg/g 84
Dry Matter % 20,10
Organic Matter % 8,40
Total Fe
mg/kg
mol/kg
83 940
1,498
Zn2+
mg/kg
mol/kg
9 680
0,149
Cu2+
mg/kg
mol/kg
702
0,011
Total Cr
mg/kg
mol/kg
1 093
0,021
Ni+
mg/kg
mol/kg
368
0,0062
Pb2+
mg/kg
mol/kg
7,8
0,00038
Na+
mg/kg
mol/kg
61 200
2,66
K+
mg/kg
mol/kg
2 600
0,066
Ca2+
mg/kg
mol/kg
48 000
1,2
Mg2+
mg/kg
mol/kg
11 200
0,461
Total Metal Content* 0,61
*sum of heavy and competing metals in mol/kg DM
45
Table 4.4 General properties of “Sludge D” taken from a metal industry.
Parameter Unit Value
Total Solids, TS mg/g 402
Total Volatile Solids, TVS mg/g 243
Dry Matter % 40,20
Organic Matter % 24,30
Total Fe
mg/kg
mol/kg
2 232
0,0398
Zn2+
mg/kg
mol/kg
8 532
0,1313
Cu2+
mg/kg
mol/kg
237,6
0,0037
Total Cr
mg/kg
mol/kg
---
---
Ni+
mg/kg
mol/kg
152
0,0026
Na+
mg/kg
mol/kg
78 000
3,3913
K+
mg/kg
mol/kg
2 800
0,0718
Ca2+
mg/kg
mol/kg
120 000
3,0
Mg2+
mg/kg
mol/kg
4 200
0,173
Total Metal Content* 0,85
*sum of heavy and competing metals in mol/kg DM
46
4.2. Methods
4.2.1 Analytical Methods
Industrial sludge collected from the four wastewater treatment plants placed in
Izmir was examined in this study. The collected sludge samples were stored at 4°C
until used. The general characteristics of the sludge were determined before heavy
metal extraction with organic acids.
To determine composition of the sludge samples, total solid content (TS) and total
volatile solids (TVS) were determined according to procedure given in Standard
Methods (APHA, AWWA, WEF; 1992). The total metal concentrations were
measured after digestion of samples with strong acids including HF and HClO4
treatment (APHA, AWWA, WEF; 1992). The concentrations of heavy metals and
Fe, Ca, and Mg in the final solutions were determined by an atomic absorption
spectrometer (AAS) (UNICAM 929). Na+ and K+ were measured using a flame
photometer (JENWAY PFP 7).
Total solid is the sum of the dissolved and suspended solids in the sludge and is
determined by drying a sample at 105oC and weaving the residue. The determination
of the total solids of a sludge sample is required for determining the moisture content
of the sludge, usually expressed as percentage of wet weight, and for expressing
other constituents on a dry weight basis.
The volatile solids content of sludge, generally expressed as a percentage, is used
as a measure of the organic content of sludge. Volatile solids reduction is used as a
measure of the performance of the digester. The volatile solids are determined by the
loose in weight when the sludge is combusted by heating a sample to 550oC
(Lue-Hing, Zenz, & Kuchenrither, 1992).
47
4.3 Experimental Procedure
4.3.1 Elutriation Test
The total heavy metals contents of industrial sludge samples were determined
using HF-HClO4 digestion method. At the beginning of the experiment, a platinum
container was carefully cleaned and heated in a furnace at 800oC for 15-20 minutes
and then weighed. After sludge sample was dried and ground, 0,5 gram of the sample
was put in the platinum container. And then, 1 ml HClO4 and certain amount of HF
acid were added in the sample. In order to obtain pre-degradation, prepared sample
was placed above a heater. When the level in the platinum container decreased, HF
acid was added again.
In the meantime, 100 ml pure water and 5 ml HCl acid were added into 250 ml of
a beaker at a different place. When the level in the platinum container decreased
again, the platinum container was put in the beaker. When the level in the beaker
abated three times, the beaker was taken from the heater. The solution in the beaker
was conducted from a blue filter band and the filtrate was completed to 100 ml by
pure water. The prepared filtrate for heavy metals analysis was kept in the
refrigerator at 4oC until they were analyzed by atomic absorption spectrometer
(UNICAM 929).
4.3.2 Extraction Procedure with Organic Acids
The sludges, which were taken from different industrial sources, were stored at
+4°C until analysed. After then, each sludge sample was dried in an oven at 103-
105oC for 1-2 days, depending on the structure of sludge. In order to get ready the
sludge sample to extraction analyses with organic acid, dried sludge was ground.
Although citric acid and oxalic acid were used as main organic acids at this study,
acetic acid was also applied to the sludge sample originating from a metal industry
(Sludge D) used at the end of this study.
48
The amount of the extracting reagent applied during the organic acid extraction
was determined from the sum of heavy metals of raw sludge samples, which were
determined using HF+HClO4 digestion method. The amount of organic acid was
adjusted as it is larger than the sum of them and at this study, 1 mol, 2 mol, and 5
mol citric, oxalic acid, and acetic acid was examined at room temperature.
5 gram of dried sludge sample was placed in a shaken flask with selected amount
of extracting reagent. pH was measured before stirring. Flasks were kept in stirring
conditions (70 rpm) at room temperature using a shaker (Roto-Torque, heavy duty
rotator). The samples, which were taken after 1 h, 3 h, 24 h, and 72 h of extraction
time, were centrifuged at 5000 rpm during 30 minutes and filtered over firstly a black
filter band and secondly a blue filter band. The filtrate was completed to 100 ml with
pure water and then, stored at 4oC before analysis. Na+ and K+ were analyzed by a
flame photometer and the other heavy metals were determined by atomic absorption
spectrometer as mg/l. These values were transformed to mg/kg by considering
dilutions.
49
CHAPTER FIVE
RESULTS AND DISCUSSION
The results of experimental studies carried out with organic acids for four
different sludges are discussed below. In addition, all results are also given as table
form at Appendix.
5.1 Results of Experimental Studies with Sludge A
Sludge A was taken form a Metal Industry. The characteristics of the sludge
sample are given in Chapter 4 (see Table 4.1). Comparisons of extraction results
carried out using different organic acids-citric acid, oxalic acid- and the conventional
HF + HClO4 digestion method for Sludge A are debugged in the following
subsections. The extraction of heavy metals accomplished by different organic acids
was performed at different extraction times for 1 h (0,04 d), 3 h (0,125 d), 24 h (1 d),
and 72 h (3 d).
5.1.1 Zinc Extraction Studies
Citric Acid Results
Citric acid (C6H8O7) with three different concentrations (1, 2, and 5 mol) and the
conventional HF + HClO4 digestion were applied to Sludge A for the extraction of
heavy metals. The results for this application and the conventional method are
depicted in Figure 5.1.
50
0
10000
20000
30000
4000050000
60000
70000
80000
90000
1 mol CA 2 mol CA 5 mol CA HF+HClO4
Extraction Reagent
Ext
ract
ed Z
n (m
g/kg
DM
)1 h3 h24 h72 h
Figure 5.1 Zn extraction results vs. citric acid additions for Sludge A
In the comparison of the citric acid application with conventional method, citric
acid application was found to be more effective than HF + HClO4 for Zn extraction
of the sample. Increases in extraction time have led to enhancements in the
efficiencies for all citric acid concentrations. For example, 55 455 mg/kg, 67 287
mg/kg, 77 092 mg/kg, and 78 971 mg/kg were achieved at 1 h, 3 h, 24 h, and 72 h
extraction time, respectively, when 5 mol citric acid was applied.
Oxalic Acid Results
1 mol, 2 mol, and 5 mol oxalic acid (C2H2O4) were examined for the extraction of
Zn from Sludge A. Figure 5.2 shows the extraction results of these experiments. On
the contrary to citric acid results, oxalic acid was not effective reagent for Zn
extraction except for 1 mol oxalic acid at 1 hour extraction time. The conventional
HF + HClO4 digestion method produced better results than the oxalic acid extraction.
Therefore, the oxalic acid reagent is not preferred for the exctration of Zn from
Sludge A.
51
0
10000
20000
30000
40000
50000
60000
70000
1mol OA 2 mol OA 5 mol OA HF+HClO4
Extraction Reagent
Ext
ract
ed Z
n (m
g/kg
DM
)1 h3 h24 h72 h
Figure 5.2 Zn extraction results vs. oxalic acid additions for Sludge A
As a conclusion, citric acid is more effective organic acid reagent than oxalic acid
for Zn removal from Sludge A. Besides, when comparing with inorganic acid result,
citric acid is shown up a successful reagent as well as HF + HClO4.
5.1.2 Copper Extraction Studies
Citric Acid Results
1 mol, 2 mol, and 5 mol citric acid and HF + HClO4 digestion methods were
applied for Cu removal from Sludge A. Results of these experiments are plotted in
Figure 5.3.
52
0
1
2
3
4
5
6
7
8
1 mol CA 2 mol CA 5 mol CA HF+HClO4
Extraction Reagent
Ext
ract
ed C
u (m
g/kg
DM
)1 h3 h24 h72 h
Figure 5.3 Cu extraction results vs. citric acid additions for Sludge A
Among the applications, the most succesful result was obtained at 1 hour
extraction time with 2 mol citric acid. Moreover, the extraction efficiency of Cu at 1
day extraction time with 5 mol citric acid is higher than inorganic acid (HF + HClO4)
application. Conversely, 1 mol citric acid application did not affect the extraction
efficiency as high as the others. It could not be obtained consistent results while the
extraction times were changed. It was not found any linear relationship between the
time and the efficiency at this application. When 1 mol citric acid was used,
efficiency increased with increasing extraction time; however, removal efficiency
decreased while extraction time increased in the case of 2 mol citric acid was
applied.
Oxalic Acid Results
In order to evaluate the effect of oxalic acid application on Cu extraction from
Sludge A, three different oxalic acid concentrations were used as 1, 2, and 5 mol,
respectively. The results of these experiments are given in Figure 5.4. As noted from
this figure, Cu extraction with oxalic acid was only effective when 1 mol oxalic acid
53
was used at 1 hour of extraction time. Even though very high extraction efficiency
was obtained with this application, other applications did surprisingly not yield any
effectual results for Cu extraction. On the other hand, 1 mol oxalic acid application at
1 hour was as effective as HF + HClO4 application. However, the result is not
satisfactory to use oxalic acid reagent for extraction of Cu from Sludge A.
0
1
2
3
4
5
1mol OA 2 mol OA 5 mol OA HF+HClO4
Extraction Reagent
Ext
ract
ed C
u (m
g/kg
DM
)
1 h3 h24 h72 h
Figure 5.4 Cu extraction results vs. oxalic acid additions for Sludge A
In brief, it can be said that citric acid application is more successful than oxalic
acid application for Cu removal from Sludge A. Consequently, it could be made a
preference between citric acid and conventional method from the economical point
view of in the removal of Cu from Sludge A.
5.1.3 Nickel Extraction Studies
Citric Acid Results
To assess the effeciency of citric acid for Ni removal from Sludge A, citric acid
with three different concentrations as 1 mol, 2 mol, and 5 mol was applied. The
results of citric acid and HF + HClO4 applications are shown in Figure 5.5.
54
0200400600800
100012001400160018002000
1 mol CA 2 mol CA 5 mol CA HF+HClO4
Extraction Reagent
Ext
ract
ed N
i (m
g/kg
DM
)
1 h3 h24 h72 h
Figure 5.5 Ni extraction results vs. citric acid additions for Sludge A
The experimental results have demonstrated that the citric acid was as effective
as HF + HClO4 digestion method. The maximum extraction efficiency for Ni was
obtained at 3 days extraction time with 2 mol citric acid (1 822 mg/kg Ni was
measured), but there was no colossal difference between the efficiencies of citric acid
application and HF + HClO4 digestion (1 820 mg/kg Ni was measured). As can be
seen from Figure 5.5, extraction efficiencies increased with the increasing extraction
time. For instance, 1 652 mg/kg, 1 692 mg/kg, 1 722 mg/kg, and 1 822 mg/kg Ni
were measured for 1 h, 3 h, 24 h, and 72 h of extraction time for 2 mol citric acid
application, respectively.
Oxalic Acid Results
1 mol, 2 mol, and 5 mol oxalic acid concentrations were applied to assess the
effect of oxalic acid for Ni extraction from Sludge A. Oxalic acid performances are
given in Figure 5.6 together with HF + HClO4 application performance. From this
figure, it is clearly seen that Ni extraction with oxalic acid was only effective at 1
hour extraction time with 1 mol oxalic acid as in Cu extraction studies. The
extraction efficiency for Ni is quite low as compare with inorganic acid application
55
for the other concentrations of oxalic acid. The maximum Ni removal efficiency was
achieved with HF + HClO4 extraction reagent (1 820 mg Ni/kg DM). It is therefore
more reasonable to use inorganic acid extraction for Ni removal from Sludge A.
If oxalic acid is preferred for Ni extraction, required reaction time should be taken
into consideration. Depending on the experiments, it was found that the efficiency
was inversely proportional to the extraction time.
0200400600800
100012001400160018002000
1mol OA 2 mol OA 5 mol OA HF+HClO4
Extraction Reagent
Ext
ract
ed N
i (m
g/kg
DM
)
1 h3 h24 h72 h
Figure 5.6 Ni extraction results vs. oxalic acid additions for Sludge A
5.1.4 Iron Extraction Studies
Citric Acid Results
In the comparison of citric acid application to the HF + HClO4 extraction method,
it is noticeable that Fe extraction efficiency with citric acid is rather lower at all
applications (Figure 5.7). Although maximum 15 211 mg/kg Fe was extracted among
the all citric acid concentrations, 92 220 mg/kg Fe was obtained in the case of
inorganic acid was applied.
56
0100002000030000400005000060000700008000090000
100000
1 mol CA 2 mol CA 5 mol CA HF+HClO4
Extraction Reagent
Ext
ract
ed F
e (m
g/kg
DM
)1 h3 h24 h72 h
Figure 5.7 Fe extraction results vs. citric acid additions for Sludge A
Oxalic Acid Results
Fe removal from Sludge A was also examined with oxalic acid addition and the
results are illustrated in Figure 5.8. Although oxalic acid gave high extraction
efficiency (40 031 mg Fe/kg DM) at 24 h extraction time with 5 mol concentration,
very low extraction performance was obtained with the other applications. Inorganic
acid was more effective than oxalic acid for Fe extraction from Sludge A, as in citric
acid practices.
As a concequence, oxalic acid is more effective than citric acid for iron removal
form Sludge A, as organic acid. However, HF + HClO4 digestion method is the most
appropriate method for Fe extraction; therefore, inorganic acid should be preferred
rather than organic acids.
57
0100002000030000400005000060000700008000090000
100000
1mol OA 2 mol OA 5 mol OA HF+HClO4
Extraction Reagent
Ext
ract
ed F
e (m
g/kg
DM
)
1 h3 h24 h72 h
Figure 5.8 Fe extraction results vs. oxalic acid additions for Sludge A
5.2 Results of Experimental Studies with Sludge B
Sludge B as in sludge cake form was taken successively a mechnical dewatering
unit of a dyestuff industry wastewater treatment plant. The characteristics of the
sludge sample are given in Chapter 4 (Table 4.2). To investigate the heavy metal
removal from this type of sludge, organic acids (citric acid, oxalic acid) and
inorganic acid (HF + HClO4) were examined as in Sludge A experiments. This
subsection gives the experimental results in detail. The extraction of heavy metals
with organic acids for Sludge B was performed at 1 h (0,04 d), 3 h (0,125 d), 24 h (1
d), and 72 h (3 d) of extraction time.
5.2.1 Zinc Extraction Studies
Citric Acid Results
The effect of citric acid on Zn removal from Sludge B can be seen from Figure
5.9. It is obviously apparent that 2 mol and 5 mol of citric acid applications were
quite better than HF + HClO4. Maximum Zn removal efficiency was obtained at 24 h
58
extraction time with 5 mol citric acid application. pH of the solution ranged from 2 to
4, and lowest pH value as 2 belonging to 5 mol citric acid application. Lower pH
values have led to higher efficiency, which indicates the importance of pH on
extraction process with organic acids. Increases in citric acid concentrations have
also enhanced the removal efficiency.
0
10000
20000
30000
40000
50000
60000
1 mol CA 2 mol CA 5 mol CA HF+HClO4
Extraction Reagent
Ext
ract
ed Z
n (m
g/kg
DM
)
1 h3 h24 h72 h
Figure 5.9 Zn extraction results vs. citric acid additions for Sludge B
Oxalic Acid Results
Results of oxalic acid experiments for Zn extraction are shown in Figure 5.10. 5
mol oxalic acid applications at 1 h reaction time seem to be the most efficient
experiment. Due to the other experiments are not successful as it is, the maximum
removal can not be seen as considerable result and it should be negligible. That is
why inorganic acid should effectively be used for Zn extraction from Sludge B.
59
0
10000
20000
30000
40000
50000
60000
1mol OA 2 mol OA 5 mol OA HF+HClO4
Extraction Reagent
Ext
ract
ed Z
n (m
g/kg
DM
)1 h3 h24 h72 h
Figure 5.10 Zn extraction results vs. oxalic acid additions for Sludge B
As a conclusion, citric acid could be priorly preferred to remove Zn from Sludge
B. If it is not suitable to use citric acid, HF + HClO4 digestion can be choosen.
Oxalic acid is ineffective extraction reagent for Zn removal from Sludge B.
5.2.2 Copper Extraction Studies
Citric Acid Results
The highest Cu extraction efficiency (950 mg Cu/kg DM) was achieved at 72 h
extraction time with 5 mol citric acid addition. At 1 mol and 2 mol citric acid
additions, almost Cu extraction could not be obtained. At 5 mol citric acid addition,
increasing removal efficiency was obtained with the increasing extraction time.
When comparing citric acid and inorganic acid digestion methods (311 mg Cu/kg
DM), citric acid extraction application produced three times better results than
conventional method (Figure 5.11).
60
0100200300400500600700800900
1000
1 mol CA 2 mol CA 5 mol CA HF+HClO4
Extraction Reagent
Ext
ract
ed C
u (m
g/kg
DM
)1 h3 h24 h72 h
Figure 5.11 Cu extraction results vs. citric acid additions for Sludge B
Oxalic Acid Results
Figure 5.12 summarizes the experimental results of Cu removal with different
amounts of oxalic acid additions. Similar results were also obtained with citric acid.
Experimental results have shown that the oxalic acid was more efficient than HF +
HClO4 digestion at higher extraction time and higher extraction reagent
concentrations. The maximum removal efficiency was obtained at 24 h extraction
time with 5 mol oxalic acid addition (565 mg Cu/kg DM).
As a summary, it can be said that organic acid extraction method at higher
extraction reagent concentrations and higher extraction time is more effectual than
HF + HClO4 digestion. Consequently, citric acid could be first choosen to remove Cu
from Sludge B. Oxalic acid additions could be also used for the same purpose; but, it
is not expected the results would be as succesfull as citric acid application.
61
0
100
200
300
400
500
600
1mol OA 2 mol OA 5 mol OA HF+HClO4
Extraction Reagent
Ext
ract
ed C
u (m
g/kg
DM
)
1 h3 h24 h72 h
Figure 5.12 Cu extraction results vs. oxalic acid additions for Sludge B
5.2.3 Nickel Extraction Studies
Citric Acid Results
Results of citric acid application for Ni removal from Sludge B are given in
Figure 5.13. Citric acid is very successful as it is for Sludge A. It is observed that
higher extraction times and citric acid concentrations have commonly led to
increases in the removal efficiencies. The results obtained with citric acid application
at especially high concentrations are close to the result of HF + HClO4 digestion
application. Besides, Figure 5.13 shows that 5 mol citric acid addition at 24 h
extraction time has more effectual than HF + HClO4.
62
0
50
100
150
200
250
300
1 mol CA 2 mol CA 5 mol CA HF+HClO4
Extraction Reagent
Ext
ract
ed N
i (m
g/kg
DM
)1 h3 h24 h72 h
Figure 5.13 Ni extraction results vs. citric acid additions for Sludge B
Oxalic Acid Results
Figure 5.14 illutrates the effects of oxalic acid and HF + HClO4 application on Ni
removal from Sludge B. It can be said that the oxalic acid application is not as
effective as HF + HClO4 for Ni extraction from Sludge B. Although, the most
efficient result was achieved at 1 hour extraction time with 5 mol oxalic acid, HF +
HClO4 digestion method gave similar result.
In consequence, citric acid and HF + HClO4 applications are more effective than
oxalic acid for Ni removal from Sludge B. Therefore, by considering economical
feasibilities, inorganic acid digestion or citric acid extraction should be used for this
purpose.
63
0
50
100
150
200
250
300
350
1mol OA 2 mol OA 5 mol OA HF+HClO4
Extraction Reagent
Ext
ract
ed N
i (m
g/kg
DM
)
1 h3 h24 h72 h
Figure 5.14 Ni extraction results vs. oxalic acid additions for Sludge B
5.2.4 Chromium Extraction Studies
Citric Acid Results
Figure 5.15 shows the results of chromium extraction studies with different
amounts of citric acid additions. As noted from this figure, the conventional
inorganic acid digestion method is more effective than citric acid extraction
application. While maximum 305 mg Cr could be extracted from dried sludge with
citric acid application, 694 mg Cr/ kg DM was obtained with HF+HClO4 addition.
64
0
100
200
300
400
500
600
700
800
1 mol CA 2 mol CA 5 mol CA HF+HClO4
Extraction Reagent
Ext
ract
ed C
r (m
g/kg
DM
)
1 h3 h24 h72 h
Figure 5.15 Cr extraction results vs. citric acid additions for Sludge B
Oxalic Acid Results
As can be seen from Figure 5.16, oxalic acid is not successful for Cr extraction
from Sludge B, like citric acid. However, the performance of oxalic acid was slightly
lower than citric acid. Increases in oxalic acid concentrations have led to better
efficienciens. Cr extraction could not be acquired at 1 mol and 2 mol of oxalic acid
additions; even though, Cr extraction at 1 mol acid addition was almost zero. The
most efficienct extraction was achieved at 72 h of extraction times for 5 mol oxalic
acid (336 mg Cr/kg) addition.
65
0
100
200
300
400
500
600
700
800
1mol OA 2 mol OA 5 mol OA HF+HClO4
Extraction Reagent
Ext
ract
ed C
r (m
g/kg
DM
)
1 h3 h24 h72 h
Figure 5.16 Cr extraction results vs. oxalic acid additions for Sludge B
In brief, when comparing the both organic acids with inorganic acid, the effects of
organic acids were rather low. Therefore, HF+HClO4 digestion method should be
used for the removal of Cr from Sludge B.
5.2.5 Iron Extraction Studies
Citric Acid Results
Fe removal studies from Sludge B were carried out with 1 mol, 2 mol, and 5 mol
citric acid additions and the results are given in Figure 5.17. Approximately 80 000
mg Fe/kg DS was extracted in the case of inorganic acid addition. However,
maximum 19 825 mg Fe/kg DS, 49 860 mg Fe/kg DS, and 63 718 mg Fe/kg DS
could be removed with 1 mol, 2 mol, and 5 mol of citric acid additions, respectively.
66
0
10000
20000
30000
40000
50000
60000
70000
80000
90000
1 mol CA 2 mol CA 5 mol CA HF+HClO4
Extraction Reagent
Ext
ract
ed F
e (m
g/kg
DM
)
1 h3 h24 h72 h
Figure 5.17 Fe extraction results vs. citric acid additions for Sludge B
Oxalic Acid Results
Results of oxalic acid application for Fe removal from Sludge B are shown in
Figure 5.18. While there is no effect of 1 mol oxalic acid application, the application
of 2 mol oxalic acid has slightly better effect on the removal of Fe. But, the
extraction with 5 mol oxalic acid gave superior results than the others. In particular,
the most effective value for this addition was obtained at 1 hour of extraction time.
At this application, almost the same extraction efficiency was achieved with
inorganic acid.
67
0100002000030000400005000060000700008000090000
1mol OA 2 mol OA 5 mol OA HF+HClO4
Extraction Reagent
Ext
ract
ed F
e (m
g/kg
DM
)
1 h3 h24 h72 h
Figure 5.18 Fe extraction results vs. oxalic acid additions for Sludge B
In conclusion, oxalic acid at high concentrations should be preferred instead of
citric acid as organic acid for Fe extraction from Sludge B. When oxalic acid is used
for this aim, low extraction time should be chosen.
5.3 Results of Experimental Studies with Sludge C
Sludge C is a dewatered sludge originating from an Organized Industrial District.
The characteristics of Sludge C were given in previous Chapter (see Table 4.3). In
order to examine removal efficiencies of some heavy metals from this sludge,
organic acids (citric acid and oxalic acid) and inorganic acid (HF + HClO4) were
used as applied to other sludge samples. The extraction studies of heavy metals with
the organic acids for Sludge C were performed for 1 h (0,04 d), 3 h (0,125 d), 24 h (1
d), and 72 h (3 d) of extraction time. Evaluations of these studies are given in
following sections.
68
5.3.1 Zinc Extraction Studies
Citric Acid Results
The results belonging to Zn extraction studies utilized citric acid application are
demonstrated in Figure 5.19. Higher extraction efficiency was obtained with certain
organic acids treatment while 9 680 mg Zn could be only extracted with inorganic
acid addition. For all citric acid additions, the most effective results were achieved at
high extraction time (72 h). The lowest extraction efficiency at this extraction time
was 2 767 mg Zn in the case of 1 mol citric acid added. However, it was gone up
until 11 134 mg and 12 626 mg at 2 mol and 5 mol acid additions, respectively.
0
2000
4000
6000
8000
10000
12000
14000
1 mol CA 2 mol CA 5 mol CA HF+HClO4
Extraction Reagent
Ext
ract
ed Z
n (m
g/kg
DM
)
1 h3 h24 h72 h
Figure 5.19 Zn extraction results vs. citric acid additions for Sludge C
Oxalic Acid Results
Figure 5.20 shows the results obtained with oxalic acid application for Zn removal
from Sludge C. The highest extraction was achieved with HF + HClO4 application.
69
Oxalic acid is not effective as HF + HClO4. Maximum Zn was measured as 4 503 mg
when oxalic acid applied.
0100020003000400050006000700080009000
10000
1mol OA 2 mol OA 5 mol OA HF+HClO4
Extraction Reagent
Ext
ract
ed Z
n (m
g/kg
DM
)
1 h3 h24 h72 h
Figure 5.20 Zn extraction results vs. oxalic acid additions for Sludge C
As a conclusion, citric acid is the most effectual reagent for Zn removal from
Sludge C. Oxalic acid did not exhibit similar performance on the Zn extraction for
this sample. If Zn removal is required for any sludge that will be stored either in a
landfill or agricultural usage, citric acid extraction method should be applied.
5.3.2 Nickel Extraction Studies
Citric Acid Results
Results of Ni extractions with various concentrations of citric acid for Sludge C
are shown in Figure 5.21. HF+HClO4 digestion method yielded better results in the
comparison of citric acid application. Among the citric acid additions, the most
efficient extraction was performed at 72 h of extraction time when 5 mol citric acid
was added. This value (328 mg Ni/kg) is quite near the result obtained with
HF+HClO4 digestion method, 368 mg Ni/kg. Higher extraction times for citric acid
70
application gave better efficiencies, which comfirmed the previous results obtained
for other sludge samples.
050
100150200250300350400450
1 mol CA 2 mol CA 5 mol CA HF+HClO4
Extraction Reagent
Ext
ract
ed N
i (m
g/kg
DM
)
1 h3 h24 h72 h
Figure 5.21 Ni extraction results vs. citric acid additions for Sludge C
Oxalic Acid Results
Figure 5.22 summarizes the experimental studies carried out with oxalic acid for
the removal of Ni from Sludge C. HF+HClO4 extraction gave fairly better result than
oxalic acid application. Increased oxalic acid concentrations have enchanced the
removal efficiencies. The extraction efficiencies surprisingly decreased at higher
extraction times, in particular, after 24 h.
71
050
100150200250300350400450
1mol OA 2 mol OA 5 mol OA HF+HClO4
Extraction Reagent
Ext
ract
ed N
i (m
g/kg
DM
)
1 h3 h24 h72 h
Figure 5.22 Ni extraction results vs. oxalic acid additions for Sludge C
As a result, for removing Ni from Sludge C, organic acids are not superior
solution since the inorganic acid (HF+HClO4) extraction is more sensible method for
this purpose.
5.3.3 Chromium Extraction Studies
Citric Acid Results
The results obtained with citric acid application for Cr removal from Sludge C are
depicted in Figure 5.23. As can be seen from this figure, inorganic acid application
gave better results than citric acid additions. The maximum Cr extraction was
determined as 1 093 mg Cr/kg DM at the inorganic acid application (HF+HClO4).
It was found a linear relationship between extraction time and efficiency at citric
acid application. For example; 133 mg Cr, 352 mg Cr, 730 mg Cr, and 815 mg Cr
could be extracted at 1 h, 3 h, 24 h, and 72 h of extraction time, respectively, when 5
mol acid was used. Similarly, at 2 mol acid addition, the amount of extracted Cr
increased from 112 mg to 704 mg when extraction time increased from 1 h to 3 days.
72
On the other hand, higher citric acid concentrations improved the efficiency. The
best result between citric acid additions was achieved at 72 h of extraction time with
5 mol citric acid.
0
200
400
600
800
1000
1200
1 mol CA 2 mol CA 5 mol CA HF+HClO4
Extraction Reagent
Ext
ract
ed C
r (m
g/kg
DM
)
1 h3 h24 h72 h
Figure 5.23 Cr extraction results vs. citric acid additions for Sludge C
Oxalic Acid Results
The following figure shows the obtained results from oxalic acid extraction
studies of Cr from Sludge C (Figure 5.24). Oxalic acid is not satisfactorily effective
for Cr removal. Inorganic acid gave much better effect than oxalic acid.
As in citric acid application, increases in oxalic acid concentrations improved the
removal efficiency. More effective results were obtained for the highest oxalic acid
addition (5 mol) comparing with the other concentrations.
73
0
200
400
600
800
1000
1200
1mol OA 2 mol OA 5 mol OA HF+HClO4
Extraction Reagent
Ext
ract
ed C
r (m
g/kg
DM
)
1 h3 h24 h72 h
Figure 5.24 Cr extraction results vs. oxalic acid additions for Sludge C
Consequently, Cr extraction with organic acids from Sludge C is not reasonable.
Anyhow, if organic acids preferred, high extraction time should be required. But, the
most suitable method for this purpose is inorganic acid digestion.
5.3.4 Iron Extraction Studies
Citric Acid Results
Figure 5.25 depicts the results of experimental studies of Fe extractions with
various concentrations of citric acid for Sludge C. The maximum Fe extraction (77
368 mg) could be obtained using 5 mol citric acid at 24 h of extraction time.
Following this, the best result was 75 412 mg Fe for 2 mol acid application at 72 h of
extraction time. The experimental studies have showed that increasing citric acid
concentrations have led to improved extraction efficiencies.
74
0
10000
2000030000
40000
50000
6000070000
80000
90000
1 mol CA 2 mol CA 5 mol CA HF+HClO4
Extraction Reagent
Ext
ract
ed F
e (m
g/kg
DM
)1 h3 h24 h72 h
Figure 5.25 Fe extraction results vs. citric acid additions for Sludge C
Oxalic Acid Results
As in citric acid application, oxalic acid application is also not effective for
removal of Fe from Sludge C (Figure 5.26) at low concentrations (1 mol and 2 mol).
However, more successful results were obtained at 5 mol acid addition. Especially
higher extraction times at 5 mol addition caused much more Fe removal from Sludge
C. Although 83 940 mg Fe could be removed with inorganic acid, 5 mol oxalic acid
at 72 h of extraction time gave the best removal as over than 90 000 mg Fe.
Although higher extraction times increased the extraction efficiency at 5 mol
citric acid addition, it was ascertained that reverse relationship was found between
extraction time and removal efficiency at lower oxalic acid concentrations.
75
0100002000030000400005000060000700008000090000
100000
1mol OA 2 mol OA 5 mol OA HF+HClO4
Extraction Reagent
Ext
ract
ed F
e (m
g/kg
DM
)
1 h3 h24 h72 h
Figure 5.26 Fe extraction results vs. oxalic acid additions for Sludge C
As a result, organic acids, both citric and oxalic, or inorganic acid (HF+HClO4)
should be used for Fe extraction from Sludge C. In the case of organic acids are
preferred for this aim, higher acid concentrations and higher extraction times should
be applied.
5.3.5 Copper Extraction Studies
Citric Acid Results
Figure 5.27 shows the results obtained with citric acid for Cu removal from
Sludge C. Surprisingly, any effects of citric acids on Cu extractions were detected at
the applied experimental conditions.
76
0
100
200
300
400
500
600
700
800
1 mol CA 2 mol CA 5 mol CA HF+HClO4
Extraction Reagent
Ext
ract
ed C
u (m
g/kg
DM
)
1 h3 h24 h72 h
Figure 5.27 Cu extraction results vs. citric acid additions for Sludge C
Oxalic Acid Results
Oxalic acid additions were also not effective of Cu removal from Sludge C as in
citric acid experiments. A small amount of Cu could be extracted from the sludge at
only 5 mol oxalic acid applications (Figure 5.28).
0100200300400500600700800
1mol OA 2 mol OA 5 mol OA HF+HClO4
Extraction Reagent
Ext
ract
ed C
u (m
g/kg
DM
)
1 h3 h24 h72 h
Figure 5.28 Cu extraction results vs. oxalic acid additions for Sludge C
77
In brief, it is questionably understood that organic acids are not effective for Cu
removal from Sludge C. In comparison of inorganic acid method with organic acids,
HF+HClO4 digestion method is very effective. Therefore, HF+HClO4 elutriation
method should be used for this purpose.
5.4 Results of Experimental Studies with Sludge D
Sludge D is a dewatered sludge originating from a metal industry, which is
different from the sources of Sludge A. The characteristics of Sludge D were given in
previous Chapter (see Table 4.4). Effects of organic acids (citric, oxalic, and acetic)
and inorganic acid (HF+HClO4) on several heavy metal extractions from sludge D
were investigated and results of these studies are discussed below. At this study,
acetic acid was also examined different from previous studies carried out with
Sludge A, B, and C.
5.4.1 Zinc Extraction Studies
Citric Acid Results
The following figure shows the effect of citric acid on Zn removal from Sludge D
(Figure 5.29). When comparing citric acid and HF+HClO4 digestion methods, citric
acid extraction application produced about eight times lower extraction efficiencies
than inorganic acid digestion method.
78
0
1000
2000
3000
40005000
6000
7000
8000
9000
1 mol CA 2 mol CA 5 mol CA HF+HClO4
Extraction Reagent
Ext
ract
ed Z
n (m
g/kg
DM
)1 h3 h24 h72 h
Figure 5.29 Zn extraction results vs. citric acid additions for Sludge D
Oxalic Acid Results
Figure 5.30 summarizes the experimental results of Zn removal from Sludge D
with different amounts of oxalic acid additions. At this application, almost the same
extraction efficiency was achieved with citric acid. Higher than 8 000 mg Zn was
extracted with HF+HClO4, while lower than 1 000 mg Zn could be only extracted
with oxalic acid additions.
79
0100020003000400050006000700080009000
10000
1mol OA 2 mol OA 5 mol OA HF+HClO4
Extraction Reagent
Ext
ract
ed Z
n (m
g/kg
DM
)1 h3 h24 h72 h
Figure 5.30 Zn extraction results vs. oxalic acid additions for Sludge D
Acetic Acid Results
Figure 5.31 shows the results of experimental studies carried out with acetic acid
for Zn removal from Sludge D. The experimental results have demonstrated that the
acetic acid was not effective as in citric and oxalic acid applications. But, acetic acid
is most effective extraction reagent among the applied organic acids. Higher
extraction times for citric acid application gave better Zn extraction efficiencies at all
acetic acid additions.
80
0100020003000400050006000700080009000
10000
1 mol Ac 2 mol Ac 5 mol Ac HF+HClO4
Extraction Reagent
Ext
ract
ed Z
n (m
g/kg
DM
)
1 h3 h24 h72 h
Figure 5.31 Zn extraction results vs. acetic acid additions for Sludge D
As a conclusion, organic acids application is not good alternative for Zn
extraction from Sludge D. Inorganic acid digestion method is the most ideal solution
for Zn removal from Sludge D.
5.4.2 Nickel Extraction Studies
Citric Acid Results
The following figure shows the obtained results from citric acid extraction studies
of Ni from Sludge D (Figure 5.32). The maximum extraction efficiency was
achieved with inorganic acid. Although increases in the extraction time and the
concentration of acid have led to increases in the efficiencies, very low extraction
performance was obtained with the citric acid additions.
81
0
20
40
60
80
100
120
140
160
1 mol CA 2 mol CA 5 mol CA HF+HClO4
Extraction Reagent
Ext
ract
ed N
i (m
g/kg
DM
)
1 h3 h24 h72 h
Figure 5.32 Ni extraction results vs. citric acid additions for Sludge D
Oxalic Acid Results
Figure 5.33 depicts the results of experimental studies of Ni extractions with
various concentrations of oxalic acid for Sludge D. Increases in both the extraction
time and the oxalic acid concentration have led to increases in the efficiencies. But,
the highest extraction efficiency of oxalic acid is lower than the extraction efficiency
obtained with inorganic acid. As a result of the study, if oxalic acid is used for Ni
extraction, high amount of oxalic acid concentrations and high extraction time should
be chosen.
82
0
20
40
60
80
100
120
140
160
1mol OA 2 mol OA 5 mol OA HF+HClO4
Extraction Reagent
Ext
ract
ed N
i (m
g/kg
DM
)
1 h3 h24 h72 h
Figure 5.33 Ni extraction results vs. oxalic acid additions for Sludge D
Acetic Acid Results
Figure 5.25 depicts the results of experimental studies of Ni extractions with
various concentrations of acetic acid for Sludge D. Acetic acid additions gave more
successful results than HF+HClO4 reagent. Increasing removal efficiency was
obtained with the increasing extraction time.
0
50
100
150
200
250
300
1 mol Ac 2 mol Ac 5 mol Ac HF+HClO4
Extraction Reagent
Ext
ract
ed N
i (m
g/kg
DM
)
1 h3 h24 h72 h
Figure 5.34 Ni extraction results vs. acetic acid additions for Sludge D
83
As a result, among other organic acids and inorganic acid applications, acetic acid
gave higher extraction efficiency. Therefore, it could be preferred for removal of Ni
from Sludge D.
5.4.3 Copper Extraction Studies
Citric Acid Results
Figure 5.35 summarizes the results of experimental studies of Cu removal with
different amounts of citric acid additions. From this figure, it is clearly seen that Cu
extraction with inorganic acid produced five times better results than citric acid
extraction for Sludge D. At all citric acid applications, 3 h of extraction time gave the
best result.
0
50
100
150
200
250
1 mol CA 2 mol CA 5 mol CA HF+HClO4
Extraction Reagent
Ext
ract
ed C
u (m
g/kg
DM
)
1 h3 h24 h72 h
Figure 5.35 Cu extraction results vs. citric acid additions for Sludge D
Oxalic Acid Results
As in citric acid addition, oxalic acid was not successful for Cu extraction from
Sludge D. The extraction efficiency of oxalic acid at applied conditions for Cu is
84
quite low as compare with inorganic acid application. HF+HClO4 digestion method
gave better result than oxalic acid additions like citric acid.
0
50
100
150
200
250
1mol OA 2 mol OA 5 mol OA HF+HClO4
Extraction Reagent
Ext
ract
ed C
u (m
g/kg
DM
)
1 h3 h24 h72 h
Figure 5.36 Cu extraction results vs. oxalic acid additions for Sludge D
Acetic Acid Results
Figure 5.37 summarizes the results of experimental studies of Cu removal with
different amounts of acetic acid additions. As in Ni extraction studies, acetic acid
gave the best results among organic acid applications. The maximum Cu extraction
was obtained at 3 h extraction time with 2 mol acetic acid addition (128 mg Cu/kg).
As a conclusion, HF+HClO4 digestion method is the best extraction method for
Cu removal from Sludge D. In the case of organic acids are preferred for this aim,
acetic acid should be choosen.
85
0
50
100
150
200
250
1 mol Ac 2 mol Ac 5 mol Ac HF+HClO4
Extraction Reagent
Ext
ract
ed C
u (m
g/kg
DM
)1 h3 h24 h72 h
Figure 5.37 Cu extraction results vs. acetic acid additions for Sludge D
5.4.4 Lead Extraction Studies
Citric Acid Results
Performances of citric acid on Pb removal form Sludge D are shown in Figure
5.38. Surprisingly, any effects of 1 mol citric acids and HF+HClO4 on Pb extractions
were detected at the applied experimental conditions. However, 2 mol and 5 mol
citric acid additions could be extracted Pb from Sludge D. It was not found any linear
relationship between the extraction time and the extraction efficiency at this
application. The highest Pb concentration was measured at 1 hour extraction time
with 5 mol citric acid addition (about 180 mg Pb/kg DS).
86
020406080
100120140160180200
1 mol CA 2 mol CA 5 mol CA HF+HClO4
Extraction Reagent
Ext
ract
ed P
b (m
g/kg
DM
)1 h3 h24 h72 h
Figure 5.38 Pb extraction results vs. citric acid additions for Sludge D
Oxalic Acid Results
The high concentrations of oxalic acid additions were more effective for Pb
extraction from Sludge D as it is seen from Figure 5.39. The highest performance
was obtained at 24 h of extraction time with 5 mol oxalic acid addition (135 mg
Pb/kg DS) and this result is lower than the maximum result obtained with citric acid.
It was not ascertained any linear relationship between the extraction time and the
extraction efficiency.
87
020
406080
100120
140160
1mol OA 2 mol OA 5 mol OA HF+HClO4
Extraction Reagent
Ext
ract
ed P
b (m
g/kg
DM
)1 h3 h24 h72 h
Figure 5.39 Pb extraction results vs. oxalic acid additions for Sludge D
Acetic Acid Results
Figure 5.40 depicts the results of Pb extraction studies with various concentrations
of acetic acid for Sludge D. Acetic acid was very successful for Pb removal. The best
result (436 mg Pb/kg DS) was obtained at 72 h of extraction time with 1 mol acetic
acid addition.
050
100150200250300350400450500
1 mol Ac 2 mol Ac 5 mol Ac HF+HClO4
Extraction Reagent
Ext
ract
ed P
b (m
g/kg
DM
)
1 h3 h24 h72 h
Figure 5.40 Pb extraction results vs. acetic acid additions for Sludge D
88
As a result, organic acid is more succesfull extraction reagent comparing with
inorganic acid for Pb removal from Sludge D. It was found that, acetic acid is the
most effective acid among applied organic acids.
5.4.5 Iron Extraction Studies
Citric Acid Results
The results of Fe extraction studies carried out with citric acid are given in Figure
5.41. The citric acid additions were not effective as HF+HClO4 as. Increases in
extraction time and acid concentration have led to enhancements in the efficiencies at
all citric acid concentrations. The most extraction efficiency was obtained at 72 h
extraction time with 5 mol citric acid addition (837 mg Fe/kg DS).
0
500
1000
1500
2000
2500
1 mol CA 2 mol CA 5 mol CA HF+HClO4
Extraction Reagent
Ext
ract
ed F
e (m
g/kg
DM
)
1 h3 h24 h72 h
Figure 5.41 Fe extraction results vs. citric acid additions for Sludge D
Oxalic Acid Results
Although the oxalic acid additions gave similar results with citric acid for Fe
removal from Sludge D (Figure 5.42), the maximum Fe extraction efficiency
89
obtained with oxalic acid (657 mg Fe/kg DS) was lower than the maximum of citric
acid (837 mg Fe/kg DS).
0
500
1000
1500
2000
2500
1mol OA 2 mol OA 5 mol OA HF+HClO4Extraction Reagent
Ext
ract
ed F
e (m
g/kg
DM
)
1 h3 h24 h72 h
Figure 5.42 Fe extraction results vs. oxalic acid additions for Sludge D
Acetic Acid Results
The following figure shows the obtained results from 1 mol, 2 mol, and 5 mol
acetic acid extraction studies of Fe from Sludge D (Figure 5.43). The best extraction
efficiency was obtained at 72 h of extraction time with 1 mol acetic acid addition. It
is seen from this figure that increases in acetic acid concentration have decreased the
efficiency. Moreover, in some cases acetic acid affected the extraction efficiency
better than inorganic acid application.
90
0500
100015002000250030003500400045005000
1 mol Ac 2 mol Ac 5 mol Ac HF+HClO4
Extraction Reagent
Ext
ract
ed F
e (m
g/kg
DM
)1 h3 h24 h72 h
Figure 5.43 Fe extraction results vs. acetic acid additions for Sludge D
In conclusion, acetic acid is the most suitable extraction reagent among the
examined acids for Fe extraction from Sludge D and it could be preferred rather than
citric, oxalic and HF+HClO4 application.
5.4.6 Cadmium Extraction Studies
Citric Acid Results
Similar to Pb extraction, HF+HClO4 digestion method was not responsible for Cd
extraction from Sludge D. However, citric acid is also effective at only three
experimental studies. The most efficient removal (3,55 mg Cd/kg DS) was achieved
at 1 hour extraction time with 5 mol citric acid, but at 72 h of extraction time with 1
mol acid gave comparable result with it.
91
0
1
2
3
4
1 mol CA 2 mol CA 5 mol CA HF+HClO4
Extraction Reagent
Ext
ract
ed C
d (m
g/kg
DM
)
1 h3 h24 h72 h
Figure 5.44 Cd extraction results vs. citric acid additions for Sludge D
Oxalic Acid Results
Figure 5.45 shows the results achieved with oxalic acid for Cd removal from
Sludge D. The highest result (6,35 mg Cd/kg DS) was achieved at 1 hour extraction
time with 2 mol oxalic acid.
0
1
2
3
4
5
6
7
1mol OA 2 mol OA 5 mol OA HF+HClO4
Extraction Reagent
Ext
ract
ed C
d (m
g/kg
DM
)
1 h3 h24 h72 h
Figure 5.45 Cd extraction results vs. oxalic acid additions for Sludge D
92
Acetic Acid Results
Acetic acid effects on the removal of Cd are shown in Figure 5.46. Particularly, in
the application of 1 mol acetic acid, the best extraction efficiencies were obtained.
The best Cd extraction (32 mg Cd/kg DS) with acetic acid was obtained at 72 h of
extraction time when 1 mol acetic acid was applied.
0
5
10
15
20
25
30
35
1 mol Ac 2 mol Ac 5 mol Ac HF+HClO4
Extraction Reagent
Ext
ract
ed C
d (m
g/kg
DM
)
1 h3 h24 h72 h
Figure 5.46 Cd extraction results vs. acetic acid additions for Sludge D
In brief, the value obtained with acetic acid is about seven times more than citric
acid. 3,55 mg, 6,35 mg, and 32 mg Cd could be extracted with citric, oxalic, and
acetic acid application, respectively. Therefore, acetic acid should be preferred for
Cd removal from Sludge D.
5.5. Cost Analysis
The cost analyses of applied extraction methods were also performed. The costs
were calculated on unit dry matter of sludge and unit analysis.
93
The costs were calculated based on chemical material consumptions. The result of
this study will be useful to assess the potential value for application of extraction
processes at a full-scale plant.
Table 5.1 gives the cost analyses results and it is seen from the table that HF +
HClO4 digestion method is the most expensive method following by acetic acid,
oxalic acid, and citric acid addition. Veeken (1999) reported that inorganic acids and
complexing agents are not applicable on a practical scale due to the costs of the
process. The cost analyses of this study also confirm this result.
Table 5.1 Cost analysis of the extraction methods used this study.
Method Cost ($/kg DM) Cost ($/analysis)
HF + HClO4 560 0,28
Citric Acid 24 0,12
Oxalic Acid 32 0,16
Acetic Acid 48 0,24
94
CHAPTER SIX
CONCLUSIONS AND RECOMMENDATIONS
6.1. Conclusions
The aim of this study was to investigate the effects of inorganic and organic acids
on extraction of heavy metals from treatment plant sludges. For this purpose, four
different industrial sludges were taken from a dyestuff industry, two metal industries,
and an organized industrial district. After characterization of raw sludges, extraction
studies were carried out with inorganic acid (HF+HClO4) and organic acids (citric
acid, oxalic acid, and acetic acid). In extraction studies with organic acids, three
different concentrations of acids (1 mol, 2 mol, and 5 mol) and four extraction times
(1 h, 3 h, 24 h, and 72 h) were examined.
According to the experimental results, the conclusion remarks from this study
could be given as follows:
• Citric acid is more effective organic acid reagent than oxalic acid for Zn
removal from Sludge A. Besides, when comparing with inorganic acid results,
citric acid is shown up a successful reagent as well as HF + HClO4.
• Citric acid application is more successful than oxalic acid application for Cu
removal from Sludge A. Consequently, it could be made a preference between
citric acid and conventional method from the economical point view of in the
removal of Cu from Sludge A.
• The maximum Ni removal efficiency from Sludge A was achieved with HF +
HClO4 extraction reagent (1 820 mg Ni/kg DM). The experimental results have
demonstrated that the citric acid was also as effective as HF + HClO4 digestion
method.
• Oxalic acid is more effective than citric acid for iron removal form Sludge A.
However, HF + HClO4 digestion method is the most appropriate method for Fe
extraction; therefore, inorganic acid should be preferred rather than organic
acids.
95
• Citric acid could be priorly preferred to remove Zn from Sludge B. If it is not
suitable to use citric acid, HF + HClO4 digestion can be chosen. Oxalic acid is
ineffective extraction reagent for Zn removal from Sludge B.
• Organic acid extraction method at higher extraction reagent concentrations and
higher extraction time is more effectual than HF + HClO4 digestion.
Consequently, citric acid could be first chosen to remove Cu from Sludge B.
Oxalic acid additions could be also used for the same purpose; but, it is not
expected the results would be as successful as citric acid application.
• Citric acid and HF + HClO4 applications are more effective than oxalic acid for
Ni removal from Sludge B. Therefore, by considering economical feasibilities,
inorganic acid digestion or citric acid extraction should be used for this
purpose.
• When comparing the both organic acids with inorganic acid, the effects of
organic acids were rather low. Therefore, HF+HClO4 digestion method should
be used for the removal of Cr from Sludge B.
• Oxalic acid at high concentrations should be preferred instead of citric acid as
organic acid for Fe extraction from Sludge B. When oxalic acid is used for this
aim, low extraction time should be chosen.
• Citric acid is the most effectual reagent for Zn removal from Sludge C. Oxalic
acid did not exhibit similar performance on the Zn extraction for this sample. If
Zn removal is required for any sludge that will be stored either in a landfill or
agricultural usage, citric acid extraction method should be applied.
• For removing Ni from Sludge C, organic acids are not superior solution since
the inorganic acid (HF+HClO4) extraction is more sensible method for this
purpose.
• Cr extraction with organic acids from Sludge C is not reasonable. Anyhow, if
organic acids preferred, high extraction time should be required. But, the most
suitable method for this purpose is inorganic acid digestion.
• Organic acids, both citric and oxalic, or inorganic acid (HF+HClO4) should be
used for Fe extraction from Sludge C. In the case of organic acids are preferred
for this aim, higher acid concentrations and higher extraction times should be
applied.
96
• It is questionably understood that organic acids are not effective for Cu
removal from Sludge C. In comparison of inorganic acid method with organic
acids, HF+HClO4 digestion method is very effective. Therefore, HF+HClO4
elutriation method should be used for this purpose.
• Organic acids application is not good alternative for Zn extraction from Sludge
D. Inorganic acid digestion method is the most ideal solution for Zn removal
from Sludge D.
• Among other organic acids and inorganic acid applications, acetic acid gave
higher extraction efficiency. Therefore, it could be preferred for removal of Ni
from Sludge D.
• HF+HClO4 digestion method is the best extraction method for Cu removal
from Sludge D. In the case of organic acids are preferred for this aim, acetic
acid should be chosen.
• Organic acid is more successful extraction reagent comparing with inorganic
acid for Pb removal from Sludge D. It was found that, acetic acid is the most
effective acid among applied organic acids.
• Acetic acid is the most suitable extraction reagent among the examined acids
for Fe extraction from Sludge D and it could be preferred rather than citric,
oxalic and HF+HClO4 application.
• The value obtained with acetic acid is about seven times more than citric acid.
Therefore, acetic acid should be preferred for Cd removal from Sludge D.
• The estimation of cost of heavy metal extraction from sludge is a part of the
research. Depending on the calculations, HF+HClO4 application is more
expensive than organic acid applications.
6.2. Recommendations
• Extraction efficiencies of organic acids should also be monitored depending on
the temperature and pH.
• Heavy metal extraction studies will also be carried out in a larger scale plant
like pilot scale or full scale plant.
97
• As acetic acid was usually more successful reagent than citric acid and oxalic
acid and because acetic acid naturally occurs during anaerobic decomposition,
heavy metal removal may be investigated in an anaerobic stabilization of
sludge containing heavy metal.
98
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103
APPENDICES
Table A 1 The results of Zn extraction carried out with citric acid for Sludge A
Extracted Zn Concentration (mg/kg DM)
at different extraction times
Citric Acid
Concentration
for kg DM 1 h 3 h 24 h 72 h
1 mol CA 6 605 59 204 66 497 64 265
2 mol CA 62 202 60 702 67 658 70 762
5 mol CA 55 455 67 287 77 092 78 971
Table A 2 The results of Zn extraction carried out with oxalic acid for Sludge A
Extracted Zn Concentration (mg/kg DM)
at different extraction times
Oxalic Acid
Concentration
for kg DM 1 h 3 h 24 h 72 h
1 mol OA 51 363 4 773 4 836 4 827
2 mol OA 796 653 104 131
5 mol OA 1 799 1 244 154 22
Table A 3 The results of Ni extraction carried out with citric acid for Sludge A
Extracted Ni Concentration (mg/kg DM)
at different extraction times
Citric Acid
Concentration
for kg DM 1 h 3 h 24 h 72 h
1 mol CA 465 1 547 1 608 1 673
2 mol CA 1 652 1 692 1 722 1 822
5 mol CA 1 345 1 415 1 455 1 706
104
Table A 4 The results of Ni extraction carried out with oxalic acid for Sludge A
Extracted Ni Concentration (mg/kg DM)
at different extraction times
Oxalic Acid
Concentration
for kg DM 1 h 3 h 24 h 72 h
1 mol OA 1 531 292 217 127
2 mol OA 160 118 23 21
5 mol OA 635 446 137 115
Table A 5 The results of Cu extraction carried out with citric acid for Sludge A
Extracted Cu Concentration (mg/kg DM)
at different extraction times
Citric Acid
Concentration
for kg DM 1 h 3 h 24 h 72 h
1 mol CA 1,16 1,5 2,1 3
2 mol CA 7 4,9 5,4 4,4
5 mol CA 3,8 0,27 5,4 1,5
Table A 6 The results of Cu extraction carried out with oxalic acid for Sludge A
Extracted Cu Concentration (mg/kg DM)
at different extraction times
Oxalic Acid
Concentration
for kg DM 1 h 3 h 24 h 72 h
1 mol OA 4,7 - - -
2 mol OA - - - -
5 mol OA - - - -
105
Table A 7 The results of Fe extraction carried out with citric acid for Sludge A
Extracted Fe Concentration (mg/kg DM)
at different extraction times
Citric Acid
Concentration
for kg DM 1 h 3 h 24 h 72 h
1 mol CA 6 733 3 200 3 683 4 200
2 mol CA 5 052 5 555 6 314 8 362
5 mol CA 7 591 7 516 6 388 15 211
Table A 8 The results of Fe extraction carried out with oxalic acid for Sludge A
Extracted Fe Concentration (mg/kg DM)
at different extraction times
Oxalic Acid
Concentration
for kg DM 1 h 3 h 24 h 72 h
1 mol OA 3 535 4 211 2 323 1 070
2 mol OA 8 487 10 274 9 122 7 112
5 mol OA 15 143 34 500 40 031 21 200
Table A 9 The results of Zn extraction carried out with citric acid for Sludge B
Extracted Zn Concentration (mg/kg DM)
at different extraction times
Citric Acid
Concentration
for kg DM 1 h 3 h 24 h 72 h
1 mol CA 18 564 18 167 16 413 9 810
2 mol CA 30 012 32 487 36 212 33 373
5 mol CA 36 723 41 469 51 410 4 898
106
Table A 10 The results of Zn extraction carried out with oxalic acid for Sludge B
Extracted Zn Concentration (mg/kg DM)
at different extraction times
Oxalic Acid
Concentration
for kg DM 1 h 3 h 24 h 72 h
1 mol OA 3 230 2 624 1 242 675
2 mol OA 15 767 16 500 10 435 3 844
5 mol OA 54 745 2 983 7 330 3 634
Table A 11 The results of Ni extraction carried out with citric acid for Sludge B
Extracted Ni Concentration (mg/kg DM)
at different extraction times
Citric Acid
Concentration
for kg DM 1 h 3 h 24 h 72 h
1 mol CA 107 130 156 156
2 mol CA 145 184 218 236
5 mol CA 190 241 285 130
Table A 12 The results of Ni extraction carried out with oxalic acid for Sludge B
Extracted Ni Concentration (mg/kg DM)
at different extraction times
Oxalic Acid
Concentration
for kg DM 1 h 3 h 24 h 72 h
1 mol OA 29 50 45 45
2 mol OA 114 105 87 72
5 mol OA 292 134 136 76
107
Table A 13 The results of Cu extraction carried out with citric acid for Sludge B
Extracted Cu Concentration (mg/kg DM)
at different extraction times
Citric Acid
Concentration
for kg DM 1 h 3 h 24 h 72 h
1 mol CA - - - -
2 mol CA - - - 96
5 mol CA 44 73 636 950
Table A 14 The results of Cu extraction carried out with oxalic acid for Sludge B
Extracted Cu Concentration (mg/kg DM)
at different extraction times
Oxalic Acid
Concentration
for kg DM 1 h 3 h 24 h 72 h
1 mol OA - - - -
2 mol OA 50 54 42 16
5 mol OA 52 82 565 460
Table A 15 The results of Cr extraction carried out with citric acid for Sludge B
Extracted Cr Concentration (mg/kg DM)
at different extraction times
Citric Acid
Concentration
for kg DM 1 h 3 h 24 h 72 h
1 mol CA 119 112 107 100
2 mol CA 195 197 226 221
5 mol CA 180 253 305 140
108
Table A 16 The results of Cr extraction carried out with oxalic acid for Sludge B
Extracted Cr Concentration (mg/kg DM)
at different extraction times
Oxalic Acid
Concentration
for kg DM 1 h 3 h 24 h 72 h
1 mol OA - - - -
2 mol OA 9 7,8 6,3 3,1
5 mol OA 24 28 227 336
Table A 17 The results of Fe extraction carried out with citric acid for Sludge B
Extracted Fe Concentration (mg/kg DM)
at different extraction times
Citric Acid
Concentration
for kg DM 1 h 3 h 24 h 72 h
1 mol CA 14 378 17 436 16 652 19 825
2 mol CA 36 254 38 192 49 860 43 731
5 mol CA 61 453 49 906 63 718 52 517
Table A 18 The results of Fe extraction carried out with oxalic acid for Sludge B
Extracted Fe Concentration (mg/kg DM)
at different extraction times
Oxalic Acid
Concentration
for kg DM 1 h 3 h 24 h 72 h
1 mol OA 84 71 51 68
2 mol OA 13 000 17 363 1620 182
5 mol OA 80 511 68 792 63 500 63 817
109
Table A 19 The results of Zn extraction carried out with citric acid for Sludge C
Extracted Zn Concentration (mg/kg DM)
at different extraction times
Citric Acid
Concentration
for kg DM 1 h 3 h 24 h 72 h
1 mol CA 1 187 1 617 1 816 2 767
2 mol CA 1 690 3 183 7 535 11 134
5 mol CA 2 981 4 412 4 295 12 626
Table A 20 The results of Zn extraction carried out with oxalic acid for Sludge C
Extracted Zn Concentration (mg/kg DM)
at different extraction times
Oxalic Acid
Concentration
for kg DM 1 h 3 h 24 h 72 h
1 mol OA 1 515 1 314 250 320
2 mol OA 3 087 3 954 4 120 1 234
5 mol OA 3 587 1 803 4 503 583
Table A 21 The results of Ni extraction carried out with citric acid for Sludge C
Extracted Ni Concentration (mg/kg DM)
at different extraction times
Citric Acid
Concentration
for kg DM 1 h 3 h 24 h 72 h
1 mol CA 107 120 160 197
2 mol CA 147 194 257 251
5 mol CA 196 264 221 328
110
Table A 22 The results of Ni extraction carried out with oxalic acid for Sludge C
Extracted Ni Concentration (mg/kg DM)
at different extraction times
Oxalic Acid
Concentration
for kg DM 1 h 3 h 24 h 72 h
1 mol OA 100 103 40 27
2 mol OA 161 184 170 50
5 mol OA 201 215 227 81
Table A 23 The results of Cu extraction carried out with citric acid for Sludge C
Extracted Cu Concentration (mg/kg DM)
at different extraction times
Citric Acid
Concentration
for kg DM 1 h 3 h 24 h 72 h
1 mol CA - - - -
2 mol CA - - - 0,59
5 mol CA - - - 0,62
Table A 24 The results of Cu extraction carried out with oxalic acid for Sludge C
Extracted Cu Concentration (mg/kg DM)
at different extraction times
Oxalic Acid
Concentration
for kg DM 1 h 3 h 24 h 72 h
1 mol OA - -- - -
2 mol OA - - - 3,26
5 mol OA - - 13 62
111
Table A 25 The results of Cr extraction carried out with citric acid for Sludge C
Extracted Cr Concentration (mg/kg DM)
at different extraction times
Citric Acid
Concentration
for kg DM 1 h 3 h 24 h 72 h
1 mol CA 81 130 290 372
2 mol CA 112 295 606 704
5 mol CA 133 352 730 815
Table A 26 The results of Cr extraction carried out with oxalic acid for Sludge C
Extracted Cr Concentration (mg/kg DM)
at different extraction times
Oxalic Acid
Concentration
for kg DM 1 h 3 h 24 h 72 h
1 mol OA 83 66 43 70
2 mol OA 172 182 207 172
5 mol OA 238 366 690 760
Table A 27 The results of Fe extraction carried out with citric acid for Sludge C
Extracted Fe Concentration (mg/kg DM)
at different extraction times
Citric Acid
Concentration
for kg DM 1 h 3 h 24 h 72 h
1 mol CA 28 284 44 450 57 650 60 208
2 mol CA 50 000 45 492 56 576 75 412
5 mol CA 34 933 56 281 77 368 67 051
112
Table A 28 The results of Fe extraction carried out with oxalic acid for Sludge C
Extracted Fe Concentration (mg/kg DM)
at different extraction times
Oxalic Acid
Concentration
for kg DM 1 h 3 h 24 h 72 h
1 mol OA 25 400 15 863 5 571 1 621
2 mol OA 34 188 17 646 27 658 15 884
5 mol OA 27 700 30 594 71 377 92 045
Table A 29 The results of Zn extraction carried out with citric acid for Sludge D
Extracted Zn Concentration (mg/kg DM)
at different extraction times
Citric Acid
Concentration
for kg DM 1 h 3 h 24 h 72 h
1 mol CA 88 145 275 285
2 mol CA 103 177 390 520
5 mol CA 93 175 464 675
Table A 30 The results of Zn extraction carried out with oxalic acid for Sludge D
Extracted Zn Concentration (mg/kg DM)
at different extraction times
Oxalic Acid
Concentration
for kg DM 1 h 3 h 24 h 72 h
1 mol OA 125 133 146 163
2 mol OA 211 231 250 295
5 mol OA 249 336 526 624
113
Table A 31 The results of Zn extraction carried out with acetic acid for Sludge D
Extracted Zn Concentration (mg/kg DM)
at different extraction times
Acetic Acid
Concentration
for kg DM 1 h 3 h 24 h 72 h
1 mol Ac 540 798 1 920 2 585
2 mol Ac 586 938 1 778 2 085
5 mol Ac 680 1 130 1 570 1 868
Table A 32 The results of Ni extraction carried out with citric acid for Sludge D
Extracted Ni Concentration (mg/kg DM)
at different extraction times
Citric Acid
Concentration
for kg DM 1 h 3 h 24 h 72 h
1 mol CA 16 18 26 32
2 mol CA 27 29 39 57
5 mol CA 69 64 85 87
Table A 33 The results of Ni extraction carried out with oxalic acid for Sludge D
Extracted Ni Concentration (mg/kg DM)
at different extraction times
Oxalic Acid
Concentration
for kg DM 1 h 3 h 24 h 72 h
1 mol OA 15 18 19 21
2 mol OA 34 35 39 41
5 mol OA 68 78 97 105
114
Table A 34 The results of Ni extraction carried out with acetic acid for Sludge D
Extracted Ni Concentration (mg/kg DM)
at different extraction times
Acetic Acid
Concentration
for kg DM 1 h 3 h 24 h 72 h
1 mol Ac 88 106 152 222
2 mol Ac 97 104 158 241
5 mol Ac 106 132 157 259
Table A 35 The results of Cu extraction carried out with citric acid for Sludge D
Extracted Cu Concentration (mg/kg DM)
at different extraction times
Citric Acid
Concentration
for kg DM 1 h 3 h 24 h 72 h
1 mol CA 8 11 3 4
2 mol CA 8 24 8 10
5 mol CA 26 42 18 5
Table A 36 The results of Cu extraction carried out with oxalic acid for Sludge D
Extracted Cu Concentration (mg/kg DM)
at different extraction times
Oxalic Acid
Concentration
for kg DM 1 h 3 h 24 h 72 h
1 mol OA 15 18 3 6
2 mol OA 26 22 23 1
5 mol OA - - - 24
115
Table A 37 The results of Cu extraction carried out with acetic acid for Sludge D
Extracted Cu Concentration (mg/kg DM)
at different extraction times
Acetic Acid
Concentration
for kg DM 1 h 3 h 24 h 72 h
1 mol Ac 31 100 98 25
2 mol Ac 49 128 122 38
5 mol Ac 59 97 39 69
Table A 38 The results of Pb extraction carried out with citric acid for Sludge D
Extracted Pb Concentration (mg/kg DM)
at different extraction times
Citric Acid
Concentration
for kg DM 1 h 3 h 24 h 72 h
1 mol CA - - - -
2 mol CA 24 105 - -
5 mol CA 178 49 90 114
Table A 39 The results of Pb extraction carried out with oxalic acid for Sludge D
Extracted Pb Concentration (mg/kg DM)
at different extraction times
Oxalic Acid
Concentration
for kg DM 1 h 3 h 24 h 72 h
1 mol OA 6 5 - 26
2 mol OA 54 39 - 16
5 mol OA 89 80 135 43
116
Table A 40 The results of Pb extraction carried out with acetic acid for Sludge D
Extracted Pb Concentration (mg/kg DM)
at different extraction times
Acetic Acid
Concentration
for kg DM 1 h 3 h 24 h 72 h
1 mol Ac 71 74 144 436
2 mol Ac 241 291 303 269
5 mol Ac 91 174 298 60
Table A 41 The results of Cd extraction carried out with citric acid for Sludge D
Extracted Cd Concentration (mg/kg DM)
at different extraction times
Citric Acid
Concentration
for kg DM 1 h 3 h 24 h 72 h
1 mol CA - - - 3
2 mol CA 0,21 - - -
5 mol CA 3,55 - - -
Table A 42 The results of Cd extraction carried out with oxalic acid for Sludge D
Extracted Cd Concentration (mg/kg DM)
at different extraction times
Oxalic Acid
Concentration
for kg DM 1 h 3 h 24 h 72 h
1 mol OA 0,68 - - -
2 mol OA 6,35 - 0,67 -
5 mol OA - - - 5,54
117
Table A 43 The results of Cd extraction carried out with acetic acid for Sludge D
Extracted Cd Concentration (mg/kg DM)
at different extraction times
Acetic Acid
Concentration
for kg DM 1 h 3 h 24 h 72 h
1 mol Ac - - 11 32
2 mol Ac - 1,48 - -
5 mol Ac - 0,56 - -
Table A 44 The results of Fe extraction carried out with citric acid for Sludge D
Extracted Fe Concentration (mg/kg DM)
at different extraction times
Citric Acid
Concentration
for kg DM 1 h 3 h 24 h 72 h
1 mol CA 69 144 338 339
2 mol CA 85 140 478 680
5 mol CA 93 213 555 837
Table A 45 The results of Fe extraction carried out with oxalic acid for Sludge D
Extracted Fe Concentration (mg/kg DM)
at different extraction times
Oxalic Acid
Concentration
for kg DM 1 h 3 h 24 h 72 h
1 mol OA 102 96 123 97
2 mol OA 196 254 267 285
5 mol OA 236 342 576 657